Phenotypic expression of galactokinase deficiency in heterozygous and homozygous subjects: in vivo and in vitro studies.

Cultured fibroblasts derived from a patient homozygous for galactokinase deficiency, his parents, and controls had similar rates of growth in culture media where the only hexose was glucose. However, in media where the only hexose was galactose there was almost no growth of homozygous mutant cells or of maternal heterozygous cells and slight growth of paternal heterozygous cells. Growth of control cells was initially slow, but after a lag period (which coincided with increasing galactokinase activity) growth reached approximately the same levels as in glucose medium. In all cell lines there was a direct relation between the degree of enhancement of galactokinase activity and the ability of cells to adapt to growth in media where the only hexose was galactose. Erythrocyte galactokinase activities in a series of 24 children children with congenital cataracts aged 2-16 years were similar to those in 26 controls. One child in each of the cataract and control groups had 40-50% of mean control activity and was considered to be a potential heterozygote. Galactokinase deficiency (homozygous and heterozygous) is considered to be an uncommon cause of childhood cataracts. Nevertheless, it is an important cause since early dietary treatment can prevent or reverse lens opacities. The heterozygous state may be expressed phenotypically in the patient by the appearance of cataracts and in cultured cells by their defective growth in media where galactose is the only hexose.