Laterality of symptomatic cystine calculi.

Objectives: To evaluate patterns of laterality in cystine stone formation to determine whether phenotypic expression of this genetic disease is distributed equally in each kidney. Cystinuria is a genetic defect that may result in the formation of recurrent cystine calculi. Significant nongenetic factors may play a role in the manifestation of this disease.

Methods: Thirty-four patients seen in the Stone Center at the University of California, San Francisco were retrospectively evaluated for treatments and patterns of symptomatic stone formation between 1989 and 2002. A conservative surgical regimen and routine radiographic examinations were used. Treatments were used as a surrogate for development of symptomatic calculi.

Results: The mean age at last follow-up was 38.2 years. The mean age at presentation was 18 years. The 34 patients underwent a total of 249 procedures, averaging 7.3 procedures per patient. Of the 34 patients, 29% required only unilateral surgery and formed unilateral symptomatic calculi exclusively (P <0.0001) during their lifetime. Of the 10 patients with unilateral stone formation, 2 (20%) were female and 8 (80%) were male. Of the 24 patients with bilateral stone formation, 12 (50%) were female and 12 (50%) were male. Of the 10 patients with unilateral stone formation, 6 developed left-sided calculi and 4 developed right-sided calculi.

Conclusions: A subset of one third of patients with cystine stone formation will develop unilateral calculi exclusively during their lifetime. Understanding why the contralateral side did not form stones may provide insight into novel prophylactic regimens. The etiology of symptomatic unilateral cystine nephrolithiasis is unknown, but anatomic and external triggers should be considered.