Lesch-Nyhan syndrome: Absence of the mutant enzyme in erythrocytes of a heterozygote for both normal and mutant hypoxanthine-guanine phosphoribosyl transferase

Abstract

Subjects heterozygous for the Lesch-Nyhan syndrome with a deficiency of the X-linked gene for the enzyme hypoxanthine-guanine phosphoribosyl transferase (PRT) would be expected to have two populations of erythrocytes in roughly equal proportions—one type with the normal enzyme and the other type exhibiting the mutant form of the enzyme. In contrast to this prediction, previous studies utilizing an X-linked gene for another enzyme as a marker for the PRT locus have suggested that erythrocytes from heterozygotes consist largely of cells with the normal form of the enzyme. We have recently described a mutant form of hypoxanthine-guanine phosphoribosyl tranferase with altered kinetic properties which allow it to be measured in artificial mixtures with the normal enzyme. The mutant enzyme could not be detected in erythrocyte lysates from a proven heterozygote for both the normal and this mutant form of the enzyme. This provides additional evidence that either inactivation of the X-chromosome in erythropoietic tissue from the heterozygote for PRT deficiency is not random or that random X-chromosome inactivation is followed by selection against erythrocyte precursors with the mutant enzyme.