A.Choroideremia is a rare, X-linked recessive genetic eye disease that causes blindness due to degeneration of the choroid, retinal epitheleum and the retina. Choroideremia, also called tapetochoroidal dystrophy, occurs almost exclusively in males. In childhood, night blindness is the most common first symptom. As the disease progresses, there is a steady loss of peripheral or side vision which eventually leads to total blindness. There is also evidence of loss of color perception and depth perception among Choroideremia patients. The rate of progression varies among individuals with Choroideremia, even among siblings.

A.Choroideremia is caused by a defect on the X gene. This defect prohibits the body from making RAB Escort Protein-1, or REP-1. This protein is essential for proper eye function. Without REP-1, the nutrients which keep the back layers of the eye functioning properly are not conveyed to that area. Degeneration of the eye results. Vision loss due to choroideremia is caused by degeneration of several layers of cells that are essential to sight. These layers, which line the inside of the back of the eye, are called the choroid, the retinal pigment epithelium and the retina. The choroid is a network of blood vessels located between the retina and the sclera, the "white of the eye." Choroidal vessels provide the retinal pigment epithelium and photoreceptor cells in the retina with oxygen and nutrients. The retinal pigment epithelium, directly beneath the retina, supports the function of photoreceptor cells. Photoreceptors are responsible for converting light into the electrical impulses that transfer messages to the brain where "seeing" actually occurs. In the early stages of choroideremia, the choroid and the retinal pigment epithelium initially deteriorate. Eventually, photoreceptor cells also degenerate. As a result, vision is lost.

A.The Choroideremia gene product is called REP-1 (for Rab escort protein-1). This protein functions to bring other small proteins (thinking of them as signals) into association with an enzyme that adds 20-carbon long chains to the small signals. These signal proteins can then fit into the lipid membrane that sorrounds the cell. The small signals are thought to play a role in allowing nutrients to pass across cells. Imagine that this process occurs constantly at the back of the eye as special nutrients are required to keep the biochemical pathways of vision operating at capacity while our eyes are open. Apparently there is another protein called REP-2 in all other cells except the eye that allows normal cell function IF REP-1 is not present. Unfortunately, the male patient with Choroideremia makes a defective REP-1 protein that is rapidly lost from the eye and REP-2 is not able to replace its function. You recall that the gene is on the X-chromosome. Males only have one X and so only one copy of the gene that makes the protein. If the gene copy is changed, there is no other normal copy around to mask the effect of not having the normal protein available. Research is trying hard to find ways of getting the cells in the eye to make the normal protein. Having an animal model of Choroideremia will be very important to test if the animal can be successfully treated before trying this in the human condition. (Special thanks to Dr. Ian MacDonald, University of Alberta, Canada, for this explanation)

A.Choroideremia is what is known as an X-linked recessive disease. Other more common diseases that you may know of that are X-linked recessive are Hemophilia and the "Boy In The Bubble" disease. What this means is that there is a defect in the encoding of the X-chromosome that results in a mutation, causing the disease. It is almost exclusively found in males, as females have 2 X genes, so if one is defective, the other "good" X can still do its job.

A.Women have 2 X genes. Men have 1 X and 1 Y gene. It takes the Y gene from a male and an X gene from the female to create a male. Conversely, it takes the X gene from the male and an X gene from the female to create a female. When a female is a carrier of Choroideremia, there is a 50/50 chance that her offspring will either have Choroideremia (male offspring) or be a carrier of Choroideremia (female offspring). The reason a female child will not get Choroideremia is that the male contributes a non-defective X gene, which properly produces the REP-1 protein. When a male has Choroideremia, it is a 100% certainty that any female offspring will be carriers of Choroideremia, as it takes the males defective X gene (combined with a female X gene) to create a female. Because the Y gene is needed from an affected male to create a male offspring (in conjuction with a female X), a male offspring of a male Choroideremia patient will not have the disease.

A.We maintain an extensive database on Choroideremia and other retinal degenerative diseases on our sister site, located at www.choroideremia.org There you can find information on Choroideremia and links to various organizations dedicated to ending blindness.

A.The Choroideremia Research Foundation, Inc. maintains a free online email support group through yahoogroups. You can join the group by going to our sister site at www.choroideremia.org and clicking on the link to subscribe to the listserve. Via email, you will receive support, encouragement, tips on dealing with Choroideremia in your life, information, and much needed humor. This listserve has become a lifeline for many people with Choroideremia. Being a rare disease, many people do not know anyone else with Choroideremia. As one member put it, "It's nice to know you're not alone".