Identification of a 7-Basepair Deletion in the Adenine Phosphoribosyl-Transferase Gene as a Cause of 2,8-Dihydroxyadenine Urolithiasis

We describe a family of Turkish origin with adenine phosphoribosyltransferase (APRT) deficiency and renal stone disease. The proband had 2,8-dihydroxyadenine urolithiasis but an older sister, who was also deficient in enzyme activity, is so far asymptomatic. The proband was homozygous for a 7-bp deletion in exon 3 of the APRT gene. One allele from each of the parents also contained this deletion. The patient and her father were homozygous for an intragenic TaqI RFLP (1.25-kb fragment) whereas the mother was heterozygous (1.25- and 1.91-kb fragments), indicating that the mutation was present on the allele carrying the 1.25 kb TaqI fragment. The deletion alters the reading frame downstream of codon 93 and would be expected to abolish enzyme activity