NORD gratefully acknowledges Lisa Vawter, PhD, Medical Writer, Ian M. MacDonald, MD, CM, Professor, Department of Ophthalmology and Visual Sciences, University of Alberta, and Stephanie Chan, MSc, Genetic Counsellor, Department of Ophthalmology and Visual Sciences University of Alberta, Royal Alexandra Hospital, for assistance in the preparation of this report.
Choroideremia is characterized by extensive loss of all retinal layers in the eyes. This disorder usually begins during childhood with wasting (atrophy) of the pigmented retinal epithelium, retina, and choroid. The retina is the light sensitive, most internal layer, consisting of many nerve containing layers. A layer of single pigmented cells is the layer outside of the retina. The choroid is the next layer located between the retina and the “white” section of the eye (the sclera); this layer contains small blood vessel).
Degeneration of the blood vessels of the choroid is followed by damage to the retina, which usually leads to loss of peripheral vision that can progress to eventual blindness. Central vision is usually preserved until late in life. The symptoms of choroideremia may vary greatly between affected individuals. Female carriers usually have very mild symptoms with night blindness or sensitivity to glare occurring late in life.
Choroideremia can be caused by many different mutations in the CHM gene. The CHM gene encodes REP1 (RAB escort protein 1), a protein that takes part in targeting vesicles (small sacs of substances) into, out of, and within cells.
Choroideremia is an X linked recessive genetic condition. These disorders are caused by an abnormal gene on the X chromosome and manifest mostly in males. Females who have an altered gene on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms, because females have two X chromosomes and only one carries the altered gene. Males have one X chromosome that is inherited from their mothers; if a male inherits an X chromosome that contains the altered gene, he will develop the disease.
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.
If a male with an X linked disorder has a child, he will pass the altered gene to all of his daughters, who will be carriers. A male cannot pass an X linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring.
Choroideremia affects primarily males. Female carriers generally have few or no symptoms. However, a small number of females develop 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 number of people have been diagnosed with choroideremia; approximately one in forty persons.
A doctor will perform tests that examine the patient’s visual field suspected of having choroideremia and will look inside the eye for degeneration of the retina. Genetic testing is available for some genetic variants that cause choroideremia.
The symptoms of choroideremia can be treated but the disease itself cannot yet be cured. Organizations providing services to sight impaired people help patients and their families. Genetic counseling is recommended for families affected by this disorder.
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For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
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