Choroideremia

Choroideremia is a rare X-linked recessive inherited retinal disease affecting 1 in every 50,000-100,000 individuals.¹ The mutated gene, the CHM gene in Choroideremia, is passed more commonly to males versus females through the X chromosome through the X chromosome of a unaffected carrier mother.^1,2 Choroideremia affects both the photosensitive layers of the retina, but also the pigmented layers, included the retinal pigmented epithelium (RPE) and the choroid.¹ In Choroideremia, RPE degeneration is characterized by “scalloping” of this pigmented area, as well as, pigment clumping of the retina occurs.³ 

Signs and symptoms of Choroideremia are more severe in males and more mild in female carriers, but in females, signs and symptoms can be more varied.³ 

• Nyctalopia (night blindness) [1st decade] 
• Loss of peripheral vision [1st decade]^1,3 
• Rapid decrease in central vision [later in life, usually 5th-7th decade]^3,4  
• Color vision deficiencies [later in life, usually 5th-7th decade]⁴  

Choroideremia is a genetic condition and is inherited via an X-linked recessive manner to males from their carrier mother. It is caused by a mutation in the CHM gene, which causes issues with the retina, including the retinal pigmented epithelium (RPE) and choroid (pigmented layer behind the retina).^1,2 

Ophthalmic examination with dilated fundus examination (DFE): an eye care practitioner can measure visual acuity and note characteristics of Choroideremia by viewing the retina in the back of the eye. 

Fluorescein angiography (FA): fluorescein dye is injected intravenously into the patient’s arm allowing the dye to travel to retinal blood vessels, displaying blood flow, as well as, if any blood vessels are leaking. 

Ocular coherence tomography (OCT): ultrasound scan of the retinal layers, which may display thinning and later, cysts, in patients with Choroideremia. 

OCT angiography (OCTA): similar to an OCT, ultrasound scan of retinal layers, but including retinal and choroidal blood vessel visualization.⁴

Electroretinogram (ERG): measures the function of the retina based on responses to flashes, which can detect retinal disease prior to changes in appearance of the retina.⁵ 

Fundus auto-fluorescence (FAF): non-invasive retinal imaging that can detect retinal dystrophies and diseases early on.⁶

Visual field testing, commonly Humphrey Visual Field (HVF): clicker test that maps out a patient’s visual field, which can appear constricted and patchy in patients with Choroideremia, depending on disease severity and progression. 

Genetic testing: available for the mutations that causes Choroideremia.⁴

There is no current FDA-approved treatment for Choroideremia, but gene therapy with viral vectors for this condition is currently being investigated by the FDA.^3,4 

Choroideremia is a progressive retinal disease that causes slow deterioration of vision. Eye examinations as recommended by a patients’ eye care provider is important to assess changes to retinal appearance, constriction of visual field, and effect on visual acuity. Complications associated with Choroideremia include cataracts, macular edema, and choroidal neovascularization, further emphasizing the importance of recommended eye exams with a doctor.³ Low vision evaluations are recommended to established devices that can assist with visual function and improve quality of life. Some of these devices include filters on lenses, magnifiers, large print materials, and so much more. Counseling and support groups for patients with Choroideremia or other inherited retinal diseases (IRDs) are an excellent option for career and life support.  

1. Mitsios, A., Dubis, A. M., & Moosajee, M. (2018). Choroideremia: from genetic and clinical phenotyping to gene therapy and future treatments. Therapeutic Advances in Ophthalmology, 10. https://doi.org/10.1177/2515841418817490 
2. Basta, M., & Pandya, A. M. (2021, May 8). Genetics, X-Linked Inheritance. PubMed.Gov. Retrieved January 13, 2022, from https://pubmed.ncbi.nlm.nih.gov/32491315/ 
3. Pennesi, M. E., Birch, D. G., Duncan, J. L., Bennett, J., & Girach, A. (2019). CHOROIDEREMIA. Retina, 39(11), 2059–2069. https://doi.org/10.1097/iae.0000000000002553 
4. Tripathy, K., ND, Sousa, D. C., Bracha, P., MD, Weldy, E., MD, Cole, E. D., MD, Hyde, R. A., MD, PhD, Lim, J. I., MD, & Karth, P. A., MD. (2021, June 7). Choroideremia. EyeWiki. Retrieved January 13, 2022, from https://eyewiki.aao.org/Choroideremia 
5. Harden, A., Adams, G. G., & Taylor, D. S. (1989). The electroretinogram. Archives of disease in childhood, 64(7), 1080–1087. https://doi.org/10.1136/adc.64.7.1080  
6. Yung, M., Klufas, M. A., & Sarraf, D. (2016). Clinical applications of fundus autofluorescence in retinal disease. International Journal of Retina and Vitreous, 2. https://doi.org/10.1186/s40942-016-0035-x