Cystinosis is a disorder of amino acid metabolism in which the amino acid cystine accumulates within the cell. Several forms exist, including the most common form with an onset during infancy, one with an onset during adolescence, and one with an adult onset.
The amino acid cystine accumulates within cells as crystals and impairs normal function of numerous organs, including the thyroid gland, the ovaries, pancreas, the cornea and especially the kidneys. Patients with onset during childhood have severe kidney disease leading to permanent damage and may require kidney transplants in the first to third decades of life. Damage to muscles and nerves also occurs and in severe, early onset forms, growth may be stunted. In the late onset, adult form, kidney damage does not occur.
The crystals can be directly visualized in the cornea in all three forms where they create irritation and light sensitivity. Sometimes the presence of the crystals causes a breakdown of the superficial tissue causing severe pain and tearing that is difficult to treat. Accumulation of crystals in the retina in the early onset forms eventually damages the light sensing cells reducing vision in the early onset forms.
This is an autosomal recessive disorder with a horizontal pattern of inheritance. Parents who carry the mutation and are clinically normal, have a 1 in 4 chance of having another affected child from each pregnancy.
The diagnosis in severe forms is often made by pediatricians from the presence of kidney disease. Ophthalmologists can detect the crystals by examination of the cornea. The administration of the drug cysteamine can dramatically improve kidney function and other symptoms especially if administered orally before the age of two years. It can also be administered to the eye in drops which reduces the number of crystals and results in a decrease in light sensitivity and irritation.