Nephropathic Cystinosis in Adults

Cystinosis is an autosomal recessive lysosomal storage disorder caused by a defect in the carrier-mediated system that normally transports cystine out of lysosomes. As a consequence, tissues accumulate variable amounts of the disulphide amino acid cystine. Three overlapping clinical phenotypes are recognized, varying in severity and age of onset. The most severe, the infantile nephropathic form (MIM 219800), appears in the first year of life. The late-onset form (MIM 219900) is also nephropathic, while ocular, non-nephropathic cystinosis manifests largely with corneal crystal deposition (MIM 219750). Infantile cystinosis is the most common form. Affected children develop renal proximal tubulopathy at 6 to 12 months of age. In the absence of treatment, renal failure occurs, with progression to end-stage renal disease (ESRD). Cystine crystal deposition in the cornea leads to photophobia and continuous widespread cystine accumulation eventually leads to rickets, retinal, endocrinological (hypothyroidism and impaired glucose tolerance), hepatic, gastrointestinal, muscular, and neurological abnormalities.