What is Choroideremia?

Choroideremia (CHM) is a rare inherited retinal disorder that causes progressive vision loss and can ultimately lead to complete blindness. The disease affects the retina, the light-sensitive tissue at the back of the eye responsible for vision.

Cause of CHM

CHM is caused by changes in the CHM gene, which makes a protein called REP-1 (Rab escort protein-1). REP-1 helps small signal proteins attach to an enzyme that allows them to fit into the cell’s membrane, letting nutrients pass between cells. This process happens continuously in the retina, supplying the cells with nutrients needed to keep vision pathways functioning properly.

Another protein, REP-2, is present in all cells and can normally support cell function if REP-1 is missing. However, in the retina, REP-2 may not be enough to replace REP-1. In males with CHM, the defective REP-1 protein is quickly lost, and REP-2 cannot fully compensate. Because males have only one X chromosome, they have no backup copy of the CHM gene, so the retina cannot produce enough functional REP-1 protein.

One area of research supported by the Choroideremia Research Foundation (CRF) is finding ways to help retinal cells produce normal REP-1 protein.

Three men with choroideremia standing side by side and smiling; two of the men are using white canes.

Genetic Testing & Diagnosis

CHM shares many symptoms and exam findings with another retinal condition called retinitis pigmentosa (RP), so patients are often misdiagnosed. Genetic testing is the only way to confirm the cause of vision loss.

Testing may be available at no cost or covered by insurance. Identifying the correct genetic mutation is important because new therapies in development target specific mutations.

Imaging of retinitis Pigmentosa (RP) vs. Choroideremia (CHM) Later Stage.

In later stages of retinitis pigmentosa (RP), several retinal features differ from those seen in CHM. The optic nerve often appears much paler, with a “waxy” look (white arrows). Retinal blood vessels—particularly the arterioles—tend to be thinner (black arrows). Areas of dark pigment known as bone spicules are commonly observed (yellow arrows). In addition, cystoid macular edema (CME) occurs more frequently in RP.

Rarity of CHM

CHM is considered a rare disease, affecting an estimated 1 in 50,000-100,000 individuals.

Visual Changes in Choroideremia

As choroideremia progresses, the retina and underlying layers at the back of the eye develop characteristic patterns of degeneration. Early on, small areas of pigment change create a mottled, “salt-and-pepper” appearance. Over time, pigment is lost in the peripheral retina while the central macula remains intact, leading to tunnel vision. In advanced stages, widespread atrophy exposes the white sclera and deep blood vessels, resulting in a washed-out appearance and severe vision loss. The image below illustrates these stages of CHM progression in affected males.

Composite image showing the progression of choroideremia in a male across four stages. In the early stage, retinal pigment epithelial cells display hypo- and hyperpigmentation with a “salt-and-pepper” appearance; the pigment layer is more transparent, revealing choroidal blood vessels, corresponding to night blindness in childhood. In the mid stage, the pigment layer is absent in the periphery but preserved in the central macula, reflecting progressive narrowing of the visual field. In the late stage, widespread degeneration exposes the underlying white sclera with a “white-out” appearance and extensive choriocapillaris atrophy, associated with severe loss of visual acuity. In the end stage, typically by ages 60–70, the retina shows near-total pigment loss and advanced atrophy, corresponding to blindness.

Progression of choroideremia (CHM) in males: night blindness in early childhood, gradual narrowing of the visual field, significant loss of visual acuity in later stages, and eventual blindness in late adulthood (60–70 years).

Learn More

For a detailed comparison of choroideremia (CHM) and retinitis pigmentosa (RP), refer to our Clinical Differential Diagnosis PDF.

For a clear and informative overview of choroideremia, watch CHM 101 with Dr. Mariya Moosajee, where she explains the causes, symptoms, and current research in an easy-to-understand format: