Cystinosis and Mitochondrial Metabolism

Cystinosis is a monogenic autosomal recessive lysosomal storage disease with complete penetrance, caused by a biallelic mutation in the CTNS gene (17p13.2) encoding cystinosin, a ubiquitous membrane protein whose role is to clear cystine into the cytosol. Its dysfunction in patients with cystinosis leads to systemic accumulation of cystine, an oxidised dimer of cysteines linked by a disulphide bridge, in the lysosomal space, and irreversible cellular dysfunction. Renal damage is at the forefront, with Fanconi syndrome (proximal tubulopathy) and chronic renal failure developing early in childhood/adolescence. There are also multi-systemic disorders, notably endocrine and ophthalmological. Cysteamine is an amino thiol which reduces the level of intra-lysosomal cystine by breaking the disulphide strands of cystine, giving two cysteines which complex with cysteamine to leave the lysosome. Si