THE HUMAN GALACTOSE-1-PHOSPHATE URIDYLTRANSFERASE GENE

Classical galactosemia is an inborn error of metabolism caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT). Standard treatment with dietary galactose restriction will reverse the potentially lethal symptoms of the disease that are manifest in the newborn period. However, the long-term prognosis for these patients is variable. As a first step toward investigating the molecular basis for phenotypic variation in galactosemia, we have cloned and sequenced the entire gene for human galactose-1-phosphate uridyltransferase. This gene is organized into 11 exons spanning 4 kb. In exons 6,9, and a portion of 10, there is a high degree of amino acid sequence conservation among Escherichia coli, yeast, mouse, and human. We have identified a number of nucleotide changes in the GALT genes of galactosemic patients that alter conserved amino acids. The most common of these is an A to G transition at nucleotide position 1470, converting a glutamine to an arginine at amino acid codon position 188 (Q188R). Q188R is located in exon 6 in close proximity to the putative enzyme catalytic site and was found in over 60% of galactosemia alleles tested. © 1992 Academic Press, Inc. All rights reserved.