Urinary stones resembling uric acid stones

A 52-year-old man was referred for the evaluation of mild renal failure with severe hypertension (220/130mmHg), which was resistant to combination therapy of a calcium channel blocker and an angiotensin II receptor blocker. Although he reported no past history indicating urolithiasis, urinalysis revealed plenty of round brownish stones (Figure 1A). The stones resembled uric acid (UA) stones (Figure 1B), but most of them had spicules radiating from the centre and rough surface, which are not prominent in UA stones. Furthermore, the stones were friable compared with UA stones. From these characteristics, the stones were recognized as 2,8-dihydroxyadenine (2,8-DHA) stones [1,2]. The diagnosis of type II adenine phosphoribosyltransferase (APRT) deficiency was confirmed by the genomic analysis that revealed APRT*J homozygote (Figure 2) [3]. The treatment by allopurinol with a low purine and low sodium diet diminished the stones and reduced the systemic blood pressure to 140/80mmHg. In APRT deficiency, the oxidation to 2,8-DHA is the met-