The job of the CTNS gene is to make cystinosin. Cystinosin transports, or carries, the amino acid cystine out of the lysosomesLysosomes are the organelles within the cells in your body that act as cell digestive system. Lysosomes break apart amino acids such as cystine.

If you or your child has cystinosis, either your body does not make cystinosin, or the cystinosin that your body makes does not work well. As a result, cystine builds up inside lysosomes. Over time, the cystine forms into crystals.

Cystine crystals may build up in cells in every organ of your body, including your eyes. The corneathe front layer of the eye is the part of the eye that may be affected the most. In the cornea, these crystals are usually pointed and needle-shaped, and look like shards of glass. Cystine crystals may also build up in your conjunctiva, retina, and iris.

The cornea has very important functions:

• It bends light entering your eye to help your eye focus
• It protects against infection and damage to inner parts of your eye