Xanthinuria type I is a rare disorder of purine metabolism caused by xanthine oxidoreductase or dehydrogenase (XDH) deficiency. We report a family with two affected children out of 335 pediatric stone patients studied since 1991 in Armenia. The propositus, a 13-month-old boy, presented with abdominal pain and urinary retention followed by stone passage (0.9x0.6 cm). Infrared spectroscopy in Yerevan revealed a pure xanthine stone. Family examination in the parents and brother was normal, but the propositus and his 8-year-old asymptomatic sister had hypouricemia, hypouricosuria, and high urinary excretion of hypoxanthine and xanthine. Ultrasonography in the index patient showed bilateral stones requiring pyelolithotomy. High fluid intake and purine restriction did not prevent further stone passages. The affected asymptomatic sister had a small pelvic stone (4 mm). Mutation analysis revealed a heterozygous novel base pair substitution in exon 25 of the XDH gene (c.2810C>T), resulting in an amino acid substitution (p.Thr910Met). The second mutation could not be detected. Despite this, the heterozygous mutation, the chemical findings, and the positive allopurinol test altogether prove xanthinuria type I, which may present wide clinical intrafamilial variation. Diagnosis is suspected usually from low serum uric acid. No specific therapy is available.

To study prospectively the risk factors and etiology of urolithiasis in all stone patients aged <15 years admitted from 1991 to 1999 to the Arabkir hospital in Yerevan. Stones were obtained by surgery (64%), extracorporeal shockwave lithotripsy (ESWL) (7%) or cystoscopic extraction (4%); 25% passed spontaneously. All were examined by infrared spectroscopy, and spot urines were analyzed chemically. 198 patients, 180 (68% males) with renal stones and 18 (83% males) with primary bladder stones, were studied. Calcium oxalate (CaOx) was the predominant constituent in 62% of the kidney stones, followed by struvite (17%), calcium phosphate (7%), uric acid (7%), ammonium acid urate (5%), and cystine (2%). Bladder stones contained CaOx in 72%, uric acid in 22% and ammonium acid urate in 6% of patients. Etiology was obviously metabolic in 5% and possibly metabolic in 26%. Twenty percent of stones were infectious, and 19% were endemic (9% bladder and 10% kidney stones); 4% were secondary to urinary stasis with malformation but no infection. Etiology in 26% remained unknown. Stone composition and metabolic etiology are similar to that in central Europe and North America. In contrast, infectious calculi and particularly endemic stones are still common, although becoming less so now. Urolithiasis in Armenia thus reflects the transition from a rural to an urban society.