Ocular non-nephropathic cystinosis, also known as adult-onset cystinosis, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of the cysteine metabolism pathway. It is caused by a defect in the CTNS gene, which encodes the protein cystinosin, which acts as a cystine/H+ symporter that transports L-cysteine out of the lysosome. Ocular non-nephropathic cystinosis is characterized by a buildup of cysteine in cells, in the case of this form in the cornea. Symptoms include photophobia and damage to the cornea due to crystals forming from the excess cysteine. However, unlike other forms of cystinosis, no or minimal kidney damage occurs. Treatment with cysteamine, a drug that can convert cysteine into a form that can be secreted by the lysosome, can be effective in all of the forms of cystinosis. It is estimated that ocular non-nephropathic cystinosis affects less than 1 in 100,000 to 200,000 individuals, which is the rate of the more severe nephropathic cystinosis.

Cystinosis, Ocular Nonnephropathic References

Cysteine Metabolism References