We describe a 2-year-old Japanese boy with radiolucent urolithiasis and recurrent urinary tract infection. Urinalysis showed typical 2,8-dihydroxyadenine (2,8-DHA) crystals, leading to a diagnosis as adenine phosphoribosyltransferase (APRT) deficiency. The sensitivity of proliferating T cells to an adenine analogue, whose cytotoxicity is dependent on APRT, showed that he was homozygous or compound heterozygous for the APRT gene mutation. A genetic analysis revealed a compound heterozygous state for M136T and a novel missense mutation L33P, not previously reported in patients with APRT deficiency.
Conclusion: Adenine phosphoribosyltransferase deficiency should be suspected in all patients with radiolucent kidney stones, urinary 2,8-DHA crystals were an important finding for an early diagnosis of APRT deficiency. Appropriate treatment should be initiated to prevent the development of urolithiasis or renal failure in APRT-deficient children. The T cell method was useful to detect a homozygote or a compound heterozygote of the pathogenic allelic gene in APRT deficiency, and a genetic analysis revealed a novel mutation L33P.