A MOLECULAR APPROACH TO GALACTOSEMIA

Classical galactosemia (G/G) is caused by the lack of galactose-1-phos phate uridyltransferase (GALT) activity. A more common clinical varian t, Duarte/Classical (D/G) produces partial enzymatic impairment. Altho ugh neonatal death due to G/G galactosemia has been largely eliminated by population-based screening and intervention, long-term outcome in some is associated with impaired growth, ovarian failure, dyspraxic sp eech and neurologic deficits. At least 32 variants in the nucleotide s equence of the GALT gene have been identified and 9 have transferred i mpaired GALT activity to transformed cells in transfection experiments . We here define the prevalence and biochemical phenotype of two mutat ions. An A to G transition in exon 6 of the GALT gene converts a predi cted glutamine at codon 188 to an arginine (Q188R), and introduces a n ew HpaII cut site into the gene which enables population screening by polymerase chain reaction. An A to G transition in exon 10 in the GALT gene produces a codon change converting an asparagine to aspartic aci d at codon 314 (N314D) and adds an AVA II cut site. We screened a larg e population for the Q188R and N314D sequence changes to investigate t he prevalence of Q188R in G/G galactosemia, the effect of homozygosity for Q188R on outcome, and the prevalence and biochemical phenotype of the N314D sequence change. We found that the Q188R mutation has a pre valence of 62% in a predominately Caucasian population of 107 patients with G/G galactosemia. Homozygosity for Q188R was associated with a p oor clinical outcome in a subgroup of these patients. The N314D mutati on is associated with the Duarte biochemical phenotype with extraordin ary concordance.