title: Characterization of patients with heterozygous cystinuria.
abstract: OBJECTIVE
  To characterize a contemporary cohort of patients with heterozygous (TZ) cystinuria and compare them with a concurrent cohort of patients with homozygous (MZ) cystinuria.
  
  
  METHODS
  A retrospective review of prospectively collected data was performed for 42 consecutive patients presenting with a positive cyanide-nitroprusside test from September 2009 to September 2011. Clinical data were collected, including the findings from a detailed metabolic stone workup that included two 24-hour urine collections with quantitative cystine. The patients were divided into 2 groups: those with TZ (30-400 mg/d) and those with MZ (>400 mg/d) cystinuria.
  
  
  RESULTS
  One patient was excluded because the cystine excretion was within the normal range (<30 mg/d), 35 (83.3%) and 6 (14.3%) had TZ and MZ cystinuria, respectively. Compared with those with TZ cystinuria, those with MZ cystinuria were significantly younger at the first stone episode (median 48 years, range 14-67, vs 17, range 6-44, P = .002), more were female (20% vs 66.7%; P = .03), and more patients had bilateral stones (8.6% vs 50%; P = .03). Finally, the patients with MZ cystinuria had more stone episodes than those with TZ cystinuria (3 vs 1; P = .04). From the detailed metabolic stone evaluation, the incidence of hyperuricemia was significantly greater in the MZ patients (17.1% vs 66.7%; P = .02). Although all the MZ patients developed pure cystine stones, 18 (51.4%), 7 (20.0%), and 3 (8.6%) of the TZ patients developed calcium oxalate, uric acid, and cystine stones, respectively (P < .001). In the TZ group, 11 patients (31.4%) had false-negative results on subsequent cyanide-nitroprusside testing.
  
  
  CONCLUSIONS
  Significant differences were found between the patients with TZ and MZ cystinuria in terms of age at the first stone episode, male/female ratio, incidence of hyperuricemia, and stone composition. The clinical significance remains to be elucidated.
authors.affiliation: Division of Urology, Department of Surgery, McGill University Health Centre, McGill University, Montreal, Quebec, Canada.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Elkoushy
authors.forename: Sero
authors.initials: S
authors.lastname: Andonian
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002129:Calcium Oxalate / Q000032:analysis; D002648:Child; D003553:Cystine / Q000032:analysis; D003555:Cystinuria / Q000235:genetics* / Q000652:urine*; D017050:Episode of Care; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D006962:Hyperparathyroidism, Secondary / Q000235:genetics; D033461:Hyperuricemia / Q000235:genetics; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012189:Retrospective Studies; D012737:Sex Factors; D018709:Statistics, Nonparametric; D014527:Uric Acid / Q000032:analysis; D014545:Urinary Calculi / Q000737:chemistry; D052878:Urolithiasis / Q000235:genetics*; D055815:Young Adult
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid; D003553:Cystine