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<div class="pre-content"><div><div class="bk_prnt"><p class="small">NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.</p><p>Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. </p></div><div class="iconblock clearfix whole_rhythm no_top_margin bk_noprnt"><a class="img_link icnblk_img" title="All GeneReviews" href="/books/n/gene/"><img class="source-thumb" src="/corehtml/pmc/pmcgifs/bookshelf/thumbs/th-gene-lrg.png" alt="Cover of GeneReviews®" height="100px" width="80px" /></a><div class="icnblk_cntnt eight_col"><h2>GeneReviews<sup>®</sup> [Internet].</h2><a data-jig="ncbitoggler" href="#__NBK5191_dtls__">Show details</a><div style="display:none" class="ui-widget" id="__NBK5191_dtls__"><div>Adam MP, Feldman J, Mirzaa GM, et al., editors.</div><div>Seattle (WA): <a href="http://www.washington.edu" ref="pagearea=page-banner&targetsite=external&targetcat=link&targettype=publisher">University of Washington, Seattle</a>; 1993-2025.</div></div><div class="half_rhythm"><ul class="inline_list"><li style="margin-right:1em"><a class="bk_cntns" href="/books/n/gene/">GeneReviews by Title</a></li></ul></div><div class="bk_noprnt"><form method="get" action="/books/n/gene/" id="bk_srch"><div class="bk_search"><label for="bk_term" class="offscreen_noflow">Search term</label><input type="text" title="Search GeneReviews" id="bk_term" name="term" value="" data-jig="ncbiclearbutton" /> <input type="submit" class="jig-ncbibutton" value="Search GeneReviews" submit="false" style="padding: 0.1em 0.4em;" /></div></form><div><ul class="inline_list"><li><a href="/books/n/gene/advanced/">GeneReviews Advanced Search</a></li><li style="margin-left:.5em"><a href="/books/n/gene/helpadvsearch/">Help</a></li></ul></div></div></div><div class="icnblk_cntnt two_col"><div class="pagination bk_noprnt"><a class="active page_link prev" href="/books/n/gene/archived_chapters/" title="Previous page in this title">< Prev</a><a class="active page_link next" href="/books/n/gene/glossaryHelp/" title="Next page in this title">Next ></a></div></div></div></div></div>
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<div class="main-content lit-style" itemscope="itemscope" itemtype="http://schema.org/CreativeWork"><div class="meta-content fm-sec"><h1 id="_NBK5191_"><span class="title" itemprop="name"><i>GeneReviews</i> Glossary</span></h1></div><div class="body-content whole_rhythm" itemprop="text"><div id="terms_definitions"><h2 id="_terms_definitions_">Terms and Definitions</h2><p><a href="#IX-A">A</a> · <a href="#IX-B">B</a> · <a href="#IX-C">C</a> · <a href="#IX-D">D</a> · <a href="#IX-E">E</a> · <a href="#IX-F">F</a> · <a href="#IX-G">G</a> · <a href="#IX-H">H</a> · <a href="#IX-I">I</a> · <a href="#IX-K">K</a> · <a href="#IX-L">L</a> · <a href="#IX-M">M</a> · <a href="#IX-N">N</a> · <a href="#IX-O">O</a> · <a href="#IX-P">P</a> · <a href="#IX-Q">Q</a> · <a href="#IX-R">R</a> · <a href="#IX-S">S</a> · <a href="#IX-T">T</a> · <a href="#IX-U">U</a> · <a href="#IX-V">V</a> · <a href="#IX-W">W</a> · <a href="#IX-X">X</a></p><dl><h2 id="IX-A">A</h2><dt id="allele">allele</dt><dd><p>One version of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> at a given location (<a class="def" href="/books/NBK5191/def-item/locus/">locus</a>) along a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a>;
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<a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>; <a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a>;
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<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/locus/">locus</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>; <a class="def" href="/books/NBK5191/def-item/polymorphism/">polymorphism</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a>; <a class="def" href="/books/NBK5191/def-item/wild_type/">wild type</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-1/?report=objectonly" target="object" rid-ob="figobfurtherillus1">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
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</p></dd><dt id="allele-frequency">allele frequency</dt><dd><p>The proportion of individuals in a population who have inherited a specific variant</p></dd><dt id="allelic-heterogeneity">allelic heterogeneity</dt><dd><p>
|
|
Synonym: molecular heterogeneity
|
|
</p><p>Presence of different pathogenic variants in the same <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> and at the same <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> that cause a single disease <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a></p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/allele/">allele</a>
|
|
</p></dd><dt id="alternate-maternity">alternate maternity</dt><dd><p>
|
|
Synonym: non-maternity
|
|
</p><p>The situation in which the presumed mother of a particular individual is not the biological mother</p><p>Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/misattributed-parentage/">misattributed parentage</a></p></dd><dt id="alternate-paternity">alternate paternity</dt><dd><p>
|
|
Synonym: non-paternity
|
|
</p><p>The situation in which the presumed father of a particular individual is not the biological father</p><p>Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/misattributed-parentage/">misattributed parentage</a></p></dd><dt id="analyte">analyte</dt><dd><p>A chemical substance of interest; a biologic component whose properties (e.g., concentration, presence, absence) can be indicators of human disease;
|
|
in inherited conditions properties of analytes of interest are often measured in a biochemical/metabolic specialty laboratory to identify abnormalities
|
|
in a metabolic pathway.</p></dd><dt id="aneuploidy">aneuploidy</dt><dd><p>The occurrence of one or more extra or missing chromosomes leading to an unbalanced <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> complement, or any chromosome number that is not an exact multiple of the <a class="def" href="/books/NBK5191/def-item/haploid/">haploid</a> number</p></dd><dt id="anticipation">anticipation</dt><dd><p>The tendency in certain genetic disorders for individuals in successive generations to present at an earlier age and/or with more severe manifestations; often observed in
|
|
disorders resulting from the expression of a <a class="def" href="/books/NBK5191/def-item/nucleotide-repeat/">nucleotide repeat</a> expansion that tends to increase in size and have a more significant effect when passed from one generation to the next</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/intrafamilial-variability/">intrafamilial variability</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/nucleotide-repeat/">nucleotide repeat</a>; <a class="def" href="/books/NBK5191/def-item/trinucleotide-repeat/">trinucleotide repeat</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-10/?report=objectonly" target="object" rid-ob="figobfurtherillus10">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="ashkenazi-jewish">Ashkenazi Jewish</dt><dd><p>
|
|
Synonym: Eastern European Jewish
|
|
</p><p>The Eastern European Jewish population primarily from Germany,
|
|
Poland, and Russia, in contrast to the Sephardic Jewish population primarily from Spain, parts of France, Italy, and North Africa</p></dd><dt id="autosomal">autosomal</dt><dd><p>Referring to any of the chromosomes other than the sex-determining chromosomes (i.e., the X and Y) or to the genes on these chromosomes</p></dd><dt id="autosomal-dominant">autosomal dominant</dt><dd><p>Referring to a trait or disorder in which the <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> can be expressed in individuals who have one copy of a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> at a particular <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> (heterozygotes); specifically refers to a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> on one of the 22 pairs of autosomes (non-sex chromosomes)</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/de-novo/"><i>de novo</i></a>; <a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a>; <a class="def" href="/books/NBK5191/def-item/penetrance/">penetrance</a>; <a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p></dd><dt id="autosomal-recessive">autosomal recessive</dt><dd><p>Referring to a trait or disorder requiring the presence of <a class="def" href="/books/NBK5191/def-item/biallelic/">biallelic</a> pathogenic variants (i.e., <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a> or <a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a> variants) at a particular <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> in order to express an observable <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a>; specifically refers to genes on one of the 22 pairs of autosomes (non-sex chromosomes)</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>; <a class="def" href="/books/NBK5191/def-item/carrier-testing/">carrier testing</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a>; <a class="def" href="/books/NBK5191/def-item/consanguineous/">consanguineous</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a></p></dd><h2 id="IX-B">B</h2><dt id="background-risk">background risk</dt><dd><p>The proportion of individuals in a given population who are affected with a particular disorder or who have pathogenic variants in a certain <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>; often discussed in the <a class="def" href="/books/NBK5191/def-item/genetic-counseling/">genetic counseling</a> process as a comparison to the <a class="def" href="/books/NBK5191/def-item/proband/">proband</a>'s personal risk given his/her family history or other circumstances</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a>; <a class="def" href="/books/NBK5191/def-item/carrier-rate/">carrier rate</a></p></dd><dt id="base-pair">base pair</dt><dd><p>
|
|
Synonym: bp
|
|
</p><p>Two nitrogenous bases paired together in double-stranded DNA by weak bonds; specific pairing of these bases (adenine with thymine and guanine with cytosine) facilitates accurate
|
|
DNA replication; when quantified (e.g., 8 bp), refers to the physical length of a sequence of nucleotides</p></dd><dt id="benign-variant">benign variant</dt><dd><p>
|
|
Synonym: <a class="def" href="/books/NBK5191/def-item/polymorphism/">polymorphism</a>
|
|
</p><p>An alteration in DNA (distinct from the reference sequence) that is not associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or increased disease risk. A benign variant meets criteria to be
|
|
classified as benign according to the five-tier system of describing the clinical significance of genetic variants (See related terms).</p><p>Related terms:
|
|
<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="biallelic">biallelic</dt><dd><p>Referring to both alleles of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> pair. Biallelic variants may be <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a> or <a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a>.</p><p>Related terms:
|
|
<a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a>; <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/trans/"><i>trans</i></a></p></dd><h2 id="IX-C">C</h2><dt id="carrier">carrier</dt><dd><p>An individual with a recessive <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> at a particular <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> on one <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> of a pair who is not expected to develop manifestations of the related condition;
|
|
may also refer to an individual with a balanced chromosome rearrangement. Note regarding <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a> disorders: While the terms "<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>"
|
|
and "carrier" are often used synonymously in the literature, <i>GeneReviews</i> does not consider a heterozygote (who has - or is at risk of
|
|
developing - manifestations of a disorder) to be a carrier.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/carrier-rate/">carrier rate</a>; <a class="def" href="/books/NBK5191/def-item/carrier-testing/">carrier testing</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/obligate-heterozygote/">obligate heterozygote</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-19/?report=objectonly" target="object" rid-ob="figobfurtherillus19">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="carrier-rate">carrier rate</dt><dd><p>
|
|
Synonym: <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a> freqency
|
|
</p><p>The proportion of individuals in a population who have a single copy of a recessive variant that is pathogenic for a specific condition</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-20/?report=objectonly" target="object" rid-ob="figobfurtherillus20">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="carrier-testing">carrier testing</dt><dd><p>
|
|
Synonym: <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a> detection
|
|
</p><p>Testing used in the course of reproductive counseling to identify (typically) asymptomatic individuals who are <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> for a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> associated with a
|
|
specific <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a> or <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a> disorder</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-21/?report=objectonly" target="object" rid-ob="figobfurtherillus21">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="cdna">cDNA</dt><dd><p>Complementary DNA; the reverse-transcribed <a class="def" href="/books/NBK5191/def-item/mrna/">mRNA</a>. The cDNA sequence of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> differs from the <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a> sequence of the gene in that it does not include the introns;
|
|
cDNA does not occur in nature but can be synthesized from mRNA using a series of chemical reactions and may be analyzed to determine mRNA sequence. The nomenclature
|
|
system used to annotate sequence variants in the context of the coding sequence is based on complementary DNA. </p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/gdna/">gDNA</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/mrna/">mRNA</a></p></dd><dt id="chimerism">chimerism</dt><dd><p>Within a single individual or tissue, two or more genetically distinct cell lineages originating from different zygotes</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/mosaicism/">mosaicism</a>
|
|
</p></dd><dt id="chromosomal-microarray">chromosomal microarray</dt><dd><p>
|
|
Synonym: CMA
|
|
</p><p>Term that refers to methods used to detect copy number variants (losses or gains of <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> material), which may be benign, pathogenic, or of uncertain clinical significance.
|
|
A far more sensitive method than traditional karyotyping, CMA detects both large and small copy number variants. Depending on the method used, CMA may involve scanning of the whole
|
|
genome (also referred to as cytogenomic CMA), targeted regions of the genome, or a specific chromosome or chromosome segment. The CMA methods used most commonly in clinical practice include oligo (oligonucleotide) array,
|
|
SNP (single-nucleotide <a class="def" href="/books/NBK5191/def-item/polymorphism/">polymorphism</a>) array, and oligo/SNP combination array.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/comparative-genomic-hybridization/">comparative genomic hybridization</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/copy-number-variant/">copy number variant</a>; <a class="def" href="/books/NBK5191/def-item/snp-array/">SNP array</a>
|
|
</p></dd><dt id="chromosome">chromosome</dt><dd><p>Physical structure consisting of a large DNA molecule organized into genes and supported by proteins called chromatin</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/aneuploidy/">aneuploidy</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/autosomal/">autosomal</a>; <a class="def" href="/books/NBK5191/def-item/cytogenetic/">cytogenetic</a>; <a class="def" href="/books/NBK5191/def-item/karyotype/">karyotype</a></p></dd><dt id="chromosome-breakage-studies">chromosome breakage studies</dt><dd><p>Cytogenetic testing to detect an increased rate of <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> breakage or rearrangement in metaphase cells by exposing cell cultures to clastogenic agents such as diepoxybutane (DEB)
|
|
or mitomycin C (MMC); cell cultures not exposed to the DNA clastogenic agent are used as controls to measure the spontaneous rate of chromosome breakage or rearrangement.</p></dd><dt id="cis">
|
|
<i>cis</i>
|
|
</dt><dd><p>
|
|
Synonyms: <i>cis</i> configuration, coupling
|
|
</p><p>Referring to two variants on the same <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> (typically used to describe variants within the same <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>)</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/trans/">
|
|
<i>trans</i>
|
|
</a>
|
|
</p></dd><dt id="coding-region">coding region</dt><dd><p>
|
|
Synonyms: <a class="def" href="/books/NBK5191/def-item/open-reading-frame/">open reading frame</a>, ORF
|
|
</p><p>DNA sequence that has the potential to be transcribed into RNA and translated into protein; must include a start codon and termination codon</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/exon/">exon</a>; <a class="def" href="/books/NBK5191/def-item/intron/">intron</a>; <a class="def" href="/books/NBK5191/def-item/promoter-region/">promoter region</a>
|
|
</p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-26/?report=objectonly" target="object" rid-ob="figobfurtherillus26">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="codominant">codominant</dt><dd><p>Referring to two phenotypes being expressed at the same time from the same <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>; for example, the AB blood groups in humans</p></dd><dt id="comparative-genomic-hybridization">comparative genomic hybridization</dt><dd><p>Method in which two DNA samples (a control and a test sample), labeled in different fluorescent colors, are hybridized to a single
|
|
target to assay for relative losses (deletions) or gains (duplications) in the DNA of the test sample compared to the control</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/snp-array/">SNP array</a></p></dd><dt id="compound-heterozygous">compound heterozygous</dt><dd><p>Referring to two <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> variants present in <a class="def" href="/books/NBK5191/def-item/trans/"><i>trans</i></a> configuration within the same <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a> region of interest (typically within the same <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>)</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/biallelic/">biallelic</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/trans/"><i>trans</i></a></p></dd><dt id="congenital">congenital</dt><dd><p>Present at birth; not necessarily genetic</p></dd><dt id="consanguineous">consanguineous</dt><dd><p>Referring to reproductive partners who have a relatively close genetic relationship (e.g., cousins)</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/pedigree/">pedigree</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-30/?report=objectonly" target="object" rid-ob="figobfurtherillus30">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
|
</a>
|
|
</p></dd><dt id="consanguinity">consanguinity</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/consanguineous/">consanguineous</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/pedigree/">pedigree</a></p></dd><dt id="constitutional-variant">constitutional variant</dt><dd><p>A variant that is present in all somatic and <a class="def" href="/books/NBK5191/def-item/germline/">germline</a> cells and thus has the potential to be passed to subsequent generations; may be used synonymously
|
|
with "<a class="def" href="/books/NBK5191/def-item/germline-variant/">germline variant</a>" </p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/germline-variant/">germline variant</a>
|
|
</p></dd><dt id="contiguous-gene-deletion">contiguous gene deletion</dt><dd><p>Deletion of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> segment that encompasses two or more adjacent genes</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/deletion-syndrome/">deletion syndrome</a></p></dd><dt id="contiguous-gene-deletion-syndrome">contiguous gene deletion syndrome</dt><dd><p>A constellation of clinical findings caused by <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a> of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> segment that encompasses two or more adjacent genes</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion-syndrome/">deletion syndrome</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/fish/">FISH</a></p></dd><dt id="copy-number-variant">copy number variant</dt><dd><p>
|
|
Synonym: CNV
|
|
</p><p>Duplication or <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a> of a section of DNA. CNVs can be benign (normal), pathogenic, or of uncertain clinical significance. The method used to detect a CNV varies based on its
|
|
size (see <a class="def" href="/books/NBK5191/def-item/deletion-duplication-analysis/">deletion/duplication analysis</a>).</p><p>Related term: <a class="def" href="/books/NBK5191/def-item/single-nucleotide-variant/">single-nucleotide variant</a>
|
|
</p></dd><dt id="critical-region">critical region</dt><dd><p>The specific portion of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> or a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> that, when altered in some way (deleted, duplicated, or otherwise mutated), produces the
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characteristic set of phenotypic abnormalities associated with a particular syndrome or disorder</p></dd><dt id="custom-prenatal-testing">custom prenatal testing</dt><dd><p>Prenatal testing offered to families in which (a) <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>(s) have been identified in an affected family member in either a research or clinical laboratory; testing is not otherwise
|
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clinically available for <a class="def" href="/books/NBK5191/def-item/prenatal-diagnosis/">prenatal diagnosis</a>.</p></dd><dt id="custom-testing">custom testing</dt><dd><p>Testing offered to families in which (a) <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>(s) have been identified in an affected family member in either a research or clinical laboratory; testing is not otherwise clinically available.</p></dd><dt id="cytogenetic">cytogenetic</dt><dd><p>Referring to <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> abnormalities such as aneuploidies, deletions, duplications, and translocations</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>;
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<a class="def" href="/books/NBK5191/def-item/contiguous-gene-deletion/">contiguous gene deletion</a>; <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; <a class="def" href="/books/NBK5191/def-item/deletion-syndrome/">deletion syndrome</a>;
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<a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>; <a class="def" href="/books/NBK5191/def-item/fish/">FISH</a>; <a class="def" href="/books/NBK5191/def-item/karyotype/">karyotype</a></p></dd><h2 id="IX-D">D</h2><dt id="de-novo">
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<i>de novo</i>
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</dt><dd><p>Referring to a genetic variant that is present for the first time in one family member</p></dd><dt id="deletion">deletion</dt><dd><p>Absence of a segment of DNA; may be as small as a single base or as large as one or more genes. The method used to detect a deletion depends on the size of the deletion.</p><p>
|
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Related term:
|
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<a class="def" href="/books/NBK5191/def-item/deletion-duplication-analysis/">deletion/duplication analysis</a>
|
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</p></dd><dt id="deletion-duplication-analysis">deletion/duplication analysis</dt><dd><p>
|
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Synonym: copy number analysis
|
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</p><p>Testing that identifies deletions/duplications not routinely detectable by <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a> of the coding and flanking <a class="def" href="/books/NBK5191/def-item/intronic/">intronic</a> regions of <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a> DNA; included in the
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variety of methods that may be used are: <a class="def" href="/books/NBK5191/def-item/quantitative-pcr/">quantitative PCR</a>, multiplex ligation-dependent probe amplification (MLPA), and <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a> (CMA)
|
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that includes the <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>/<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> segment of interest.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a>;
|
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<a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>; <a class="def" href="/books/NBK5191/def-item/fish/">FISH</a>;
|
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<a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a>; <a class="def" href="/books/NBK5191/def-item/pcr/">PCR</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/sanger-sequencing/">Sanger sequencing</a>; <a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-314/?report=objectonly" target="object" rid-ob="figobfurtherillus314">
|
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
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</p></dd><dt id="deletion-syndrome">deletion syndrome</dt><dd><p>
|
|
Synonym: <a class="def" href="/books/NBK5191/def-item/microdeletion-syndrome/">microdeletion syndrome</a>
|
|
</p><p>A recognizable <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> caused by a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a> that spans one or more genes and may be too small to be detected using conventional
|
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<a class="def" href="/books/NBK5191/def-item/cytogenetic/">cytogenetic</a> methods; the deletion is typically detected by <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a> (CMA). Depending on the size of the deletion, other
|
|
techniques including <a class="def" href="/books/NBK5191/def-item/fish/">FISH</a> and <a class="def" href="/books/NBK5191/def-item/quantitative-pcr/">quantitative PCR</a> can sometimes be employed to identify the deletion.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray (CMA)</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>; <a class="def" href="/books/NBK5191/def-item/contiguous-gene-deletion-syndrome/">contiguous gene deletion syndrome</a>;
|
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<a class="def" href="/books/NBK5191/def-item/fish/">FISH</a>; <a class="def" href="/books/NBK5191/def-item/quantitative-pcr/">quantitative PCR</a></p></dd><dt id="digenic">digenic</dt><dd><p>Referring to expression of a <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> that requires the presence of pathogenic variants in two different genes</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/oligogenic/">oligogenic</a>; <a class="def" href="/books/NBK5191/def-item/trigenic/">trigenic</a></p></dd><dt id="domain">domain</dt><dd><p>A specific region or amino acid sequence in a protein associated with a particular function or corresponding segment of DNA</p></dd><dt id="dominant-negative">dominant-negative</dt><dd><p>Referring to a single, <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> which produces a protein that interferes with (i.e., dimerizes or combines with, or blocks) the normal protein
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produced by the other <a class="def" href="/books/NBK5191/def-item/allele/">allele</a>, adversely affecting protein function. In cases of polymeric molecules, such as collagen, dominant-negative variants
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are often more deleterious than variants resulting in no <a class="def" href="/books/NBK5191/def-item/gene-product/">gene product</a> (<a class="def" href="/books/NBK5191/def-item/null/">null</a> variants).</p></dd><dt id="double-heterozygosity">double heterozygosity</dt><dd><p>The presence in an individual of a <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> variant in two different <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a> regions of interest (typically, a heterozygous variant
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in each of two different genes). The clinical consequences of double heterozygosity depend on the related disorder(s) and the mode(s)
|
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of inheritance of the disorder(s).</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>
|
|
</p></dd><dt id="duplication">duplication</dt><dd><p>The presence of one or more additional copies of a segment of DNA; may be as small as a single base or as large as one or more genes. The method used to detect
|
|
a duplication depends on the size of the duplication.</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/deletion-duplication-analysis/">deletion/duplication analysis</a>
|
|
</p></dd><dt id="dysmorphic">dysmorphic</dt><dd><p>Referring to visible morphologic findings that differ from those commonly seen in the general population or that are expected from the family background</p></dd><h2 id="IX-E">E</h2><dt id="epigenetic">epigenetic</dt><dd><p>Referring to chemical alterations to DNA nucleotides or proteins that control <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> expression but do not alter the DNA sequence</p></dd><dt id="epimutation">epimutation</dt><dd><p>A heritable change in <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> activity that is not associated with a DNA variant but rather with gain or loss of DNA <a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a> or other heritable modifications of chromatin </p><p>(Reprinted from <i>Trends in Genetics</i>, 30:519-20. Oey H, Whitelaw E. On the meaning of the word "epimutation." Copyright 2014, with permission from Elsevier.)</p></dd><dt id="exome">exome</dt><dd><p> The part of the genome that includes all coding nuclear DNA sequences. The human exome comprises approximately
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180,000 exons that are transcribed into mature RNA.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>;
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<a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>; <a class="def" href="/books/NBK5191/def-item/exon/">exon</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a>;
|
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<a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a></p></dd><dt id="exome-array">exome array</dt><dd><p>A microarray designed to determine <a class="def" href="/books/NBK5191/def-item/exon/">exon</a>-level copy number for as many genes associated with disease as possible regardless of <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or
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clinical features associated with the genes</p><p>
|
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Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/gene-targeted-array/">gene-targeted array</a>
|
|
</p></dd><dt id="exome-sequencing">exome sequencing</dt><dd><p>Sequence analysis of the exons of protein-coding genes in the genome typically performed by target
|
|
enrichment or capture of exons followed by <a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a> (NGS). Exome sequencing techniques have nonstandardized,
|
|
highly variable coverage; of particular note are regions of the <a class="def" href="/books/NBK5191/def-item/exome/">exome</a> refractory to accurate sequencing by this method
|
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(including genes with a <a class="def" href="/books/NBK5191/def-item/pseudogene/">pseudogene</a>, highly repetitive coding regions, and large deletions and duplications). Laboratories may also
|
|
include <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a> of some noncoding regions of the genome (e.g., promoters, highly conserved regulatory sequences). Note
|
|
that the term "exome sequencing" is preferred over the formerly used term "<a class="def" href="/books/NBK5191/def-item/whole-exome-sequencing/">whole-exome sequencing</a>" because coverage of the exome
|
|
is less than 100%, and thus the "whole" exome is not sequenced.</p><p>Related terms:
|
|
<a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>; <a class="def" href="/books/NBK5191/def-item/exome/">exome</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/exon/">exon</a>; <a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a></p></dd><dt id="exon">exon</dt><dd><p>Coding sequence of DNA present in mature messenger RNA</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>; <a class="def" href="/books/NBK5191/def-item/intron/">intron</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-52/?report=objectonly" target="object" rid-ob="figobfurtherillus52">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
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</p></dd><h2 id="IX-F">F</h2><dt id="familial">familial</dt><dd><p>Referring to a condition or variant that occurs in more than one family member</p></dd><dt id="first-degree-relative">first-degree relative</dt><dd><p>A parent, full sib, or child of an individual</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/pedigree/">pedigree</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/second-degree-relative/">second-degree relative</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-59/?report=objectonly" target="object" rid-ob="figobfurtherillus59">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
|
</p></dd><dt id="fish">FISH</dt><dd><p>Fluorescent in situ hybridization; a technique used to identify the presence of specific chromosomes or chromosomal regions through hybridization (attachment) of fluorescently
|
|
labeled DNA probes to denatured chromosomal DNA. Examination under fluorescent lighting detects the presence of the hybridized fluorescent signal (and hence presence of the
|
|
<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> material) or absence of the hybridized fluorescent signal (and hence absence of the chromosome material).</p><p> With <b>interphase FISH</b>, probes are introduced directly to the interphase cell. Interphase FISH is often used for rapid detection of specific types of <a class="def" href="/books/NBK5191/def-item/aneuploidy/">aneuploidy</a> in
|
|
fetal cells and for the detection of certain deletions, duplications, and other abnormalities in tumor cells. In contrast to metaphase FISH, interphase FISH does not permit
|
|
visualization of the actual chromosomes; therefore, certain structural rearrangements or aneuploidy will not be detected.</p><p>With <b>metaphase FISH</b>, cells progress through the division process until metaphase, when chromosomes are condensed and can be individually distinguished. In contrast
|
|
to interphase FISH, metaphase FISH permits visualization of the actual chromosomes as well as the general location of the abnormality on the <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>.</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/aneuploidy/">aneuploidy</a>
|
|
</p></dd><dt id="fluorescent-in-situ-hybridization">fluorescent in situ hybridization</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/fish/">FISH</a>.</p></dd><dt id="founder-effect">founder effect</dt><dd><p>The higher-than-average frequency of a rare <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> in a population <a class="def" href="/books/NBK5191/def-item/isolated/">isolated</a> over time by geography, language, and/or culture, resulting from the presence of the allele in an
|
|
early member or members ("founders") of that group. For example, a founder effect accounts for the high incidence of Huntington disease in the Lake Maracaibo region of Venezuela.</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/founder-variant/">founder variant</a>
|
|
</p></dd><dt id="founder-variant">founder variant</dt><dd><p> A <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> observed in high frequency in a specific population due to the presence of the variant in a single ancestor or small number of ancestors</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a>; <a class="def" href="/books/NBK5191/def-item/founder-effect/">founder effect</a></p></dd><dt id="frameshift-variant">frameshift variant</dt><dd><p>
|
|
Synonyms: out-of-frame variant, out-of-frame <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>
|
|
</p><p>A <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>, <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>, or <a class="def" href="/books/NBK5191/def-item/insertion/">insertion</a> within an <a class="def" href="/books/NBK5191/def-item/exon/">exon</a> involving a number of base pairs that is not a multiple of three, consequently disrupting the triplet reading frame
|
|
and usually leading to the creation of a premature termination (stop) codon and subsequent loss of normal protein product</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>
|
|
</p></dd><dt id="full-penetrance-allele">full-penetrance allele</dt><dd><p>In <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a>, <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>, and <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a> disorders caused by <a class="def" href="/books/NBK5191/def-item/nucleotide-repeat/">nucleotide repeat</a> expansion, an abnormally large <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> that is associated with disease manifestations</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/anticipation/">anticipation</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/reduced-penetrance-allele/">reduced-penetrance allele</a>; <a class="def" href="/books/NBK5191/def-item/trinucleotide-repeat/">trinucleotide repeat</a></p></dd><h2 id="IX-G">G</h2><dt id="gain-of-function">gain-of-function</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> variant associated with one of the following abnormalities: an increase in one or more functions of the <a class="def" href="/books/NBK5191/def-item/gene-product/">gene product</a>;
|
|
a novel function of the gene product; a change in timing of gene expression</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/loss-of-function/">loss-of-function</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a></p></dd><dt id="gdna">gDNA</dt><dd><p>Genomic DNA. The DNA in a cell that is chromosomal DNA. Genomic DNA does not include mitochondrial DNA.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/cdna/">cDNA</a>;
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|
<a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a>; <a class="def" href="/books/NBK5191/def-item/mrna/">mRNA</a></p></dd><dt id="gene">gene</dt><dd><p>The basic unit of heredity, consisting of a segment of DNA arranged in a linear manner along a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>. A gene codes for a specific protein, a segment of protein, or <a class="def" href="/books/NBK5191/def-item/noncoding-rna/">noncoding RNA</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele/">allele</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a>; <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-66/?report=objectonly" target="object" rid-ob="figobfurtherillus66">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
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</p></dd><dt id="gene-conversion">gene conversion</dt><dd><p>The transfer of DNA sequences between two very similar genes, most often by <a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a> during meiosis; can be a mechanism for mutation if the
|
|
transfer of material disrupts the coding sequence of the <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or if the transferred material itself contains one or more pathogenic variants</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/pseudogene/">pseudogene</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/recombination/">recombination</a>; <a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a></p></dd><dt id="gene-product">gene product</dt><dd><p>Most genes are transcribed into segments of RNA (ribonucleic acid), which are translated into proteins. Both RNA and proteins are products expressed by the <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>; <a class="def" href="/books/NBK5191/def-item/isoforms/">isoforms</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-68/?report=objectonly" target="object" rid-ob="figobfurtherillus68">
|
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
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</p></dd><dt id="gene-targeted-array">gene-targeted array</dt><dd><p>A microarray designed to determine <a class="def" href="/books/NBK5191/def-item/exon/">exon</a>-level copy number for a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or set of genes associated with a <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or specific clinical feature</p><p>
|
|
Related term:
|
|
<a class="def" href="/books/NBK5191/def-item/exome-array/">exome array</a>
|
|
</p></dd><dt id="gene-therapy">gene therapy</dt><dd><p>Treatment of a genetic disorder by replacing or manipulating an abnormal <a class="def" href="/books/NBK5191/def-item/gene/">gene</a></p></dd><dt id="genetic-counseling">genetic counseling</dt><dd><p>The process of providing individuals and families with information on the nature, inheritance, and implications of genetic disorders to help them make informed
|
|
medical and personal decisions. Genetic counseling deals with risk assessment and the use of family history and testing to clarify genetic status for family members.</p></dd><dt id="genome-sequencing">genome sequencing</dt><dd><p>Sequence analysis of the genome including coding and noncoding regions typically performed
|
|
by <a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a> (NGS) of sheared <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a> DNA; genome sequencing techniques have nonstandardized, highly variable
|
|
coverage. Note that "genome sequencing" is preferred over the formerly used term "<a class="def" href="/books/NBK5191/def-item/whole-genome-sequencing/">whole-genome sequencing</a>" because coverage of
|
|
the genome is less than 100%, and thus the "whole" genome is not sequenced.</p><p>Related terms:
|
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<a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>; <a class="def" href="/books/NBK5191/def-item/genomic/">genomic</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a></p></dd><dt id="genomic">genomic</dt><dd><p>Referring to the human genome, which comprises the DNA in all chromosomes and in mitochondria</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/gdna/">gDNA</a>; <a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a></p></dd><dt id="genotype">genotype</dt><dd><p>Commonly, the <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> or set of alleles at a single <a class="def" href="/books/NBK5191/def-item/locus/">locus</a>; less commonly, the set of alleles at multiple or all loci</p></dd><dt id="genotype-phenotype-correlations">genotype-phenotype correlations</dt><dd><p>Associations between an individual's <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a> and the resulting pattern of clinical findings, or <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a>; <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a></p></dd><dt id="genotyping">genotyping</dt><dd><p>Molecular assay designed to detect the presence or absence of a specific variant (or variants) in DNA; variants in DNA not targeted by the assay will not be detected.</p></dd><dt id="germline">germline</dt><dd><p>The cell line from which egg or sperm cells (gametes) are derived</p></dd><dt id="germline-mosaicism">germline mosaicism</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a>.</p></dd><dt id="germline-variant">germline variant</dt><dd><p>A variant that is presumed to be present in all germ (egg and sperm) cells and somatic cells. Unlike a somatic variant (i.e., a
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variant that arises spontaneously in a somatic cell), a germline variant can be transmitted to offspring.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/constitutional-variant/">constitutional variant</a>;
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<a class="def" href="/books/NBK5191/def-item/de-novo/"><i>de novo</i></a>; <a class="def" href="/books/NBK5191/def-item/germline/">germline</a>; <a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a></p></dd><dt id="gonadal-mosaicism">gonadal mosaicism</dt><dd><p>
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Synonym: <a class="def" href="/books/NBK5191/def-item/germline-mosaicism/">germline mosaicism</a>
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</p><p>Mosaicism confined to or involving gonadal cells</p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/somatic-mosaicism/">somatic mosaicism</a>
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</p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-33/?report=objectonly" target="object" rid-ob="figobfurtherillus33">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><h2 id="IX-H">H</h2><dt id="haploid">haploid</dt><dd><p>Half the diploid or normal number of chromosomes in a somatic cell; the number of chromosomes in a gamete (egg or sperm) cell, which in humans is 23 chromosomes,
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one <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> from each chromosome pair</p></dd><dt id="haploinsufficiency">haploinsufficiency</dt><dd><p>A cause of disease in which the protein product from a single normal <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> is insufficient -- given the presence of a <a class="def" href="/books/NBK5191/def-item/loss-of-function/">loss-of-function</a>
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<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> on the other allele -- to prevent the appearance of an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a></p></dd><dt id="hemizygous">hemizygous</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> normally present in only a single copy; usually an <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a> gene in a male</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>;
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<a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a>; <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p></dd><dt id="heteroplasmic">heteroplasmic</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/heteroplasmy/">heteroplasmy</a>.</p></dd><dt id="heteroplasmy">heteroplasmy</dt><dd><p>The presence within a single cell of both normal and mutated mitochondrial DNA (mtDNA); the proportion of normal to mutated mtDNA (i.e., the mutant load) may vary in
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different tissues and is a critical factor in the expression and severity of disease caused by mutation of mtDNA.</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/mitochondrial-inheritance/">mitochondrial inheritance</a>; <a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p></dd><dt id="heterozygote">heterozygote</dt><dd><p>An individual with two different alleles at a particular <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> (one on each <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> of a pair), one of which is usually pathogenic. The risk that an individual who is <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a>
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for a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> will have manifestations of the related <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> depends on the specific disorder and the <a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a> of the disorder.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>;
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<a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a>; <a class="def" href="/books/NBK5191/def-item/obligate-heterozygote/">obligate heterozygote</a></p></dd><dt id="heterozygous">heterozygous</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>. </p></dd><dt id="histone">histone</dt><dd><p>A member of the family of proteins (referred to as histones) around which nuclear DNA is wrapped to facilitate condensation into chromosomes
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and access for transcription. Eight histone proteins form a single histone core.</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>;
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<a class="def" href="/books/NBK5191/def-item/epigenetic/">epigenetic</a>; <a class="def" href="/books/NBK5191/def-item/nucleosome/">nucleosome</a></p></dd><dt id="homoplasmic">homoplasmic</dt><dd><p>Characterized by <a class="def" href="/books/NBK5191/def-item/homoplasmy/">homoplasmy</a></p></dd><dt id="homoplasmy">homoplasmy</dt><dd><p>The presence of identical alleles at all mitochodondrial loci within a single cell or organism</p></dd><dt id="homozygous">homozygous</dt><dd><p>Denoting a variant (distinct from the reference sequence) that is present on both alleles of a given <a class="def" href="/books/NBK5191/def-item/gene/">gene</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/compound-heterozygous/">compound heterozygous</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a></p></dd><dt id="hot-spot">hot spot</dt><dd><p>A DNA sequence that is highly susceptible to mutation because of some inherent instability, a tendency toward <a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a>, or chemical predisposition to single-nucleotide
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substitutions; a region where pathogenic variants are observed with greater frequency</p></dd><dt id="hypomorphic">hypomorphic</dt><dd><p>Referring to a variant characterized by partial loss of <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> activity (including reduction in protein production or function)</p></dd><h2 id="IX-I">I</h2><dt id="idiopathic">idiopathic</dt><dd><p>Relating to or denoting a disease or condition for which the cause is unknown</p></dd><dt id="imprinted">imprinted</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>.</p></dd><dt id="imprinting">imprinting</dt><dd><p>The process by which maternally and paternally derived chromosomes are uniquely chemically modified (usually by <a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a>), leading to different expression of a certain
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<a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or genes on those chromosomes depending on their parental origin. Patterns of gene expression and repression vary between <a class="def" href="/books/NBK5191/def-item/imprinted/">imprinted</a> regions.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a>;
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<a class="def" href="/books/NBK5191/def-item/trisomy-rescue/">trisomy rescue</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a></p></dd><dt id="inactivating">inactivating</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/loss-of-function/">loss-of-function</a>.</p></dd><dt id="indel">indel</dt><dd><p>Abbreviation for an <a class="def" href="/books/NBK5191/def-item/insertion/">insertion</a> (i.e., <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>) or a <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a> of nucleotides, typically within a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>;
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<a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>; <a class="def" href="/books/NBK5191/def-item/insertion/">insertion</a></p></dd><dt id="in-frame">in-frame</dt><dd><p>Referring to a variant (usually a small <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a> or <a class="def" href="/books/NBK5191/def-item/insertion/">insertion</a>) that does not cause a shift in the triplet reading frame. Such variants can be pathogenic
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when they lead to the synthesis of an abnormal protein product (i.e., one with one or more missing or inserted amino acids).</p></dd><dt id="insertion">insertion</dt><dd><p>Presence of extra DNA in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or other DNA region; may be as small as a single base or as large as one or more genes;
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if the insertion occurs in a <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>, it may potentially disrupt gene function. An insertion is considered a <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a> when the inserted DNA
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is a perfect match to the adjacent DNA. </p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/deletion/">duplication</a>
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</p></dd><dt id="interfamilial-variability">interfamilial variability</dt><dd><p>Variability in clinical presentation of a particular disorder among affected individuals from different families</p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/intrafamilial-variability/">intrafamilial variability</a>
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</p></dd><dt id="intrafamilial-variability">intrafamilial variability</dt><dd><p>Variability in clinical presentation of a particular disorder among affected individuals within the same immediate or extended family</p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/interfamilial-variability/">interfamilial variability</a>
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</p></dd><dt id="intron">intron</dt><dd><p>Noncoding sequence of DNA removed from mature messenger RNA prior to translation</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>;
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<a class="def" href="/books/NBK5191/def-item/exon/">exon</a>; <a class="def" href="/books/NBK5191/def-item/intronic/">intronic</a>; <a class="def" href="/books/NBK5191/def-item/splicing/">splicing</a></p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-107/?report=objectonly" target="object" rid-ob="figobfurtherillus107">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="intronic">intronic</dt><dd><p>Referring to DNA or variants in DNA within an <a class="def" href="/books/NBK5191/def-item/intron/">intron</a></p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/intron/">intron</a>
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</p></dd><dt id="isoelectric-focusing">isoelectric focusing</dt><dd><p>Method by which proteins migrate in a matrix according to the pH; an amino acid substitution can change the isoelectric point of a protein.</p></dd><dt id="isoforms">isoforms</dt><dd><p>Similar forms of a protein produced by different versions of messenger RNA resulting from use of different promoters, skipping of exons, or differences in <a class="def" href="/books/NBK5191/def-item/splicing/">splicing</a>; may be tissue specific.</p></dd><dt id="isolated">isolated</dt><dd><p>Referring to a finding that occurs in the absence of other systemic involvement</p></dd><h2 id="IX-K">K</h2><dt id="karyotype">karyotype</dt><dd><p>A photographic representation of the chromosomes of a single cell, cut and arranged in pairs based on their size and banding pattern according to a standard classification</p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-111/?report=objectonly" target="object" rid-ob="figobfurtherillus111">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><h2 id="IX-L">L</h2><dt id="likely-benign">likely benign</dt><dd><p>Referring to an alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (distinct from the reference sequence) that is very unlikely to be associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or increased disease risk. A likely benign variant
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meets most, but not all, criteria to be classified as benign according to the five-tier system for describing the clinical significance of genetic variants (see Related terms). </p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
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<a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>;
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<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="likely-pathogenic">likely pathogenic</dt><dd><p>Referring to an alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (distinct from the reference sequence) that is likely to be associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or increased disease risk. A likely pathogenic
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variant meets most but not all criteria to be classified as pathogenic according to the five-tier system for describing the clinical significance of genetic events. A likely pathogenic
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variant is considered diagnostic and can be used for clinical decision making (see Related terms).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
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<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>;
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<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="locus">locus</dt><dd><p>The physical site or location of a specific <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> on a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>. OMIM (http://omim.org) is the standard reference used for locus information included in <i>GeneReviews</i>.</p></dd><dt id="locus-name">locus name</dt><dd><p>An informally assigned abbreviation used in the process of mapping to designate a putative <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> prior to gene identification; once the gene is identified, the locus name is generally replaced by a formally assigned gene symbol (which often differs from the locus name).</p></dd><dt id="loss-of-function">loss-of-function</dt><dd><p>Referring to a variant associated with partial or total loss of the function of a <a class="def" href="/books/NBK5191/def-item/gene-product/">gene product</a> </p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/gain-of-function/">gain-of-function</a>; <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a></p></dd><dt id="loss-of-heterozygosity">loss of heterozygosity</dt><dd><p>
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Synonym: LOH
|
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</p><p>Loss of one of the two alleles at a <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> or at multiple loci leading to a <a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a> or <a class="def" href="/books/NBK5191/def-item/hemizygous/">hemizygous</a> state. LOH can be caused by a variety of
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genetic mechanisms including <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>, <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> loss, and mitotic crossing over.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; <a class="def" href="/books/NBK5191/def-item/hemizygous/">hemizygous</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>;
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<a class="def" href="/books/NBK5191/def-item/homozygous/">homozygous</a></p></dd><h2 id="IX-M">M</h2><dt id="manifesting-heterozygote">manifesting heterozygote</dt><dd><p>An individual who has at a particular <a class="def" href="/books/NBK5191/def-item/locus/">locus</a> a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> on one <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> and a <a class="def" href="/books/NBK5191/def-item/wild_type/">wild type</a>
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<a class="def" href="/books/NBK5191/def-item/allele/">allele</a> on the other chromosome, and who has findings of the disorder; generally refers to a clinically affected
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female with a <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> pathogenic variant in an <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a> <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>. The <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> is usually less severe than in
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a <a class="def" href="/books/NBK5191/def-item/hemizygous/">hemizygous</a> male with the same pathogenic variant.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a>; <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p></dd><dt id="methylation">methylation</dt><dd><p>The attachment of methyl groups to DNA at cytosine bases; correlated with reduced transcription of the <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> and thought to be the principal mechanism
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in <a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a> and <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>;
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<a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a></p></dd><dt id="methylation-analysis">methylation analysis</dt><dd><p>Testing that evaluates the <a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a> status of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (attachment of methyl groups to DNA cytosine bases). Genes that are methylated are not expressed.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>;
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<a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a>; <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>;
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<a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a></p></dd><dt id="microdeletion-syndrome">microdeletion syndrome</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/deletion-syndrome/">deletion syndrome</a>.</p></dd><dt id="microsatellite">microsatellite</dt><dd><p>
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Synonyms: satellite DNA, short tandem repeats
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|
</p><p>A segment of DNA two to five nucleotides in length (di-, tri-, tetra-, or pentanucleotide repeats) typically repeated five to 50 times or more. Microsatellite
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DNA is dispersed throughout the genome in noncoding regions between genes or within genes (i.e., in introns). Microsatellite DNA is inherently unstable and
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susceptible to mutation.</p></dd><dt id="misattributed-parentage">misattributed parentage</dt><dd><p>Refers to the situation in which a person reported to be the biological father or mother of a child is in fact not the biological parent. Factors that may
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result in misattributed parentage include assisted reproduction (i.e., use of a donor sperm, donor egg, or donor embryo), undisclosed adoption, and <a class="def" href="/books/NBK5191/def-item/alternate-paternity/">alternate paternity</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/alternate-maternity/">alternate maternity</a>;
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<a class="def" href="/books/NBK5191/def-item/alternate-paternity/">alternate paternity</a></p></dd><dt id="mismatch-repair">mismatch repair</dt><dd><p>The DNA "proofreading" system that identifies, excises, and corrects errors in the pairing of the bases during DNA replication. Mutation of the genes encoding
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|
mismatch repair proteins can result in susceptibility to some cancers.</p></dd><dt id="missense">missense</dt><dd><p>Referring to a single base-pair substitution that results in the translation of a different amino acid at that position; can be pathogenic or benign</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
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<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>;
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<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>; <a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="mitochondrial-inheritance">mitochondrial inheritance</dt><dd><p>
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Synonym: maternal inheritance
|
|
</p><p>Mitochondria - cytoplasmic organelles that produce the energy source ATP for most chemical reactions in the body - contain their own distinct genome; pathogenic variants in
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mitochondrial genes are responsible for several recognized syndromes and are always maternally inherited because mitochondria are transmitted by the ova, not the sperm.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/heteroplasmy/">heteroplasmy</a>;
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<a class="def" href="/books/NBK5191/def-item/homoplasmy/">homoplasmy</a>; <a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a>; <a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-131/?report=objectonly" target="object" rid-ob="figobfurtherillus131">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="mode-of-inheritance">mode of inheritance</dt><dd><p>
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Synonyms: inheritance pattern, pattern of inheritance
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</p><p>The manner in which a particular genetic condition is passed from one generation to the next. Autosomal dominant, <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>, <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a>, <a class="def" href="/books/NBK5191/def-item/multifactorial/">multifactorial</a>, and
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<a class="def" href="/books/NBK5191/def-item/mitochondrial-inheritance/">mitochondrial inheritance</a> are examples.</p></dd><dt id="molecular-combing">molecular combing</dt><dd><p>Technique in which <a class="def" href="/books/NBK5191/def-item/fluorescent-in-situ-hybridization/">fluorescent in situ hybridization</a> (<a class="def" href="/books/NBK5191/def-item/fish/">FISH</a>) probes of known sequence are hybridized to uniformly stretched long fragments of DNA to determine content of and distance between targeted sequence with
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high resolution. Used to assess repetitive regions of DNA not amenable to <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>.</p></dd><dt id="molecular-genetic-testing">molecular genetic testing</dt><dd><p>A term widely used in clinical genetics encompassing the diverse techniques used to identify the molecular basis of genetic
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disease. Examples of molecular genetic tests include: <a class="def" href="/books/NBK5191/def-item/genotyping/">genotyping</a> to detect specific pathogenic variants;
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sequencing of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> to detect pathogenic variants; amplification or hybridization methods (e.g., qPCR, array CGH, MLPA) to
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detect copy number variants involving one or more genes; <a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a>-specific techniques to detect <a class="def" href="/books/NBK5191/def-item/epigenetic/">epigenetic</a> changes that
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influence gene expression; and <a class="def" href="/books/NBK5191/def-item/exome/">exome</a> and <a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a>.</p></dd><dt id="monoallelic">monoallelic</dt><dd><p>Referring to one <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> pair, as opposed to <a class="def" href="/books/NBK5191/def-item/biallelic/">biallelic</a>, which refers to both alleles of a gene pair.</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a>; <a class="def" href="/books/NBK5191/def-item/cis/"><i>cis</i></a></p></dd><dt id="monosomy">monosomy</dt><dd><p>The presence of only one <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> from a pair; partial monosomy refers to the presence of only one copy of a segment of a chromosome</p></dd><dt id="mosaicism">mosaicism</dt><dd><p>Within a single individual or tissue, the <a class="def" href="/books/NBK5191/def-item/postzygotic/">postzygotic</a> occurrence of two or more cell lines with a different genetic or chromosomal composition that are derived from a single fertilized egg. Mosaicism may involve somatic cells,
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gonadal cells, and/or tumor cells.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a>; <a class="def" href="/books/NBK5191/def-item/germline-variant/">germline variant</a>;
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<a class="def" href="/books/NBK5191/def-item/postzygotic/">postzygotic</a>; <a class="def" href="/books/NBK5191/def-item/somatic-mosaicism/">somatic mosaicism</a></p></dd><dt id="mrna">mRNA</dt><dd><p>Messenger RNA</p></dd><dt id="multifactorial">multifactorial</dt><dd><p>Referring to the combined contribution of one or more often unspecified genes and environmental factors, often unknown, in the causation of a particular finding</p></dd><dt id="multigene-panel">multigene panel</dt><dd><p>Simultaneous molecular testing of multiple genes associated with the same or similar clinical phenotypes. The genes included in the panel and the diagnostic <a class="def" href="/books/NBK5191/def-item/sensitivity/">sensitivity</a>
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of the testing used for each <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> vary by laboratory and over time. Methods used may include <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>, <a class="def" href="/books/NBK5191/def-item/deletion-duplication-analysis/">deletion/duplication analysis</a>, or other non-sequencing-based tests.</p></dd><h2 id="IX-N">N</h2><dt id="next-generation-sequencing">next-generation sequencing (NGS)</dt><dd><p>
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Synonyms: massively parallel sequencing (MPS), high-throughput sequencing
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</p><p>Referring to several different technologies, all of which allow simultaneous <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a> of millions of DNA fragments. NGS can detect variations as small as a single-base
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substitution; depending on the methods used, NGS may detect copy number variants (CNVs). NGS is used primarily for multigene panels and genome, <a class="def" href="/books/NBK5191/def-item/exome/">exome</a>, and transcriptome
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sequencing. NGS may also be used for single-<a class="def" href="/books/NBK5191/def-item/gene/">gene</a> testing (e.g., targeting of a single gene on a mult-gene panel or sequencing of a large multiexon gene). Results from
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NGS may require confirmation by an alternative sequencing method.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/copy-number-variant/">copy number variant</a>;
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<a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>; <a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a>;
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<a class="def" href="/books/NBK5191/def-item/multigene-panel/">multigene panel</a>; <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>;
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<a class="def" href="/books/NBK5191/def-item/single-nucleotide-variant/">single-nucleotide variant</a></p></dd><dt id="nonallelic-homologous-recombination">nonallelic homologous recombination</dt><dd><p>
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Synonym: NAHR
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</p><p>The result of a process in which segmental duplications (low copy repeats) flanking a region misalign during meiosis, followed by <a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a> between
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the segmental duplications. The process can produce gametes with the <a class="def" href="/books/NBK5191/def-item/recurrent-deletion/">recurrent deletion</a> or the reciprocal recurrent <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>. </p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a>
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</p><p>
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<a class="img_link" href="/books/NBK5191/box/disease_example-216/?report=objectonly" target="object" rid-ob="figobdiseaseexample216">
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<span class="graphic"><img src="/books/NBK5191/bin/DiseaseExample.jpg" alt="Image DiseaseExample.jpg" /></span>
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</a>
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<a class="img_link" href="/books/NBK5191/box/further_illus-216/?report=objectonly" target="object" rid-ob="figobfurtherillus216">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="noncoding-rna">noncoding RNA</dt><dd><p>Functional RNA (transcribed from a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>) that is not translated into protein</p></dd><dt id="nonsense-variant">nonsense</dt><dd><p>Referring to a variant in which a codon is changed from one that specifies an amino acid to one that specifies a termination (stop)</p></dd><dt id="normal-variant">normal variant</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>.</p></dd><dt id="nucleosome">nucleosome</dt><dd><p>The functional unit of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>, consisting of the length of DNA and the core of <a class="def" href="/books/NBK5191/def-item/histone/">histone</a> proteins around which DNA is wrapped.
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The nucleosome is the building block of the chromosome.</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>; <a class="def" href="/books/NBK5191/def-item/histone/">histone</a></p></dd><dt id="nucleotide-repeat">nucleotide repeat</dt><dd><p>Sequence of n nucleotides repeated a number of times in tandem; can occur within or near a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>. The size of nucleotide repeats varies: smaller numbers of repeats are
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common and not associated with phenotypic abnormalities; abnormally large numbers of repeats may be associated with phenotypic abnormalities and are classified as (in
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increasing order): mutable normal alleles, premutations, reduced-<a class="def" href="/books/NBK5191/def-item/penetrance/">penetrance</a> alleles, and full-penetrance alleles.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/premutation/">premutation</a>;
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<a class="def" href="/books/NBK5191/def-item/trinucleotide-repeat/">trinucleotide repeat</a></p></dd><dt id="null">null</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> that results in either no <a class="def" href="/books/NBK5191/def-item/mrna/">mRNA</a>, no protein, or a nonfunctional protein</p></dd><h2 id="IX-O">O</h2><dt id="obligate-heterozygote">obligate heterozygote</dt><dd><p>An individual who must be <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> for a variant based on analysis of the family history; applies to disorders inherited in an <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a> or <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a> manner. The term "obligate heterozygote" can also refer to individuals with an <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a> disorder whose position in a
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<a class="def" href="/books/NBK5191/def-item/pedigree/">pedigree</a> indicates that they must be heterozygous even though they do not manifest the <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a>;
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<a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a>; <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a>;
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<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p></dd><dt id="oligogenic">oligogenic</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> expressed only in the presence of pathogenic variants in more than one <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>; may be referred to (with less precision) as multigenic or <a class="def" href="/books/NBK5191/def-item/polygenic/">polygenic</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/digenic/">digenic</a>;
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<a class="def" href="/books/NBK5191/def-item/trigenic/">trigenic</a></p></dd><dt id="open-reading-frame">open reading frame</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/coding-region/">coding region</a>.</p></dd><h2 id="IX-P">P</h2><dt id="pathogenic-variant">pathogenic variant</dt><dd><p>An alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (distinct from the reference sequence) that is associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or increased disease risk. A pathogenic variant meets criteria to be
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classified as pathogenic according to the five-tier system for describing the clinical significance of genetic variants (see Related terms).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
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<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>;
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<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="pcr">PCR</dt><dd><p>
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Synonym: <a class="def" href="/books/NBK5191/def-item/polymerase-chain-reaction/">polymerase chain reaction</a>
|
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</p><p>A procedure that produces millions of copies of a short segment of DNA through repeated cycles of: (1) denaturation, (2) annealing, and (3) elongation. PCR is commonly used either:
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(a) to generate a sufficient quantity of DNA to perform a test (e.g., <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>); or (b) as a test in and of itself (e.g., <a class="def" href="/books/NBK5191/def-item/allele/">allele</a>-specific amplification, <a class="def" href="/books/NBK5191/def-item/trinucleotide-repeat/">trinucleotide repeat</a> quantification).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/quantitative-pcr/">quantitative PCR</a>; <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a>; <a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a></p></dd><dt id="pedigree">pedigree</dt><dd><p>A diagram of the genetic relationships and medical history of a family using standard symbols and terminology</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/consanguineous/">consanguineous</a>;
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<a class="def" href="/books/NBK5191/def-item/obligate-heterozygote/">obligate heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/proband/">proband</a></p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-154/?report=objectonly" target="object" rid-ob="figobfurtherillus154">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="penetrance">penetrance</dt><dd><p>The proportion of individuals with a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> causing a particular disorder who exhibit clinical findings of that disorder; most often refers to <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a> conditions.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/autosomal-dominant/">autosomal dominant</a>; <a class="def" href="/books/NBK5191/def-item/intrafamilial-variability/">intrafamilial variability</a>; <a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p></dd><dt id="phenotype">phenotype</dt><dd><p>The observable characteristics of the expression of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>; the clinical presentation of an individual with a particular <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allelic-heterogeneity/">allelic heterogeneity</a>; <a class="def" href="/books/NBK5191/def-item/dysmorphic/">dysmorphic</a>; <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a>; <a class="def" href="/books/NBK5191/def-item/genotype-phenotype-correlations/">genotype-phenotype correlations</a>; <a class="def" href="/books/NBK5191/def-item/variable-expressivity/">variable expressivity</a></p></dd><dt id="polygenic">polygenic</dt><dd><p>Referring to a condition caused by the additive contributions of variants in multiple genes at different loci</p></dd><dt id="polymerase-chain-reaction">polymerase chain reaction</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/sequence-analysis/">PCR</a>.</p></dd><dt id="polymorphism">polymorphism</dt><dd><p>A natural variation in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>, DNA sequence, protein, or <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> that has no adverse effect on the individual</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/allele/">allele</a>;
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<a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>; <a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a></p></dd><dt id="postzygotic">postzygotic</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> or abnormality in <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> replication/<a class="def" href="/books/NBK5191/def-item/segregation/">segregation</a>/<a class="def" href="/books/NBK5191/def-item/methylation/">methylation</a> that occurs after fertilization of the ovum by the sperm, often
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leading to <a class="def" href="/books/NBK5191/def-item/mosaicism/">mosaicism</a> (two or more genetically distinct cell lines within the same organism)</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a>;
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<a class="def" href="/books/NBK5191/def-item/mosaicism/">mosaicism</a>; <a class="def" href="/books/NBK5191/def-item/somatic-mosaicism/">somatic mosaicism</a>; <a class="def" href="/books/NBK5191/def-item/trisomy-rescue/">trisomy rescue</a></p></dd><dt id="preimplantation-genetic-diagnosis">preimplantation genetic diagnosis</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/preimplantation-genetic-testing/">preimplantation genetic testing</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>;
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<a class="def" href="/books/NBK5191/def-item/pcr/">polymerase chain reaction (PCR)</a>; <a class="def" href="/books/NBK5191/def-item/prenatal-testing/">prenatal testing</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="preimplantation-genetic-testing">preimplantation genetic testing</dt><dd><p>
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Synonyms: PGT, preimplantation testing
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</p><p>Genetic testing of one or more cells removed from early embryos conceived by in vitro fertilization and transferring to the mother's uterus only those embryos determined
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|
not to have the <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>(s)/<a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> anomaly(ies) of concern</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>;
|
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<a class="def" href="/books/NBK5191/def-item/pcr/">polymerase chain reaction (PCR)</a>; <a class="def" href="/books/NBK5191/def-item/prenatal-testing/">prenatal testing</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="premutation">premutation</dt><dd><p>An <a class="def" href="/books/NBK5191/def-item/allele/">allele</a> in which a tandemly repeated nucleotide sequence within or near a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> contains more repeats than a normal allele. A premutation allele can expand into a
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<a class="def" href="/books/NBK5191/def-item/full-penetrance-allele/">full-penetrance allele</a> (repeat size associated with disease) when passed through the <a class="def" href="/books/NBK5191/def-item/germline/">germline</a>. Although premutation alleles are not typically associated with disease,
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in rare instances they are; the best example is premutation <i>FMR1</i> alleles, which are associated with disease phenotypes distinct from fragile X syndrome
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(which is caused by full-penetrance <i>FMR1</i> alleles). </p></dd><dt id="prenatal-diagnosis">prenatal diagnosis</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/prenatal-testing/">prenatal testing</a>.</p></dd><dt id="prenatal-testing">prenatal testing</dt><dd><p>Testing performed during pregnancy. Prenatal testing may be used to determine if a fetus is affected with a
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particular disorder. Invasive procedures such as chorionic villus sampling (CVS), amniocentesis, or
|
|
periumbilical blood sampling (PUBS) are used to obtain a sample for testing; imaging (e.g., ultrasound, MRI)
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is used to evaluate fetal anatomy.</p></dd><dt id="private">private</dt><dd><p>Referring to a variant that does not have appreciable <a class="def" href="/books/NBK5191/def-item/allele-frequency/">allele frequency</a> in the general population; a private variant
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may be benign or pathogenic; historically used to describe a variant thought to occur in a single family</p></dd><dt id="proband">proband</dt><dd><p>
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Synonyms: propositus, index case
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|
</p><p>The affected individual through whom a family with a genetic disorder is ascertained; may or may not be the individual presenting for <a class="def" href="/books/NBK5191/def-item/genetic-counseling/">genetic counseling</a></p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/pedigree/">pedigree</a></p></dd><dt id="promoter-region">promoter region</dt><dd><p>A region of DNA (just upstream of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>) that acts as a binding site for transcription factors and RNA polymerase to initiate transcription</p></dd><dt id="pseudodominant-inheritance">pseudodominant inheritance</dt><dd><p>An <a class="def" href="/books/NBK5191/def-item/autosomal-recessive/">autosomal recessive</a> condition present in individuals in two or more generations of a family, thereby appearing to follow a dominant inheritance pattern; occurs as a
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result of reproduction between an affected individual and a <a class="def" href="/books/NBK5191/def-item/carrier/">carrier</a> partner</p></dd><dt id="pseudogene">pseudogene</dt><dd><p>A copy of a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> that is transcriptionally or translationally inactive due to accumulation of <a class="def" href="/books/NBK5191/def-item/inactivating/">inactivating</a> variants. Pseudogenes are classified as either non-processed
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(includes introns) or processed (does not include introns).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>;
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<a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>; <a class="def" href="/books/NBK5191/def-item/unequal-crossing-over/">unequal crossing over</a></p></dd><h2 id="IX-Q">Q</h2><dt id="quantitative-pcr">quantitative PCR</dt><dd><p>
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Synonyms: kinetic quantitative PCR, real time quantitative PCR
|
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</p><p>A form of <a class="def" href="/books/NBK5191/def-item/pcr/">PCR</a> used to determine the relative amount of DNA or RNA in a sample; commonly used to detect <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> deletions and duplications</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>;
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<a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>; <a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>;
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<a class="def" href="/books/NBK5191/def-item/pcr/">PCR</a>; <a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><h2 id="IX-R">R</h2><dt id="recombination">recombination</dt><dd><p>The exchange of a segment of DNA between two homologous chromosomes during meiosis leading to a novel combination of genetic material in the gamete</p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-186/?report=objectonly" target="object" rid-ob="figobfurtherillus186">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="recurrence-risk">recurrence risk</dt><dd><p>The likelihood that a trait or disorder present in one family member will occur again in other family members in the same or subsequent generations</p></dd><dt id="recurrent-deletion">recurrent deletion</dt><dd><p>Deletion of a specific size - usually mediated by <a class="def" href="/books/NBK5191/def-item/nonallelic-homologous-recombination/">nonallelic homologous recombination</a> (NAHR) - occurring multiple times in the general population</p><p>Related term:
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<a class="def" href="/books/NBK5191/def-item/nonallelic-homologous-recombination/">nonallelic homologous recombination</a>
|
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</p></dd><dt id="reduced-penetrance-allele">reduced-penetrance allele</dt><dd><p>An alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (distinct from the reference sequence) that is associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> or increased disease risk in some (not all)
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individuals who have the alteration</p></dd><dt id="revertant-mosaicism">revertant mosaicism</dt><dd><p>Presence of two or more cell lines in one individual that have different genetic compositions - one or more cell lines having a <a class="def" href="/books/NBK5191/def-item/germline/">germline</a> <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> and the other(s) derived from spontaneous somatic correction of the germline pathogenic variant to the normal (<a class="def" href="/books/NBK5191/def-item/wild_type/">wild type</a>) state</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/germline-variant/">germline variant</a>;
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<a class="def" href="/books/NBK5191/def-item/mosaicism/">mosaicism</a>; <a class="def" href="/books/NBK5191/def-item/somatic-mosaicism/">somatic mosaicism</a></p></dd><dt id="robertsonian-translocation">Robertsonian translocation</dt><dd><p>The joining of two acrocentric chromosomes at the centromeres with loss of their short arms to form a single abnormal <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>; in acrocentric chromosomes the centromere is located
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near the end of the chromosome. Acrocentric chromosomes are 13, 14, 15, 21, and 22.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a>;
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<a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a></p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-211/?report=objectonly" target="object" rid-ob="figobfurtherillus211">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><h2 id="IX-S">S</h2><dt id="sanger-sequencing">Sanger sequencing</dt><dd><p>A method of DNA sequencing that uses DNA polymerase to copy single-stranded DNA templates by adding nucleotides to form a complementary strand. Its use is limited to
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<a class="def" href="/books/NBK5191/def-item/sequence-analysis/">sequence analysis</a> of a single region of DNA (maximum ~1000 bp) - in contrast to massively parallel sequencing, in which millions of fragments of DNA can be sequenced simultaneously.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion-duplication-analysis/">deletion/duplication analysis</a>;
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<a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>; <a class="def" href="/books/NBK5191/def-item/pcr/">PCR</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="second-degree-relative">second-degree relative</dt><dd><p>A relative who shares one quarter of an individual's genes is shared (i.e., grandparent, grandchild, uncle, aunt, nephew, niece, half-sib)</p></dd><dt id="segregation">segregation</dt><dd><p>The separation of the homologous chromosomes and their random distribution to the gametes at meiosis</p></dd><dt id="sensitivity">sensitivity</dt><dd><p>The frequency with which testing yields a positive result when the individual being tested either (a) is actually affected (clinical sensitivity) or (b) has a <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>
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detected by <a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a> (analytic sensitivity)</p></dd><dt id="sequence-alteration">sequence alteration</dt><dd><p>
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Synonym: variant
|
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</p><p>Any alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> from its natural state; may be benign (may be referred to as a "<a class="def" href="/books/NBK5191/def-item/polymorphism/">polymorphism</a>"), pathogenic, or of <a class="def" href="/books/NBK5191/def-item/uncertain-significance/">uncertain significance</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
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<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>;
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|
<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a>;
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<a class="def" href="/books/NBK5191/def-item/uncertain-significance/">variant of uncertain significance</a>; <a class="def" href="/books/NBK5191/def-item/wild_type/">wild type</a></p></dd><dt id="sequence-analysis">sequence analysis</dt><dd><p>
|
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Synonym: sequencing
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</p><p>Process by which the nucleotide sequence for a segment of DNA is determined</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>;
|
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<a class="def" href="/books/NBK5191/def-item/next-generation-sequencing/">next-generation sequencing</a>; <a class="def" href="/books/NBK5191/def-item/pcr/">PCR</a>; <a class="def" href="/books/NBK5191/def-item/sanger-sequencing/">Sanger sequencing</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="simplex">simplex</dt><dd><p>Referring to a single occurrence of a disorder in a family</p></dd><dt id="single-nucleotide-variant">single-nucleotide variant</dt><dd><p>
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Synonyms: SNV, point mutation
|
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</p><p>An alteration in DNA sequence caused by a single-nucleotide base change, <a class="def" href="/books/NBK5191/def-item/insertion/">insertion</a>, or <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; can be benign, pathogenic, or of <a class="def" href="/books/NBK5191/def-item/uncertain-significance/">uncertain significance</a></p></dd><dt id="sister-chromatid-exchange">sister chromatid exchange</dt><dd><p>
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Synonym: SCE
|
|
</p><p>Exchange of genetic material between the two chromatids of a single <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> during the cell division process; similar to crossing over
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(<a class="def" href="/books/NBK5191/def-item/recombination/">recombination</a>), except that the exchange involves the two sister chromatids of a single chromosome, whereas crossing over refers to exchange
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of genetic material between the two homologous chromosomes of a chromosome pair</p></dd><dt id="snp-array">SNP array</dt><dd><p>Method used in a given individual to <a class="def" href="/books/NBK5191/def-item/genotype/">genotype</a> single-nucleotide polymorphisms (SNPs) across the genome to identify: (1) copy number variants;
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(2) regions of <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a>; (3) evidence of parental <a class="def" href="/books/NBK5191/def-item/consanguinity/">consanguinity</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a>;
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<a class="def" href="/books/NBK5191/def-item/comparative-genomic-hybridization/">comparative genomic hybridization</a>; <a class="def" href="/books/NBK5191/def-item/copy-number-variant/">copy number variant</a>;
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<a class="def" href="/books/NBK5191/def-item/single-nucleotide-variant/">single-nucleotide variant</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a>
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</p></dd><dt id="somatic-mosaicism">somatic mosaicism</dt><dd><p>Two or more cell lines with a different genetic composition within the cells of an individual (may or may not include the <a class="def" href="/books/NBK5191/def-item/germline/">germline</a> cells)</p><p>
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Related term:
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<a class="def" href="/books/NBK5191/def-item/gonadal-mosaicism/">gonadal mosaicism</a>
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</p></dd><dt id="somatic-pathogenic-variant">somatic pathogenic variant</dt><dd><p>Variant resulting from mutation that occurs during embryonic development (i.e., that is not inherited from a parent)</p></dd><dt id="southern-blot">Southern blot</dt><dd><p>
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Synonyms: Southern analysis, Southern blot analysis
|
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</p><p>Technique used to detect differences in the lengths of DNA fragments occurring as a result of a variant or <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> rearrangement</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>;
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<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="splice-site">splice site</dt><dd><p>The junction between an <a class="def" href="/books/NBK5191/def-item/intron/">intron</a> and an <a class="def" href="/books/NBK5191/def-item/exon/">exon</a> in a DNA sequence; the site of intron/exon <a class="def" href="/books/NBK5191/def-item/splicing/">splicing</a>. A variant in the splice site can cause abnormal removal of introns and
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splicing together of exons such that one or more introns remaining in the <a class="def" href="/books/NBK5191/def-item/mrna/">mRNA</a> can potentially disrupt generation of the protein product. </p></dd><dt id="splicing">splicing</dt><dd><p>The process by which introns (noncoding regions) are excised out of the primary messenger RNA transcript and exons (i.e., coding regions) are joined together to
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generate mature messenger RNA</p></dd><dt id="sporadic">sporadic</dt><dd><p>Referring to the chance occurrence of a disorder or abnormality that is not expected to recur in a family</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/recurrence-risk/">recurrence risk</a>;
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<a class="def" href="/books/NBK5191/def-item/simplex/">simplex</a></p><p>
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<a class="img_link" href="/books/NBK5191/box/further_illus-204/?report=objectonly" target="object" rid-ob="figobfurtherillus204">
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
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</a>
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</p></dd><dt id="syndromic">syndromic</dt><dd><p>In <i>GeneReviews</i>: referring to a disorder characterized by a constellation of phenotypic features that either:
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(1) specifically suggest the diagnosis (which can be confirmed by <a class="def" href="/books/NBK5191/def-item/molecular-genetic-testing/">molecular genetic testing</a>);
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or (2) allow diagnosis of the disorder in the absence of confirmatory molecular genetic findings</p></dd><h2 id="IX-T">T</h2><dt id="targeted-analysis-for-pathogenic-variants">targeted analysis for pathogenic variants</dt><dd><p>Testing for specific variants known to cause disease. Examples include: (1) one or more specific pathogenic variants (e.g., Glu6Val for sickle cell anemia,
|
|
a panel of pathogenic variants for cystic fibrosis); (2) a <a class="def" href="/books/NBK5191/def-item/nucleotide-repeat/">nucleotide repeat</a> expansion (e.g., the <a class="def" href="/books/NBK5191/def-item/trinucleotide-repeat/">trinucleotide repeat</a> expansion associated with Huntington
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disease); and (3) common deletions (e.g., population-specific alpha globin <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> deletions).</p></dd><dt id="targeted-mutation-analysis">targeted mutation analysis</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a>.</p></dd><dt id="trans">
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<i>trans</i>
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</dt><dd><p>
|
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Synonym: <i>trans</i> configuration
|
|
</p><p>Referring to two <a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> variants on opposite homologous chromosomes (typically used to describe variants within the same <a class="def" href="/books/NBK5191/def-item/gene/">gene</a>)</p><p>
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Related term:
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|
<a class="def" href="/books/NBK5191/def-item/cis/">
|
|
<i>cis</i>
|
|
</a>
|
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</p></dd><dt id="transcription-factor">transcription factor</dt><dd><p>A protein that binds to DNA and either activates or represses transcription of one or more genes</p></dd><dt id="translocation">translocation</dt><dd><p>
|
|
Synonym: <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> rearrangement
|
|
</p><p>A <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> alteration in which a whole chromosome or segment of a chromosome becomes attached to or interchanged with another whole chromosome or segment</p><p>Balanced translocations (in which there is no apparent net loss or gain of <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> material) are usually not associated with phenotypic abnormalities,
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|
although <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> disruptions at the breakpoints of the translocation can, in some cases, cause adverse effects, including some known genetic disorders.</p><p>Unbalanced translocations (in which there is loss or gain of <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> material) are nearly always associated with an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a>. </p><p>Balanced and unbalanced translocations can be visualized by <a class="def" href="/books/NBK5191/def-item/karyotype/">karyotype</a> analysis; <a class="def" href="/books/NBK5191/def-item/chromosomal-microarray/">chromosomal microarray</a> (CMA) cannot detect balanced translocations. </p></dd><dt id="trigenic">trigenic</dt><dd><p>Referring to expression of a <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> that requires the presence of pathogenic variants in three different genes</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/digenic/">digenic</a>; <a class="def" href="/books/NBK5191/def-item/oligogenic/">oligogenic</a></p></dd><dt id="trinucleotide-repeat">trinucleotide repeat</dt><dd><p>Sequences of three nucleotides repeated a number of times in tandem within a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a></p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/anticipation/">anticipation</a>;
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<a class="def" href="/books/NBK5191/def-item/nucleotide-repeat/">nucleotide repeat</a>; <a class="def" href="/books/NBK5191/def-item/premutation/">premutation</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/targeted-analysis-for-pathogenic-variants/">targeted analysis for pathogenic variants</a></p></dd><dt id="trisomy-rescue">trisomy rescue</dt><dd><p>The phenomenon in which a fertilized ovum initially contains 47 chromosomes (i.e., one <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> is trisomic), but loses one of the trisomic chromosomes in the process
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of cell division such that the resulting daughter cells and their descendants contain 46 chromosomes, the normal number</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/aneuploidy/">aneuploidy</a>;
|
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<a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>; <a class="def" href="/books/NBK5191/def-item/postzygotic/">postzygotic</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a></p><p>
|
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<a class="img_link" href="/books/NBK5191/box/disease_example-215/?report=objectonly" target="object" rid-ob="figobdiseaseexample215">
|
|
<span class="graphic"><img src="/books/NBK5191/bin/DiseaseExample.jpg" alt="Image DiseaseExample.jpg" /></span>
|
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</a>
|
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<a class="img_link" href="/books/NBK5191/box/further_illus-215/?report=objectonly" target="object" rid-ob="figobfurtherillus215">
|
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
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</p></dd><h2 id="IX-U">U</h2><dt id="uncertain-significance">uncertain significance</dt><dd><p>A variant of uncertain significance (VOUS, VUS) is an alteration in a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> (distinct from the reference sequence) that may or may not be disease-causing or associated with
|
|
increased risk of an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a>; the identification of a variant of uncertain significance neither confirms nor rules out a diagnosis. A variant of uncertain
|
|
significance does not meet criteria to be classified as pathogenic or benign according to the five-tier system for describing the clinical significance of genetic variants
|
|
(see Related terms). Sequence analysis may identify multiple variants of uncertain significance in a given gene or hundreds to thousands in the human <a class="def" href="/books/NBK5191/def-item/exome/">exome</a>.
|
|
</p><p>Related terms:
|
|
<a class="def" href="/books/NBK5191/def-item/benign-variant/">benign variant</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/likely-benign/">likely benign</a>; <a class="def" href="/books/NBK5191/def-item/likely-pathogenic/">likely pathogenic</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a></p></dd><dt id="unequal-crossing-over">unequal crossing over</dt><dd><p>Exchange of DNA during meiosis between improperly aligned segments of DNA that can result in a gain or loss of DNA. Circumstances that predispose to unequal crossing over are misalignment of: (1) highly homologous segment duplications (low copy repeats) referred to as <a class="def" href="/books/NBK5191/def-item/nonallelic-homologous-recombination/">nonallelic homologous recombination</a> which result in recurrent
|
|
deletions or duplications; and (2) a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> and its <a class="def" href="/books/NBK5191/def-item/pseudogene/">pseudogene</a> in tandem on a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> (e.g., <i>CYP21</i> and its pseudogene <i>CYP21P</i>;
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<i>GBA1</i> [formerly <i>GBA</i>] and its pseudogene <i>GBA1LP</i> [formerly <i>GBAP</i>]) which result in <a class="def" href="/books/NBK5191/def-item/de-novo/"><i>de novo</i></a> pathogenic variants. </p><p>See <a class="def" href="/books/NBK5191/def-item/nonallelic-homologous-recombination/">nonallelic homologous recombination</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/deletion/">deletion</a>; <a class="def" href="/books/NBK5191/def-item/duplication/">duplication</a>;
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|
<a class="def" href="/books/NBK5191/def-item/gene-conversion/">gene conversion</a>; <a class="def" href="/books/NBK5191/def-item/recombination/">recombination</a></p></dd><dt id="uniparental-disomy">uniparental disomy</dt><dd><p>
|
|
Synonym: UPD
|
|
</p><p>The situation in which both copies of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> pair (or chromosome pair segment) are from one parent (i.e., no copy is from the other parent). The individual may have two identical copies of one of the pair of parental chromosomes (termed <b><a class="def" href="/books/NBK5191/def-item/uniparental-isodisomy/">uniparental isodisomy</a></b>), or may have one copy of each of the parental chromosome pair (termed <b><a class="def" href="/books/NBK5191/def-item/uniparental-heterodisomy/">uniparental heterodisomy</a></b>). Uniparental disomy can result in an abnormal <a class="def" href="/books/NBK5191/def-item/phenotype/">phenotype</a> in some instances.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>; <a class="def" href="/books/NBK5191/def-item/trisomy-rescue/">trisomy rescue</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-heterodisomy/">uniparental heterodisomy</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-isodisomy/">uniparental isodisomy</a></p><p>
|
|
<a class="img_link" href="/books/NBK5191/box/further_illus-217/?report=objectonly" target="object" rid-ob="figobfurtherillus217">
|
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<span class="graphic"><img src="/books/NBK5191/bin/LearnMore.jpg" alt="Image LearnMore.jpg" /></span>
|
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</a>
|
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</p></dd><dt id="uniparental-heterodisomy">uniparental heterodisomy</dt><dd><p>The situation in which an individual inherits both copies of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> pair (or chromosome pair segment) from one parent; no copy is inherited from the other parent (compare <b><a class="def" href="/books/NBK5191/def-item/uniparental-isodisomy/">uniparental isodisomy</a></b>).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>; <a class="def" href="/books/NBK5191/def-item/trisomy-rescue/">trisomy rescue</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-isodisomy/">uniparental isodisomy</a></p></dd><dt id="uniparental-isodisomy">uniparental isodisomy</dt><dd><p>The situation in which an individual inherits two identical copies of one of a <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> pair (or chromosome pair segment) from one parent; no copy is inherited from the other parent (compare <b><a class="def" href="/books/NBK5191/def-item/uniparental-heterodisomy/">uniparental heterodisomy</a></b>).</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/imprinting/">imprinting</a>; <a class="def" href="/books/NBK5191/def-item/trisomy-rescue/">trisomy rescue</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-disomy/">uniparental disomy</a>; <a class="def" href="/books/NBK5191/def-item/uniparental-heterodisomy/">uniparental heterodisomy</a></p></dd><dt id="unknown-significance">unknown significance</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/uncertain-significance/">uncertain significance</a>.</p></dd><h2 id="IX-V">V</h2><dt id="variable-expressivity">variable expressivity</dt><dd><p>Variation in clinical features (type and severity) of a genetic disorder between affected individuals, even within the same family</p><p>Related terms:
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<a class="def" href="/books/NBK5191/def-item/interfamilial-variability/">interfamilial variability</a>;
|
|
<a class="def" href="/books/NBK5191/def-item/intrafamilial-variability/">intrafamilial variability</a></p></dd><h2 id="IX-W">W</h2><dt id="whole-exome-sequencing">whole-exome sequencing</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/exome-sequencing/">exome sequencing</a>.</p></dd><dt id="whole-genome-sequencing">whole-genome sequencing</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/genome-sequencing/">genome sequencing</a>.</p></dd><dt id="wild_type">wild type</dt><dd><p>Referring to a normal, fully functional <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> or <a class="def" href="/books/NBK5191/def-item/allele/">allele</a></p></dd><h2 id="IX-X">X</h2><dt id="x-chromosome-inactivation">X-chromosome inactivation</dt><dd><p>
|
|
Synonym: lyonization
|
|
</p><p>In females, the phenomenon by which one X <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> (either maternally or paternally derived)
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is randomly inactivated in early embryonic cells, with fixed inactivation in all descendant cells; first described by the geneticist Mary F Lyon, PhD.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/manifesting-heterozygote/">manifesting heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a></p></dd><dt id="x-linked">X-linked</dt><dd><p>Referring to a <a class="def" href="/books/NBK5191/def-item/gene/">gene</a> on the X <a class="def" href="/books/NBK5191/def-item/chromosome/">chromosome</a> or to the <a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a> in which the causative <a class="def" href="/books/NBK5191/def-item/pathogenic-variant/">pathogenic variant</a> is on the X chromosome; <a class="def" href="/books/NBK5191/def-item/hemizygous/">hemizygous</a> males will be affected;
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<a class="def" href="/books/NBK5191/def-item/heterozygous/">heterozygous</a> females may or may not be affected depending on the disorder and factors influencing <a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a>.</p><p>Related terms: <a class="def" href="/books/NBK5191/def-item/hemizygous/">hemizygous</a>;
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<a class="def" href="/books/NBK5191/def-item/heterozygote/">heterozygote</a>; <a class="def" href="/books/NBK5191/def-item/mode-of-inheritance/">mode of inheritance</a>; <a class="def" href="/books/NBK5191/def-item/x-chromosome-inactivation/">X-chromosome inactivation</a></p></dd><dt id="x-linked-dominant">X-linked dominant</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a>.</p></dd><dt id="x-linked-recessive">X-linked recessive</dt><dd><p>See <a class="def" href="/books/NBK5191/def-item/x-linked/">X-linked</a>.</p></dd></dl></div><div id="bk_toc_contnr"></div></div></div>
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