Adenine Phosphoribosyltransferase Deficiency: A Rare Cause of Recurrent Urolithiasis

Recurrent urolithiasis is troublesome for both patient and clinician, and in most cases, an underlying cause is not found. An important and underdiagnosed cause is adenine phosphoribosyltransferase (APRT) deficiency that gives rise to 2,8-dihydroxyadenine (2,8-DHA) stones. If diagnosed early, patient morbidity as well as the financial cost of treating stone recurrence can be avoided with simple medical therapy. A 36-year-old white, Caucasian male with recurrent urolithiasis was found to have 2,8-DHA stones. This was difficult to manage, as these stones were often large, bilateral, matrix in structure, and translucent on plain X-rays. He underwent a multitude of interventions including both retrograde and anterograde endoscopic approaches as well as extracorporeal shock wave lithotripsy. The specific stone type was eventually discovered through infrared spectroscopy and he was promptly commenced on allopurinol, which significantly improved his stone burden and frequency of presentation with renal colic. APRT deficiency is underdiagnosed given the estimated prevalence of 1/50,000-1/100,000, however, with less than 300 reported cases worldwide. This is likely because of both a lack of awareness of the disorder among clinicians and the challenges of identifying 2,8-DHA stones. Increasing awareness of 2,8-DHA urolithiasis among urologists as well as physicians is, therefore, key in tackling this condition.