X-linked hypoxanthine-guanine phosphoribosyl transferase deficiency: heterozygote has two clonal populations.

Clones of skin fibroblasts cultured from the mother of two sons with X-linked hypoxanthine-guanine phosphoribosyl transferase deficiency (Lesch-Nyhan syndrome) were assayed for activity of this enzyme by measurement of the incorporation of (3)H-guanine into guanylic acid as counts per minute per microgram of protein and by autoradiography. The demonstration of two populations of clones, wild-type clones with normal enzyme activity and mutant clones unable to incorporate (3)H-guanine, is evidence that the locus for hypoxanthineguanine phosphoribosyl transferase on one of the X chromosomes is inactive.