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What is Cystinosis?
Cystinosis is a metabolic disease characterized by an abnormal accumulation of the amino acid cystine in various organs of the body such as the kidney, eye, muscle, pancreas, and brain. Different organs are affected at different ages.
Is it Inherited?
The disease is inherited in an autosomal recessive fashion, meaning that each parent of a child with cystinosis carries one defective gene and one normal gene. The parents never have any signs of the disease.
What Causes Cystinosis?
The cystine content of cystinotic cells averages 50-100 times the normal value. The cause is a defect in the transport of cystine out of a cell compartment called the lysososme, in which cystine accumulates. Because of cystine's low solubility, this amino acid forms crystals within the lysosomes of cells, and this is probably what destroys the cells.
What are the symptoms?
There are three clinical forms of cystinosis. Infantile (or nephropathic) cystinosis; late-onset cystinosis; and benign cystinosis. The latter form does not produce kidney damage. Infantile and late-onset cystinosis differ in the age of appearance of the first symptoms and in the rapidity of the clinical course. Infantile cystinosis is usually diagnosed between 6 and 18 months of age with symptoms of excessive thirst and urination, failure to thrive, rickets, and episodes of dehydration. These findings are caused by a disorder called renal tubular reabsorb nutrients and minerals. As a consequence, these important molecules are lost in the urine. Children with cystinosis also have crystals in their eyes (after one year of age) and an increased level of cystine in their white blood cells. Without specific treatment, children with cystinosis develop end-stage renal failure, i.e., lose their kidney function, at approximately 9 years of age.
If cystinosis patients receive a kidney transplant and reach adulthood, their new kidney will not be affected by the disease. However, without cysteamine treatment (see below), they can develop complications in other organs due to the continued accumulation of cystine throughout the body. These complications can include muscle wasting, difficulty swallowing, diabetes, hypothyroidism, and blindness. Not all older patients develop these problems, however.
Can Cystinosis Be Treated?
The symptomatic treatment of the Fanconi syndrome is essential. The urinary losses of water, salts, bicarbonate, and minerals must be replaced. Most children receive a solution of sodium and potassium citrate, as well as phosphate. Some also receive extra vitamin D.
The aim of specific treatment for cystinosis is to reduce cystine accumulation within the cells. This goal is achieved by cysteamine treatment, which has proven effective in delaying or preventing renal failure. Cysteamine also improves growth of cystinosis children. The Food and Drug Administration (FDA) has approved a capsule form of cysteamine called CYSTAGON, to be taken every 6 hours each day. Recently Raptor Pharmaceuticals received FDA approval of a delayed release cysteamine therapy, name Procysbi. Patients take Procysbi twice a day.
Kidney transplantation has proven very helpful in patients with cystinosis, and cysteamine therapy should be considered to try to prevent the late complications of the disease (see above).
Both young children with cystinosis and older patients with a kidney transplant, cysteamine eyedrops, marketed by Sigma-Tau Pharmaceuticals under the name Cystaran, are available for the treatment of corneal cystine crystals. Cystaran treatment has been available by prescription in the United States since 2013, when it was approved by the Food and Drug Administration.
Is Prenatal Detection Available?
Today, prenatal diagnosis is available for families known to be at risk for having a child with cystinosis. Chorionic villus sampling is performed at 8-9 weeks of gestation; amniocentesis can be performed at 14-16 weeks of gestation.
What are Possible Future Developments?
Much remains to be learned about cystinosis. Investigators are trying to identify the abnormal gene which causes this condition.
Other investigators are trying to determine the best therapies for each complication. Some questions which remain include:
Information provided by William A. Gahl, M.D., Ph.D.,
National Institutes of Health,
Disclaimer: The information presented above is intended for general education purposes only, and should not be construed as advising or diagnosis or treatment of this or any other medicla condition.