Contributor: Gordon K. Klintworth
Childhood cystinosis (cystinosin defect, lysosomal cystine transport protein defect, nephropathic cystinosis, OMIM #219800) is one variety of cystinosis. It is a rare autosomal recessive inherited lysosomal storage disease caused by a mutation in the CTNS gene, which encodes for cystinosin. Cystine crystals accumulate within cells in bone marrow, liver, spleen, lymph nodes, and kidneys. because of a defect in a lysosomal cystine transport protein. Tinsel-like, fine white crystals appear in the subepithelial conjunctival tissue. The crystals are insoluble in absolute ethanol, but soluble in many other solutions. Plasma cystine and cysteine levels are not consistently elevated. A tissue biopsy of affected tissue can establish the diagnosis. Other conditions that are associated with corneal crystals need to be distinuished from cystinosis. It is the most severe form of cystinosis. A ~65 kb deletion is present in most patients suggesting that most cases have an ancient common ancestor. Nephropathic cystinosis is associated with defective renal tubular reabsorption and the renal Fanconi syndrome. Renal failure is common. A biopsy of affected tissue can establish the diagnosis. Nephropathic cystinosis is the most common inherited cause of proximal tubular dysfunction (renal Fanconi syndrome). Cystine continues to accumulate in different organs after renal transplantation.