Definition:
Cystinosis is a very rare metabolic, genetic disorder that causes a particular amino acid known as cystine to accumulate in the body’s organs. The accumulation occurs because a lysosomal membrane protein, called cystinosin, whose function is to transport the amino acid, cystine, out of the lysosome, is defective.  The inability of cystinosin to function properly renders cystine unable to be transported out of the lysosome, where it instead accumulates.

Cystine is marked by low solubility which means that it does not dissolve well into another substance. Given its low solubility, cystine forms crystals within the lysosome. It is believed that these crystals destroy cells and give rise to the symptoms of this disorder.

The mutated gene in Cystinosis has been identified. Molecular diagnosis and carrier testing is now possible.

There are three forms of Cystinosis: Infantile, juvenile, and adult. Infantile is the most severe of the three forms. The adult form of the disorder is considered benign.

Cystinosis affects approximately one in every 100,000 to 200,000 live births.  In the province of Brittany, France, the incidence is much higher affecting one in every 26,000 individuals.  In the United States, approximately 300-400 children are afflicted with Cystinosis.

Symptoms:
In the infantile form of Cystinosis, symptoms begin to appear around 10 months of age, when the affected child’s growth measures far behind the standards for this age bracket. Frequent urination, constant thirst, and irritability are common features of the disorder during this time. By one year of age, an affected child cannot walk and can only bear a small amount of his or her body weight with caution.  Corneal crystals appear during this time. The affected child may develop rickets and suffer episodes of dehydration. During the affected individual’s 20s to 30s, swallowing difficulties and muscle complications arise.

In the juvenile form, symptoms appear between eight and 12 years of age and are marked by kidney and visual complications.

The primary complication associated with Cystinosis is the failure of the kidneys to absorb nutrients and minerals. These substances, lost in the urine, must be replaced. This condition, also called renal tubular Fanconi Syndrome, is marked by a craving for salty food, picky eating habits, and by slow physical growth. If this condition is left untreated, an affected child can develop kidney failure by 10 years of age.

In the adult form, cystine develops in the corneas but kidney function is not affected.

Inheritance Pattern:
Cystinosis is an autosomal recessive disorder.

Life Expectancy:
Life expectancy for the infantile and juvenile forms of Cystinosis is during the affected individual’s 20s to 30s.

Diagnosis and Testing:
Cystinosis is diagnosed by measuring the levels of cystine in blood or tissue samples. If these levels are elevated in comparison to standard cystine values, a diagnosis can be made. Additionally, slit-lamp examination of the eyes to look for cystine crystals can be performed as early as one year of age. Prenatal testing is also available for known carriers.

Treatment:
In the past, treatment for Cystinosis was limited to replacing the loss of substances in the urine, but with the advent of the drug Cysteamine and kidney transplants, the management and prognosis of this disorder has greatly improved.

The FDA-approved drug Cysteamine (Cystagon) is the standard treatment for this disorder. This drug lowers the levels of cystine in the cells and effectively prevents or delays renal failure. The drug also improves the growth of children afflicted with Cystinosis.

Other therapies are focused on treating such symptoms of this disorder as an inability of the kidneys to absorb nutrients and minerals. Ensuring that the child consumes fluids that contain electrolytes is imperative to prevent kidney failure. Phosphates, a type of electrolyte, and vitamin D are routinely given to patients, to increase the uptake of phosphate by the kidneys and to prevent rickets.

Kidney transplants have been effective for individuals affected by Cystinosis, but patients are encouraged to take Cystagon to prevent further complications. Cysteamine eyedrops remove the cystine crystals that accumulate in the corneas.

Patient Groups:
Cystinosis Foundation
604 Vernon Street
Oakland, CA 94610
www.cystinosisfoundation.org
tel: (800) 392-8458
fax: (559) 222-7997
Jean Hotz, President
Email@cystinosis.com

Cystinosis Research Foundation
18802 Bardeen Avenue
Irvine, CA 92612
www.natalieswish.org
tel: (949) 223-7610
fax: (949) 756-5955
Nancy Stack
HEYSTACK4@aol.com

Cystinosis Research Network
302 Whytegate Court
Lake Forest, IL 60045
www.cystinosis.org
tel: (866) 276-3669
fax: (847) 235-2773
Christy Greeley
Greeleycd@aol.com