Introduction: 2,8-Dihydroxyadenine (DHA) urolithiasis is a rare type of urinary stone disease secondary to deficiency of adenine phosphoribosyltransferase (APRT) activity, a rare, inherited autosomal recessive disease with an incidental rate from 0.4 to 1.2%. The prevalence is higher among Japanese than other ethnic groups. APRT normally catalyzes the conversion of adenine to adenosine monophosphate and its deficiency results in 2,8-dihydroxyadenine (2,8-DHA) accumulation. This compound is extremely insoluble and its crystallization can lead to stone formation and renal failure. We report the case of 2,8-dihydroxyadenine (DHA) urolithiasis in a 52-year-old male patient.

Material and methods: In December 2008 a 52-year-old Caucasian man was admitted to our hospital with sudden pain in the left lumbar region. Abdominal X-ray did not show any radiopaque urinary stone. I.V. pielography showed a radiolucent left lumbar ureteral (0.6 mm) and renal (1.5 cm) stone. After therapy with tamsulosin, the ureteral stone was excreted. Successful ESWL treatment was performed for renal stone. He presented a clinical history of several episodes of bilateral renal colic and two prior ESWL treatment for radiolucent stones. Chemolitholysis was never successful. RESULTS. Stone analysis by infrared spectroscopy and microscopic examination of urine reveal typical 2,8-DHA crystals. APRT deficiency was detected in the hemolysate of erythrocyte. Partial deficiency of APRT in the patient's relatives showed heterozygosity of the enzyme defect. Allopurinol therapy successfully prevented further stone formation. 20 months later the patient remains stone free.

Conclusion: Two types of deficit are commonly distinguished, depending on the level of residual APRT activity. Type I is complete enzyme deficiency. Type II shows residual activity in cell lysates, but enzyme activity is not demonstrable in intact cells. About 78% of the Japanese patients belong to type II. The diagnosis of the disease is based on stone analysis by infrared spectroscopy or microscopic examination of urine, which may reveal typical 2,8-DHA crystals. Molecular approach can identify mutations, which are responsible of this inherited disease. Excessive water intake, restriction of foods with high adenine contents and administration of allopurinol are useful treatments. APRT deficiency is a rare disease but we can consider this pathology in case of recurrent radiolucent stones after chemolitolysis.