ChoroideremiaCHM) is a rare, X-linked recessive form of hereditary retinal degeneration that affects roughly 1 in 50,000 males. The disease causes a gradual loss of vision, starting with childhood night blindness, followed by peripheral vision loss, and progressing to loss of central vision later in life. Progression continues throughout the individual's life, but both the rate of change and the degree of visual loss are variable among those affected, even within the same family.
Choroideremia is caused by a mutation in the CHM gene which encodes Rab escort protein 1 (REP1), a protein involved in lipid modification of Rab proteins. While the complete mechanism of disease is not fully understood, the lack of a functional protein in the retina results in cell death and the gradual deterioration of the retinal pigment epithelium photoreceptors, and the choroid.
As of 2018, there is no treatment for choroideremia; however, retinal gene therapy clinical trials have demonstrated a possible treatment.
Choroideremia gene therapy
The choroideremia gene therapy involves a surgical, subretinal injection of healthy retina cells.
During the surgery, the fovea, the central portion of the macula where pinpoint central focusing vision is achieved, is deliberately detached by the surgeon’s sub-retinal fluid injection.
The therapeutic fluid that is injected contains healthy cells that are inserted into adeno-associated virus (AAV). The virus is designed to “infect” the damaged choroid and retinal tissue with the healthy therapeutic cells, thus rebuilding the damaged tissue.
Choroideremia is a genetic disorder that causes blindness in men. It affects approximately one in 50,000 people. The condition is caused by a fault in the gene known as CHM.
The CHM gene makes a protein called REP-1. It’s in every cell in the body and is a key player in how cells work, helping some of the machinery inside the cells get to the right place. When REP-1 is missing from the light-sensitive layer of the eye (the retina), this doesn’t happen. It gradually kills the retinal cells but we don’t yet understand exactly how.
A similar treatment to this is gene therapy for vision loss caused by RPE65-meidated inherited retinal dystrophy. The drug name is Luxterna
