Choroideremia – February, 2024
History:
A 14-year-old male presented at the request of his mother who was a carrier for an inherited condition. While he denied any visual complaints, his mother preferred for him to be evaluated. He had no difficulty at school or playing sports and denied any issues with night vision.
Exam:
Visual acuity was 20/20 in both eyes (OU) without glasses and IOP was normal. Anterior segment exam was unremarkable. Dilated fundus exam revealed peripheral pigment mottling with focal areas of atrophy OU (Fig 1 and 2). OCT showed outer retinal atrophy and thin choroid OU (Fig 3 and 4). It was revealed that his maternal grandfather had a diagnosis of Choroideremia. Genetic testing was performed which confirmed this genotype.
Differential Diagnosis:
• Gyrate atrophy
• Ocular albinism
• Retinitis pigmentosa
• Choroideremia
Discussion:
Choroideremia
Choroideremia is an X-linked recessive condition with mutations in the CHM gene, which predominantly affects males. This chorioretinal dystrophy results in diffuse degeneration of the photoreceptors, RPE, and choriocapllaris. It has an estimated prevalence of 1 in 50,000.
Symptoms often begin in the first to second decade of life with poor night vision and peripheral visual loss. Central vision is usually preserved until age 50-70 when the fovea becomes involved.
Fundus examination progresses from widespread pigment clumping to well-defined regions of atrophy with visible underlying sclera and large choroidal vessels. This progresses in a centripetal manner with a small island of foveal tissue which remains preserved until much later at which point color vision and central vision become affected. ERG shows reduced scotopic function early in life before photopic component also becomes affected.
Some patients may also develop macular edema, choroidal neovascularization, and posterior subcapsular cataracts. Currently, there is no commercially available treatment for choroideremia, however gene therapy using viral vectors is currently being investigated with some promising results.
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References:
- MacDonald IM, Sereda C, McTaggart K, et al. Choroideremia gene testing Expert Rev Mol Diagn 2004;4: 478-484. PMID: 15225095
- MacDonald IM, Hume S, Chan S, Seabra MC. Choroideremia. In: Pagon RA, Adam MP, Ardinger HH, et al., eds. GeneReviews(R). Seattle (WA): University of Washington, Seattle University of Washington, Seattle. All rights reserved.; 1993.
- Edwards TL, Jolly JK, Groppe M, et al. Visual Acuity after Retinal Gene Therapy for Choroideremia. The New England journal of medicine. 2016;374(20):1996-1998.