Cystinosis is a genetic condition that causes the accumulation of the amino acid "cystine" in the cells of the body. Excessive amounts of cystine can damage cells, and form crystals that build up and damage various organs and tissues, including the kidneys, eyes, liver, thyroid, muscles, pancreas, brain and white blood cells. Depending on the type, cystinosis that is not treated can result in kidney failure.
Cause of Cystinosis
Cystinosis is a recessive genetic disease. If both parents carry the cystinosis gene, there is a 25 percent chance of their having a child with cystinosis.
Types of Cystinosis
There are three types of cystinosis, two of which, if left untreated, can lead to kidney failure.
Nephropathic cystinosis is the most severe form of the disease. Its symptoms develop in infancy, and include growth problems, and a kidney disorder known as Fanconi Syndrome, which prevents the kidneys from reabsorbing nutrients and minerals. This loss of nutrients impairs growth and can cause rickets. Dehydration and excessive thirst are also common symptoms. Cystine crystals may build up in the corneas of the eyes, causing eye pain and an increased sensitivity to light. It can also cause muscle problems, blindness, infertility, and thyroid and nervous system problems. Left untreated, nephropathic cystinosis can cause complete kidney failure by the age of 10.
Symptoms of intermediate cystinosis are the same as those of nephropathic cystinosis, but they begin in adolescence. Kidney problems, and eye pain and sensitivity are its main symptoms. Kidney failure can occur, but usually not until the late teens to early twenties.
Non-Nephropathic (Ocular) Cystinosis
The most common symptom of non-nephropathic (ocular) cystinosis is a crystal buildup in the corneas of the eyes, which causes pain and increased sensitivity to light (photosensitivity). Those with non-nephropathic cystinosis usually do not develop kidney problems or any of the other symptoms associated with cystinosis.
Most forms of cystinosis are diagnosed in childhood or infancy, although non-nephropathic cystinosis may be diagnosed at a later age because of its lack of severe symptoms.
Diagnosis of Cystinosis
Cystinosis may be suspected when children experience developmental delays and fail to grow at a normal rate, in addition to having other symptoms. To diagnose cystinosis, a physical examination is performed, and diagnostic tests, which include the following, ordered:
- Blood tests
- Ultrasound or MRI scan of the kidney
Blood and urine testing is done to check cystine levels. A kidney biopsy may also be performed to determine the cause of symptoms, and rule out any other conditions.
Treatment of Cystinosis
There is no cure for cystinosis; treatment focuses on managing symptoms and reducing cystine accumulation. "Cysteamine," a cystine-depleting drug that lowers cystine levels within cells, is a medication that is prescribed to prevent or delay kidney failure. Phosphates and vitamin D may be given to treat or prevent rickets. Corneal cystine-crystal accumulation can be treated with an ophthalmic solution called "Cystaran." People suffering from kidney dysfunction must stay hydrated, and can benefit from a high intake of fluids and electrolytes to prevent excessive loss of water. In severe cases, a patient with cystinosis may benefit from a kidney transplant.