Effects of cysteamine therapy in nephropathic cystinosis.

We studied the effects of cysteamine in five children with nephropathic cystinosis who were treated for up to 30 months. Cysteamine caused a decline in leukocyte cystine levels to the range seen in clinically unaffected heterozygotes; both plasma and urinary cystine diminished by more than half. Therapy had no effect on progressively declining creatinine clearance in three patients, but improvement occurred in the other two. Phosphaturia, glycosuria, aminociduria, and organic aciduria did not improve in any of the patients. Both blood lactate and the lactate pyruvate ratio were diminished. Growth velocity, which was abnormal in four of the five children, did not improve. No major side effects were noted. Therapy with cysteamine caused a consistent, dose-related decline in levels of cystine in leukocytes and in extracellular fluid, caused no improvement so far in renal tubular function or growth velocity, and improved creatinine clearance in some patients.