Cystinosis is a condition in which the body accumulates the amino acid cystine (a building block of proteins) within cells. Excess cystine forms crystals that can build up and damage cells. These crystals negatively affect many systems in the body, especially the kidneys and eyes.
There are three distinct types of cystinosis. In order of decreasing severity, they are nephropathic cystinosis, intermediate cystinosis, and non-nephropathic or ocular cystinosis. Infants affected by nephropathic cystinosis initially exhibit poor growth and a particular type of kidney damage (renal Fanconi syndrome) that causes the kidneys to eliminate certain molecules that should be reabsorbed into the bloodstream. The kidney problems lead to the loss of important minerals, salts, fluids, and other nutrients. The loss of nutrients impairs growth and may result in soft, bowed bones (hypophosphatemic rickets), especially in the legs. The nutrient imbalances in the body lead to increased urination, thirst, dehydration, and abnormally acidic blood (acidosis). By about the age of 2, cystine crystals may be present in the clear covering of the eye (cornea). The buildup of these crystals in the eye causes an increased sensitivity to light (photophobia). Untreated children will experience complete kidney failure by about the age of 10. Other signs and symptoms that may occur in untreated people, especially after adolescence, include muscle deterioration, blindness, inability to swallow, diabetes, and thyroid and nervous system problems.
The signs and symptoms of intermediate cystinosis are the same as nephropathic cystinosis, but they occur at a later age. Intermediate cystinosis typically becomes apparent in affected individuals in adolescence. Malfunctioning kidneys and corneal crystals are the main initial features of this disorder. If intermediate cystinosis is left untreated, complete kidney failure will occur, but usually not until the late teens to mid-twenties.
People with non-nephropathic or ocular cystinosis usually do not experience growth impairment or kidney malfunction. In most cases, the only symptom is photophobia due to cystine crystals in the cornea.
Cystinosis affects approximately 1 in 100,000 to 200,000 newborns. The incidence is higher in the province of Brittany, France, where the disorder affects 1 in 26,000 individuals.
All three types of cystinosis are caused by mutations in the CTNS gene. Mutations in this gene lead to a deficiency of a transporter protein called cystinosin. Within cells, this protein normally moves cystine out of the lysosomes, which are compartments in the cell that digest and recycle materials. When cystinosin is defective or missing, cystine accumulates and crystallizes in the lysosomes. The buildup of cystine crystals damages cells in the kidneys and eyes and may also affect other organs.
Read more about the CTNS gene.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
These resources address the management of cystinosis and may include treatment providers.
You might also find information on treatment of cystinosis in
Educational resources and Patient support.
You may find the following resources about cystinosis helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
- Cystine storage disease
- Cystinoses
The resources on this site should not be used as a substitute for
professional medical care or advice. Users seeking information about
a personal genetic disease, syndrome, or condition should consult with a qualified
healthcare professional.
See How can I find a genetics professional in my area? in the Handbook.