Adolescent cystinosis, presenting with proteinuria.

Isolated proteinuria preceding tubular dysfunction for years was the presenting laboratory sign in a patient with adolescent cystinosis, followed up to end-stage renal failure in the second decade of life. The renal biopsy showed the early characteristic features, multinucleated giant podocytes. The diagnosis was documented by slit lamp examination of the eyes and cystine determination in fibroblasts.