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Title: Molecular basis for Duarte and Los Angeles variant galactosemia

Human erythrocytes that are homozygous for the Duarte enzyme variant of galactosemia (D/D) have a characteristic isoform on isoelectric focusing and 50% reduction in galactose-1-phosphate uridyltransferase (GALT) enzyme activity. The Duarte biochemical phenotype has a molecular genotype of N314D/N314D. The characteristic Duarte isoform is also associated with a variant called the {open_quotes}Los Angeles (LA) phenotype,{close_quotes} which has increased GALT enzyme activity. We evaluated GALT enzyme activity and screened the GALT genes of 145 patients with one or more N314D-containing alleles. We found seven with the LA biochemical phenotype, and all had a 1721C{r_arrow}T transition in exon 7 in cis with the N314D missense mutation. The 1721C{r_arrow}T transition is a neutral polymorphism for leucine at amino acid 218 (L218L). In pedigree analyses, this 1721C{r_arrow}T transition segregated with the LA phenotype of increased GALT activity in three different biochemical phenotypes (LA/N, LA/G, and LA/D). To determine the mechanism for increased activity of the LA variant, we compared GALT mRNA, protein abundance, and enzyme thermal stability in lymphoblast cell lines of D and LA phenotypes with comparable genotypes. GALT protein abundance was increased in LA compared to D alleles, but mRNA was similar among all genotypes. We conclude that the codon change N314Dmore » in cis with the base-pair transition 1721C{r_arrow}T produces the LA variant of galactosemia and that this nucleotide change increases GALT activity by increasing GALT protein abundance without increasing transcription or decreasing thermal lability. A favorable codon bias for the mutated codon with consequently increased translation rates is postulated as the mechanism. 23 refs., 3 figs., 4 tabs.« less
Authors:
; ;  [1]
  1. Emory Univ. School of Medicine, Atlanta, GA (United States) [and others
Publication Date:
OSTI Identifier:
518515
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Journal of Human Genetics; Journal Volume: 60; Journal Issue: 2; Other Information: PBD: Feb 1997
Country of Publication:
United States
Language:
English
Subject:
55 BIOLOGY AND MEDICINE, BASIC STUDIES; PATIENTS; HEREDITARY DISEASES; METABOLIC DISEASES; PHENOTYPE; GENOTYPE; GENETICS; ENZYMES; GENE MUTATIONS; ENZYME ACTIVITY; TRANSCRIPTION; DNA SEQUENCING; CODONS; PROTEINS; POLYMERASE CHAIN REACTION