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CHM gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

CHM gene

The CHM gene provides instructions for producing the Rab escort protein-1, which is critical for intracellular trafficking and the health of retinal cells.

Normal Function

The CHM gene provides instructions for producing the Rab escort protein-1 (REP-1), which is active throughout the body. REP-1 attaches (binds) to Rab proteins and directs them to the membrane of cell compartments (organelles). While attached to the membrane, the Rab protein plays a role in directing the movement of proteins and organelles within cells, a process known as intracellular trafficking. After the Rab protein reaches its destination, it is released by REP-1, which then attaches to another Rab protein to repeat the process.

Health Conditions Related to Genetic Changes

Choroideremia

More than 140 mutations in the CHM gene have been found to cause choroideremia. Nearly all of these mutations lead to the production of an abnormally small, nonfunctional REP-1 protein, or abolish its production entirely. A lack of normal REP-1 disrupts the ability of Rab proteins to aid in intracellular trafficking, causing cells to die prematurely.

While a similar protein, REP-2, can perform escort duties in many body tissues, very little REP-2 is present in the light-sensitive tissue at the back of the eye (the retina). Consequently, it cannot compensate for the loss of REP-1 in this tissue. The resulting misplacement of Rab proteins within retinal cells leads to the progressive vision loss characteristic of choroideremia.

Genomic Location

The CHM gene is found on the X chromosome.

Frequently Asked Questions

The CHM gene encodes the REP-1 protein, which handles intracellular trafficking via Rab prenylation. A related protein called REP-2 performs the identical function in most body tissues, effectively substituting for the missing REP-1 and preventing systemic organ damage. However, the retina and choroid produce negligible levels of REP-2. Because ocular tissues lack an adequate supply of this backup protein, Rab proteins cannot properly regulate membrane transport in retinal cells, resulting in tissue-specific cell death.
Patients should undergo annual evaluations with a retinal specialist, including visual field testing, optical coherence tomography (OCT), and fundus autofluorescence to track retinal degeneration. While gene therapy clinical trials are ongoing, current management focuses on preserving remaining vision: wearing 100% UV-protective sunglasses to reduce photo-oxidative retinal damage, avoiding tobacco use, utilizing low-vision rehabilitation aids, and accessing early genetic counseling for family planning.
Choroideremia is inherited in an X-linked recessive pattern caused by mutations on the CHM gene on the X chromosome. Males have only one X chromosome, so a single mutated copy causes progressive vision loss. Females carry two X chromosomes; while the majority of female carriers are asymptomatic or show only faint retinal pigmentary changes on examination, some can experience mild to moderate night blindness or patchy visual field loss due to skewed X-chromosome inactivation (lyonization), where the healthy copy is randomly turned off in a significant proportion of retinal cells.
The earliest symptom is typically night blindness (nyctalopia), which often begins in childhood or early adolescence. Vision loss then progresses to peripheral visual field constriction ("tunnel vision") during young adulthood as the choroid and retinal pigment epithelium degenerate from the periphery inward. Central visual acuity and color vision usually remain well-preserved until later in life, often persisting into the fifth or sixth decade before macular involvement occurs.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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