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Cystinosis

Cystine accumulates in body tissues

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Updated April 23, 2006

Cystinosis is an inherited disorder of chromosome 17 in which the amino acid cystine is not transported properly out of the body’s cells. This causes tissue and organ damage throughout the body. The symptoms of cystinosis may begin at any age, and it affects both males and females of all ethnic backgrounds. There are only around 2,000 known individuals with cystinosis in the world.

The gene for cystinosis (CTNS) is inherited in an autosomal recessive manner. This means that in order for a child to inherit the disorder, both parents must be carriers of the CTNS gene, and the child must inherit two copies of the defective gene, one from each parent.

Symptoms
The symptoms of cystinosis vary depending on which form of the disease is present. Symptoms may range from mild to severe, and they may progress over time.

  • Infantile nephropathic cystinosis –This is the most common and most severe form of cystinosis, in which symptoms begin in infancy, often before age 1 year. Children with this type of cystinosis often have short stature, changes in the retina (retinopathy), sensitivity to light (photophobia), vomiting, loss of appetite, and constipation. They also develop impaired kidney function known as Fanconi syndrome. Symptoms of Fanconi syndrome include excessive thirst (polydipsia), excessive urination (polyuria), and low blood potassium (hypokalemia).
  • Late-onset (also called intermediate, juvenile, or adolescent) nephropathic cystinosis – In this form, symptoms generally are not diagnosed before age 12 years, and the disease progresses slowly over time. Cystine crystals are present in the cornea and conjunctiva of the eye and in the bone marrow. Kidney function is impaired, and individuals with this form of cystinosis may also develop Fanconi syndrome.
  • Adult (benign or nonnephropathic) cystinosis – This form of cystinosis begins in adulthood and does not result in kidney impairment. Cystine crystals accumulate in the cornea and conjunctiva of the eye, and sensitivity to light (photophobia) is present.

Diagnosis
Diagnosis of cystinosis is confirmed by measuring the level of cystine in blood cells. Other blood tests can check for the imbalances in potassium and sodium, and the level of cystine in the urine can be checked. An ophthalmologist will examine the eyes for changes to the cornea and retina. A kidney tissue sample (biopsy) can be examined under a microscope for cystine crystals and for destructive changes to the kidney cells and structures

Treatment
The drug cysteamine (Cystagon) helps eliminate cystine from the body. Although it cannot reverse damage already done, it can help slow or prevent further damage from occurring. Cysteamine is very beneficial to individuals with cystinosis, especially when started early in life. Individuals with photophobia or other eye symptoms may apply cysteamine eye drops directly to the eyes.

Because of impaired kidney function, children and adolescents with cystinosis may take mineral supplements such as sodium, potassium, bicarbonate, or phosphate, as well as Vitamin D. If the kidney disease progresses over time, one or both kidneys may function poorly or not at all. In this case, a kidney transplant may be needed. The transplanted kidney is not affected by cystinosis. Most children and adolescents with cystinosis receive regular care from a pediatric nephrologist (kidney doctor).

Children who have difficulty growing may receive growth hormone treatments. Children with the infantile form of cystinosis may have difficulty with swallowing, vomiting, or abdominal pain. These children need to be evaluated by a gastroenterologist, and may require additional treatments or medications to control their symptoms.

Last updated 4/22/06

Sources:
- Elenberg, E. (2003). Cystinosis. eMedicine, accessed at http://www.emedicine.com/ped/topic538.htm
- National Organization for Rare Disorders. Cystinosis
- Medline Plus. (2005). Fanconi’s syndrome.

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