Choroideremia is characterized by extensive loss of all retinal layers in the eye. This disorder usually begins during childhood with wasting (atrophy) of the pigmented retinal epithelium, retina, and choroid of the eye. The retina is the light-sensitive, most internal surface of the eyeball consisting of many, nerve-containing layers. A layer of single pigmented cells is next outside the retina. The choroid is the next vascular layer (membrane) located outside the retina and inside the “white” section of the eye (sclera). The choroid contains many small branches of vessels called the choriocapillaries.
Degeneration of the vessels of the choroid and functional damage to the retina occur later in life and usually lead to progressive peripheral visual field loss and eventual blindness. The symptoms of Choroideremia may vary greatly between affected individuals. Female carriers usually have very mild symptoms without vision loss.
Choroideremia is an X-linked recessive genetic condition. X-linked recessive disorders are caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one is ‘turned off’ and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not show symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is ‘turned off’. Males have one X chromosome and if they inherit an X chromosome that contains a disease gene, they will develop the disease. Males with X-linked disorders pass the disease to all of their daughters, who will be carriers. Males can not pass the X-linked gene to their sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
In 1991, Dr. Frans Cremers of the University of Nijmegen in the Netherlands isolated the gene responsible for Choroideremia. The gene makes a protein call Rab escort protein 1. This discovery may lead to a prenatal test and to treatment for the disease.
Choroideremia affects males. Female carriers are generally asymptomatic. However, a small number of females have developed the disorder as a result of a genetic process that inactivates the normal gene and leaves only the dysfunctional gene active. In the Salla area of northern Finland, an unusually high concentration of cases has occurred, affecting approximately one in forty persons.
Treatment of Choroideremia is symptomatic and supportive. Organizations providing services to sight-impaired people will be of help to patients and their families. Genetic counseling is recommended for families affected by this disorder.
Studies of families with Choroideremia are underway to determine the gene changes (mutations) responsible for the disorder. There is no common mutation that is found in all cases of choroideremia.
This disease entry is based upon medical information available through March 2000. Since NORD’s resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
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For information about clinical trials sponsored by private sources, contact:
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FROM THE INTERNET
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