Partial Deficiency of Hypoxanthine-Guanine Phosphoribosyltransferase: Intermediate Enzyme Deficiency in Heterozygote Red Cells

Heterozygotes for hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) deficiency, although they demonstrate HGPRTase positive and negative cells on fibroblast culture, generally have normal activities of HGPRTase in erythrocyte hemolysates. We report a group of heterozygotes from a family with a partial deficiency of this enzyme, some of whom exhibit HGPRTase activity in red cell hemolysates that is less than two standard deviations below the normal mean and in whom the activity levels vary between 22% and 75% of normal. On the other hand, heterozygotes from another family with a severe deficiency of the enzyme all exhibited normal enzyme activities in red cell hemolysates. These observations are consistent with the hypothesis that the bone marrow is populated entirely by normal cells in heterozygotes for the severe deficiency but by various proportions of normal and partially deficient cells in heterozygotes for the partial deficiency.