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<span>What do geneticists mean by anticipation?</span>
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<h1>What do geneticists mean by anticipation?</h1>
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<section><div class="mp-content"><p>The signs and symptoms of some genetic conditions tend to become more severe and appear at an earlier age as the disorder is passed from one generation to the next. This phenomenon is called anticipation. Anticipation is most often seen with certain genetic disorders of the nervous system, such as<a data-pid="14419" href="https://medlineplus.gov/genetics/condition/huntingtons-disease/"> Huntington's disease</a>, <a data-pid="14409" href="https://medlineplus.gov/genetics/condition/myotonic-dystrophy/">myotonic dystrophy</a>, and <a data-pid="14513" href="https://medlineplus.gov/genetics/condition/fragile-x-syndrome/">fragile X syndrome</a>.</p>
<p>Anticipation typically occurs with disorders that are caused by an unusual type of variant (mutation) called a trinucleotide repeat expansion. A trinucleotide repeat is a sequence of three <a data-pid="20107" href="https://medlineplus.gov/genetics/understanding/basics/dna/">DNA building blocks</a> (nucleotides) that is repeated a number of times in a row. DNA segments with an abnormal number of these repeats are unstable and prone to errors during cell division. The number of repeats can change as the gene is passed from parent to child. If the number of repeats increases, it is known as a trinucleotide repeat expansion. In some cases, the trinucleotide repeat may expand until the gene stops functioning normally. This expansion causes the features of some disorders to become more severe with each successive generation.</p>
<p>Most genetic disorders have signs and symptoms that differ among affected individuals, including affected people in the same family. Not all of these differences can be explained by anticipation. A combination of genetic, environmental, and lifestyle factors is probably responsible for the variability, although many of these factors have not been identified. Researchers study multiple generations of affected family members and consider the genetic cause of a disorder before determining that it shows anticipation.</p></div>
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<section><div class="side-section"><div class="mp-content"><div class="section-header long-header"><h2>For more information about anticipation:</h2></div><div class="section-body"><p>The Merck Manual Professional Version provides a brief explanation of anticipation as part of its chapter on <a href="https://www.merckmanuals.com/professional/special-subjects/general-principles-of-medical-genetics/dna-variants-and-mutations" rel="noopener noreferrer" target="_blank">nontraditional inheritance</a>.</p>
<p>The Myotonic Dystrophy Foundation describes <a href="https://www.myotonic.org/digital-academy/dm-anticipation-part-1" rel="noopener noreferrer" target="_blank">anticipation in the context of myotonic dystrophy</a>. </p></div></div>
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<section><div class="mp-exp mp-content"><h2>Topics in the Inheriting Genetic Conditions chapter</h2><ul><li><a data-pid="20159" href="https://medlineplus.gov/genetics/understanding/inheritance/runsinfamily/">What does it mean if a disorder seems to run in my family?</a></li><li><a data-pid="20161" href="https://medlineplus.gov/genetics/understanding/inheritance/familyhistory/">Why is it important to know my family health history?</a></li><li><a data-pid="20163" href="https://medlineplus.gov/genetics/understanding/inheritance/inheritancepatterns/">What are the different ways a genetic condition can be inherited?</a></li><li><a data-pid="20165" href="https://medlineplus.gov/genetics/understanding/inheritance/riskassessment/">If a genetic disorder runs in my family, what are the chances that my children will have the condition?</a></li><li><a data-pid="20167" href="https://medlineplus.gov/genetics/understanding/inheritance/penetranceexpressivity/">What are reduced penetrance and variable expressivity?</a></li><li>What do geneticists mean by anticipation?</li><li><a data-pid="20171" href="https://medlineplus.gov/genetics/understanding/inheritance/updimprinting/">What are genomic imprinting and uniparental disomy?</a></li><li><a data-pid="20173" href="https://medlineplus.gov/genetics/understanding/inheritance/chromosomalinheritance/">Are chromosomal disorders inherited?</a></li><li><a data-pid="20175" href="https://medlineplus.gov/genetics/understanding/inheritance/ethnicgroup/">Why are some genetic conditions more common in particular ethnic groups?</a></li><li><a data-pid="20177" href="https://medlineplus.gov/genetics/understanding/inheritance/heritability/">What is heritability?</a></li></ul><p><a data-pid="20081" href="https://medlineplus.gov/genetics/understanding/">Other chapters in Help Me Understand Genetics</a></p></div>
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