Ascorbic acid treatment in nephropathic cystinosis in identical twins.

Metabolic studies were performed on two HLA identical 9 1/2-year-old twins with nephropathic cystinosis during 14 months' participation in a double-blind study to evaluate ascorbic acid treatment for cystinosis. Replacement therapy was identical in both children throughout the study except for the use of ascorbic acid. Leukocyte cystine content was markedly abnormal and elevated in both children prior to, during, and after the ascorbic acid study. We postulate that the lack of improvement in growth or chemical parameters in the twin treated with ascorbic acid was due to the ineffectiveness of ascorbic acid in decreasing intracellular cystine content.