Choroideremia is caused by the deletion of the Rab escort protein 1 (REP1). Rab escort protein 2 (REP2) is 75% identical and can almost compensate for the loss of REP1. The REPs are essential for the prenylation of Rab proteins. Studies have shown that there is a build up of unprenylated Rab27 in lymphoblasts from Choroideremia patients.
Generally, only men show symptoms of this disease, although in rare cases some women also acquire it. Initially a person suffering from choroideremia has night blindness, which begins in youth. As the disease progresses, a CHM sufferer loses their peripheral vision and depth perception, eventually losing all sight by middle age. In some cases, a severe loss of acuity and color perception become evident as the disease progresses.
The link between the loss of REP1 and the build up of unprenylated Rab27 and the degeneration of the eye is unknown as yet.
At this time, there is no treatment or cure for this disease.
- Griscelli syndrome. Type two Griscelli syndrome is caused by the loss of Rab27. It has completely different symptoms from Choroideremia