Cystinosis

Abstract

Cystinosis is a rare autosomal recessive disease caused by mutations in the lysosomal cystine transporter cystinosin encoded by the CTNS gene (17p.13.2). Cystinosis is characterized by lysosomal cystine accumulation throughout the body with renal Fanconi syndrome being the most common presenting symptom of a multisystem disorder. It must be distinguished from cystinuria in which formation of cystine stones is the core problem. When left untreated, kidney dysfunction gradually progresses towards end-stage renal failure during the first 10 years of life. The advent of renal replacement therapy allowed cystinosis patients to survive into adulthood, but revealed numerous extrarenal manifestations of the disease, affecting eyes, endocrine organs, gastrointestinal tract, muscles, and central and peripheral nervous systems. The disease mechanism of cystinosis is not fully understood. The administration of the cystine-depleting agent cysteamine slows down renal and extrarenal organ damage, pointing to the pivotal role of cystine accumulation in the disease pathogenesis. Treatment with cysteamine should be initiated as early as possible and continued lifelong, and also after kidney transplantation for protecting extrarenal organs. Cysteamine eye drops are an indispensable part of the treatment of corneal cystine accumulation. Life expectancy of cystinosis patients has substantially improved and is now above 50 years.