Hereditary xanthinuria in 2 Pakistani sisters: asymptomatic in one with beta-thalassemia but causing xanthine stone, obstructive uropathy and hypertension in the other.

We describe a 3-year-old Pakistani girl who presented with recurrent urinary infections. She had a nonfunctioning hydronephrotic right kidney and hypertension. At operation a calculus was impacted in the right ureter with dilatation of the pelviocaliceal system. Nephrectomy was performed. Histology revealed end stage pyelonephritis. The calculus consisted of pure xanthine. Further investigations demonstrated low serum uric acid and absent urinary uric acid with increased excretion of xanthine. Eight months after nephrectomy blood pressure had decreased to normal. Her 5-year-old sister, who has beta-thalassemia, also has a low serum uric acid concentration and xanthinuria. The treatment of choice is to increase fluid intake so that the urine xanthine concentration remains below the level at which xanthine crystallizes. This may require adjustment of the urine pH.