Choroideremia is an inherited disease that causes progressive loss of vision due to degeneration of cell layers in the retina, the tissue that lines the back wall of the eye and makes vision possible. The affected layers include the choroid, the retinal pigment epithelium or RPE, and the photoreceptors. The choroid consists of blood vessel layers located between the retina and the sclera. Choroidal vessels provide the RPE and photoreceptors with oxygen and nutrients necessary for normal function. The RPE provides essential support functions for photoreceptors. The photoreceptors are responsible for converting light into the electrical impulses that are transferred to the brain where the images we see are created.
Living with Choroideremia
As an X-linked disease, choroideremia occurs primarily in males. In childhood, night blindness is the most common first symptom. As the disease progresses, there is loss of peripheral vision or “tunnel vision” and later a loss of central vision. Progression of the disease continues throughout the individual’s life, although both the rate and the degree of visual loss can vary, even within the same family.
Choroideremia is caused by mutations in the CHM gene. The condition is passed down in families by the X-linked pattern of inheritance. In this type of inheritance, the mutated gene for the disease is located on the X chromosome. Females have two X chromosomes and can carry the disease gene on one of their X chromosomes. Because they have a healthy version of the gene on their other X chromosome, carrier females are usually not affected by X-linked diseases. Males have only one X chromosome (paired with one Y chromosome) and are therefore genetically susceptible to X-linked diseases. Males with X-linked diseases pass their Y chromosome to their sons, and therefore will never pass an X-linked disease to their sons. Female carriers have a 50 percent chance (or 1 chance in 2) of passing the X-linked disease gene to their daughters, who become carriers, and a 50 percent chance of passing the gene to their sons, who are then affected by the disease.
Living with the Disease
There are many services and accommodative and assistive resources available to people and families with choroideremia. Visit the Foundation’s Living and Thriving pages to learn about many of these resources. A low vision specialist can help recommend the resources that are right for you.
More information on managing choroideremia is in the Newly Diagnosed section of this Web site.
Genetic testing is available for choroideremia. It helps with attaining an accurate diagnosis and assessing the risk of passing the disorder from parent to offspring. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.