A new variant of clinical galactosemia with two hitherto unidentified alleles on the transferase locus in one family is described. This new clinical variant of transferase has 25 of normal control activity in blood and in skin fibroblasts, and the patient accumulates galactose-1-phosphate in blood on an unrestricted galactose diet. Using starch gel electrophoresis on the hemolysate of the family members, a fast-moving transferase with mobility in between those of the normal control and of the Duarte variant is identified. This new allele is designated as$$GALT^{C_1 } $$(fast-moving Chicago variant). In addition, a second new allele was documented in this family by studying the instability of the transferase enzyme in hemolysates of family members at 50°C for various time intervals. This new allele is designated as$$GALT^{C_2 } $$(heat-labile Chicago variant). On the basis of the studies, the transferase genotype of this patients is thought to be a double heterozygote compound,$$GALT^{C_1 } $$/GALTG
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