ADOLESCENT CYSTINOSIS: COMPARISONS WITH INFANTILE AND ADULT FORMS

Abstract

Two adolescent siblings with a new form of cystinosis are distinctive because of their present age (15 and 14 years), their mild nephropathy, and the absence of retinopathy and pigmentary changes. The intracellular concentration of free cystine in their fibroblasts and leukocytes is 3 to 6 µmoles/gm protein, which is lower than in fatal infantile cystinosis and slightly higher than in the benign adult trait. The cystine is localized predominantly in the "granular" fraction. Both parents of the adolescent cystinotic siblings have excessive cystine retention in fibroblasts and leukocytes in the range which is typical of infantile cystinotic heterozygotes but cystine storage is not directly proportional to gene dosage. Dithiothreitol reduces the cystine content of "adolescent" fibroblasts, as it does in "infantile" cells. The three cystinotic traits indicate that several mutant alleles, at one or more gene loci, affect one or more gene products which control the steady-state of cystine metabolism in the cell. Clinical prognosis is apparently influenced to some extent by the severity of cystine retention.