Genetic basis of galactosemia

Classic galactosemia is an inborn error of galactose metabolism and results from deficiency of the ubiquitously expressed enzyme galactose‐1‐phosphate uridyltransferase (GALT). Nine missense mutations, three splicing mutations, three GALT protein polymorphisms, and one silent nucleotide substitution have been identified to data. Most of the disease‐causing mutations are rare among patients. The most common mutation, Q188R, has a frequency of only one‐fourth in the patient population examined. Three classes of disease‐causing mutations have been reported: CRM + missense mutations (the most common class), CRM − missense mutations, and splicing mutations. Thus, galactosemia is heterogeneous at the molecular level, which is noteworthy in light of the well‐documented clinical variability observed in this disorder. It has also been shown that eight of nine galactosemia missense mutations occur in evolutionarily well‐conserved domains, suggesting that they affect functionally and/or structurally important residues. In contrast, all protein polymorphisms alter variable amino acids which presumably are not important for the enzyme's function. © 1992 Wiley‐Liss, Inc.