Improved renal function in children with cystinosis treated with cysteamine.

BACKGROUND: The lysosomal storage disease cystinosis results in renal failure at approximately 10 years of age. Although oral cysteamine therapy is recognized to preserve kidney function, the extent of renal benefit has not been determined.
METHODS: Between 1960 and 1992, we determined 24-hour creatinine clearances in 76 children with cystinosis during 1081 admissions to the National Institutes of Health. Seventeen children were considered to have received adequate treatment with cysteamine, since they had depletion of cystine from leukocytes and began therapy before the age of 2 years; treatment lasted a mean of 7.1 years. Thirty-two children were considered to have received partial treatment, since they had poor compliance with therapy or began treatment after the age of 2; treatment lasted a mean of 4.5 years. Twenty-seven children were followed in the era before cysteamine therapy and thus never received cysteamine.
RESULTS: Of the 27 children who never received cysteamine, 16 were followed at the National Institutes of Health until renal failure occurred; their mean (+/- SD) creatinine clearance was 8.0 +/- 4.8 ml per minute per 1.73 m2 of body-surface area at a mean age of 8.3 +/- 1.9 years. Of the 17 children who received adequate treatment, none had renal failure; their mean creatinine clearance was 57 +/- 20 ml per minute per 1.73 m2 at 8.3 +/- 3.8 years of age. The mean creatinine clearance of the children who received partial or adequate treatment with cysteamine increased with age up to the age of five years and then declined linearly with age at a normal rate. For the children who received adequate treatment, the mean creatinine clearance was predicted to reach 0 ml per minute per 1.73 m2 at the age of 74 years, as compared with 20 years of age for the children who received partial treatment. With no therapy, the mean creatinine clearance reaches 0 ml per minute per 1.73 m2 at 10 years of age.
CONCLUSIONS: Children with cystinosis who are treated early and adequately with cysteamine have renal function that increases during the first five years of life and then declines at a normal rate. Patients with poorer compliance and those who are treated at an older age do less well.