Biochemical genetics of HPRT Cape Town: is the defect in the HPRT gene?

HPRT Cape Town shows low levels of purine salvage in cultured cells which is associated with the unusual property of substrate inhibition by its purine substrates in erythrocyte haemolysates. Since it is not certain that the defect is in the HPRT gene, we studied enzyme kinetics in cell-free preparations of erythrocytes and transformed lymphoblasts from both the proband and his obligate heterozygote daughter and studied purine salvage in intact cells. Substrate inhibition was demonstrated in erythrocyte and lymphoblast cell-free extracts from the proband and his daughter and lymphoblasts from the daughter showed similar growth properties in selective media to her father. These results were all consistent with the defect being in the HPRT gene.