Blood sample obtained from a girl of 7 years old who received a diagnosis of urolithiasis of 2,8-dihydroxyadenine was subjected for enzymological studies on purine nucleotide biosynthesis including APRTase, HGPRTase, PRPPsynthetase.
APRTase activity in erythrocyt e s was 0.45nmoles/mg prot. /hr (2.5 per cent of normal) in the patient, and 4.75, 3.94, 6.20nmoles/mg prot. /hr (ranging from 20 to 31 per cent of norm al) in her clinically healthy brother, father and mother respectively. But HGPRTase activity in erythrocytes was 73.2, 70.0 nmoles/mg prot/hr (within normal range) and PRPPsynthetase activity in erythrocytes was 36.0,31.8 nmoles/mg prot. /hr (within normal range) in the patient and her mother respectively.
These findings suggested that the patient is homozygote and families are heterozygotes for this enzyme defect and the expression in phenotype is variable. In this case, however, the possibility of acceleration of IMP production is not excluded, because PRPP concentration in erythrocytes is thought to be elevated than that of normal subjects.
This possibility is now under investigation using high performance liquid chromatography.
