Choroideremia (CHM) is a genetic eye disorder named because it primarily affects the choroid, a blood-rich cell layer that sits beneath the retina. Because of the interconnectedness of the choroid, the retinal pigment epithelium (RPE), and the photoreceptors of the retina, however, all three of these cell layers are affected.
The hallmark symptoms of choroderemia are the same as those of Retinitis Pigmentosa (RP)--night blindness and peripheral vision loss. Choroideremia causes progressive vision loss, and often results in legal blindness from loss of peripheral vision by the age of 40. As cone photoreceptor cells become more affected, central vision also begins to deteriorate.
Choroideremia is an X-linked trait caused by a mutation or deletion of the CMH gene. Because it is linked to the X chromosome, choroideremia primarily affects males. Rarely, women are affected, though usually to a lesser extent than the affected males in their family. Genetic testing is available to confirm the diagnosis and to identify female carriers at-risk of having affected sons.
Choroideremia is a very rare disease, affecting approximately 1 in 100,000 people.
Choroideremia is often confused with X-linked Retinitis Pigmentosa (RP), especially early in the course of the disease. A specialist in retinal degenerations can accurately distinguish between the two.