Cystinosis is a rare metabolic disease that causes deposits of cystine in various organs. This is caused by a defect in the transport of cystine. In general, three types of cystinosis are distinguished: the infantile, juvenile and ocular form. The infantile form is the most common one, the first symptoms appear at the age of three months. These include a delayed body weight gain, polyuria polydipsia syndrome and Toni-Debré-Fanconi syndrome.

A progressive accumulation of cystine in other organs results in symptoms such as hypothyroidism, diabetes mellitus, hepatosplenomegaly, and additionally cerebral and muscular symptoms. If there are also deposits in the eyes, the flow of the lungs and photophobia may appear. The progression of the disease leads to a renal failure at the age of about 6 years.

The juvenile form occurs at the approximal age of eight and follows a similar course, leading to renal failure at approximately the age of 15 years. The ocular form usually occurs in adults. Those affected suffer from photophobia, but have otherwise no symptoms. As a cause, mutations or deletions in the CTNS gene could be detected for all three forms. The disease is autosomal recessive. The affected gene is responsible for the synthesis of cystinosin.