Best Vitelliform Macular Dystrophy MCQ — NEET PG Practice Question | NEETPGAI
Best Vitelliform Macular Dystrophy
medium
eye Ophthalmology
A 12-year-old boy presents to the retina clinic with a complaint of gradual blurring of vision over the past 6 months. Fundoscopy reveals a well-demarcated, round, elevated yellow-orange subretinal deposit centered on the fovea, measuring approximately 1 disc diameter. The structure marked **B** in the diagram shows this classic "egg yolk" appearance. His best-corrected visual acuity is 20/30 in both eyes. An electro-oculogram (EOG) shows an Arden ratio of 1.2 (normal >1.8), while a full-field electroretinogram (ERG) is normal. Which of the following genetic mutations would most likely explain this patient's findings?
A. Mutation in PROM1 gene causing cone-rod dystrophy with early photoreceptor loss
B. Mutation in ABCA4 gene causing Stargardt disease with central flecks and beaten bronze macula
C. Mutation in PRPH2 gene causing adult-onset foveomacular vitelliform dystrophy with normal EOG
D. Mutation in BEST1 gene encoding bestrophin-1, a calcium-activated chloride channel in the RPE basolateral membrane
Explanation
Why "Mutation in BEST1 gene encoding bestrophin-1, a calcium-activated chloride channel in the RPE basolateral membrane" is right
Best vitelliform macular dystrophy (BVMD) is caused by autosomal dominant mutations in the BEST1 gene on chromosome 11q13, which encodes bestrophin-1. This protein is a calcium-activated chloride channel located in the basolateral membrane of the retinal pigment epithelium (RPE). Dysfunction of this channel impairs fluid and ion transport across the RPE, leading to accumulation of lipofuscin-like material between the RPE and photoreceptors. The clinical presentation in this case—the classic "egg yolk" vitelliform lesion (Stage 2), preserved vision (20/30), severely reduced EOG Arden ratio (1.2), and normal full-field ERG—is pathognomonic for BVMD. The abnormal EOG despite a normal fundus in early disease reflects the global RPE dysfunction caused by bestrophin-1 deficiency. (AAO BCSC Section 12; Boon et al, Prog Retin Eye Res 2009)
Why each distractor is wrong
Mutation in PRPH2 gene causing adult-onset foveomacular vitelliform dystrophy with normal EOG: Adult-onset foveomacular vitelliform dystrophy (AOFVD) presents later in life (typically >50 years), has a smaller lesion, and critically, shows a NORMAL EOG Arden ratio. This patient is 12 years old with a severely reduced EOG, making AOFVD unlikely.
Mutation in ABCA4 gene causing Stargardt disease with central flecks and beaten bronze macula: Stargardt disease (structure marked A) presents with central flecks and a beaten bronze or "dark choroid" macula, not a vitelliform lesion. The EOG is normal in Stargardt disease, unlike this patient's severely reduced ratio.
Mutation in PROM1 gene causing cone-rod dystrophy with early photoreceptor loss: PROM1 mutations cause cone-rod dystrophy with early photoreceptor dysfunction and abnormal full-field ERG. This patient has a normal ERG, ruling out a primary photoreceptor dystrophy.
High-YieldNEET PG
BVMD is the only macular dystrophy with a severely reduced EOG Arden ratio (<1.5) even in preclinical stages, because bestrophin-1 dysfunction affects the entire RPE, not just the macula. The normal ERG distinguishes it from generalized photoreceptor diseases.
AAO BCSC Section 12 — Retina and Vitreous; Boon et al, Prog Retin Eye Res 2009
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