Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2009 May 1;18(9):1624-32.
doi: 10.1093/hmg/ddp080. Epub 2009 Feb 18.

Origins, distribution and expression of the Duarte-2 (D2) allele of galactose-1-phosphate uridylyltransferase

Amanda E Carney  1 , Rebecca D Sanders, Kerry R Garza, Lee Anne McGaha, Lora J H Bean, Bradford W Coffee, James W Thomas, David J Cutler, Natalie L Kurtkaya, Judith L Fridovich-Keil
Affiliations

Origins, distribution and expression of the Duarte-2 (D2) allele of galactose-1-phosphate uridylyltransferase

Amanda E Carney et al. Hum Mol Genet. .

Abstract

Duarte galactosemia is a mild to asymptomatic condition that results from partial impairment of galactose-1-phosphate uridylyltransferase (GALT). Patients with Duarte galactosemia demonstrate reduced GALT activity and carry one profoundly impaired GALT allele (G) along with a second, partially impaired GALT allele (Duarte-2, D2). Molecular studies reveal at least five sequence changes on D2 alleles: a p.N314D missense substitution, three intronic base changes and a 4 bp deletion in the 5' proximal sequence. The four non-coding sequence changes are unique to D2. The p.N314D substitution, however, is not; it is found together with a silent polymorphism, p.L218(TTA), on functionally normal Duarte-1 alleles (D1, also called Los Angeles or LA alleles). The HapMap database reveals that p.N314D is a common human variant, and cross-species comparisons implicate D314 as the ancestral allele. The p.N314D substitution is also functionally neutral in mammalian cell and yeast expression studies. In contrast, the 4 bp 5' deletion characteristic of D2 alleles appears to be functionally impaired in reporter gene transfection studies. Here we present allele-specific qRT-PCR evidence that D2 alleles express less mRNA in vivo than their wild-type counterparts; the difference is small but statistically significant. Furthermore, we characterize the prevalence of the 4 bp deletion in GG, NN and DG populations; the deletion appears exclusive to D2 alleles. Combined, these data strongly implicate the 4 bp 5' deletion as a causal mutation in Duarte galactosemia and suggest that direct tests for this deletion, as proposed here, could enhance or supplant current tests, which define D2 alleles on the basis of the presence and absence of linked coding sequence polymorphisms.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
Proposed origins and relationship of the p.N314, D1 and D2 alleles of human GALT. The predicted ancestral human GALT allele carries the (GTCA)3 + p.L218(CTA) + p.D314 sequences found in other hominid species. The p.D314N substitution occurs early in human evolution, and the 4 bp 5′ deletion and p.L218(TTA) silent substitution occur later, on distinct branches of the tree. The three intronic base changes reported to exist in cis with D2 alleles [c.378-27G>C or IVS4-27G > C, c.508-24G > A or IVS5-24G > A and c.507 + 62G > A or IVS5-62G > A (–22), not illustrated here] presumably occurred subsequent to, or concurrently with, the 4 bp 5′ deletion on the D2 branch of the tree.
Figure 2.
Figure 2.
Strategy for allele-specific amplification of (GTCA)2 versus (GTCA)3 5′ GALT sequences. As illustrated, the forward primer specific for the (GTCA)3 allele includes a 91 bp ‘tail’ of S. cerevisiae sequence that increases the size of the corresponding amplicon.
Figure 3.
Figure 3.
Multiplex allele-specific amplification of (GTCA)2 and (GTCA)3 5′ GALT sequences. (A) Amplification of (GTCA)2/(GTCA)2 and (GTCA)3/(GTCA)3 templates demonstrates the specificity of the primer sets. (B) A dilution series of template levels establishes the tolerance of both amplification reactions to a wide range of template concentrations.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Fridovich-Keil J., Walter J. Galactosemia. In: Valle D., Beaudet A.L., Vogelstein B., Kinzler K.W., Antonarakis S.E., Ballabio A., editors. The Online Metabolic and Molecular Bases of Inherited Disease—OMMBID. Chapter 72. New York: McGraw-Hill; 2008.
    1. Ficicioglu C., Yager C., Segal S. Galactitol and galactonate in red blood cells of children with the Duarte/galactosemia genotype. Mol. Genet. Metab. 2005;84:152–159. - PubMed
    1. Ficicioglu C., Thomas N., Yager C., Gallagher P., Hussa C., Mattie A., Day-Salvatore D., Forbes B. Duarte (DG) galactosemia: a pilot study of biochemical and neurodevelopmental assessment in children detected by newborn screening. Mol. Genet. Metab. 2008;95:206–212. - PubMed
    1. Suzuki M., West C., Beutler E. Large-scale molecular screening for galactosemia alleles in a pan-ethnic population. Hum. Genet. 2001;109:210–215. - PubMed
    1. Beutler E., Baluda M.L., Sturgeon P., Day R.W. A new genetic abnormality resulting in galactose-1-phosphate uridyltransferase deficiency. Lancet. 1965;1965–1961:353–354. - PubMed

Publication types

Substances