Ethnic disparities in inherited retinal degenerations.

Objective: Inherited retinal degenerations (IRD) are clinically heterogeneous. There has been little study of the influence of ethnicity on IRD phenotypes. We aim to assess clinical and genetic variability between differing ethnic groups affected by IRD.

Design: Retrospective cohort study.

Participants: Patients with genetically resolved IRD (ABCA4, USH2A, RPGR) at a single centre (University of British Columbia).

Methods: Clinical and genetic data were contrasted between ethnic groups (Caucasian, East Asian, South Asian, Indigenous, African) and between Caucasians and non-Caucasians.

Results: 143 patients met the inclusion criteria. Caucasians were over-represented (76%). For ABCA4, East Asians most commonly had bullseye maculopathy, while classic Stargardt disease predominated in other ethnicities; cataract was less prevalent in non-Caucasians (p = 0.001). For USH2A, most non-Caucasians had non-syndromic IRD, while Caucasians were 50% isolated and 50% Usher syndrome. Hyperautofluorescent rings were more common in non-Caucasians (p = 0.027). In RPGR, best-corrected visual acuity was worse for Caucasians (logMAR 0.76 ± 0.69) than non-Caucasians (0.49 ± 0.30; p = 0.047), and myopia was greatest in South Asians (-9.56 ± 0.27 D vs -3.82 ± 4.05 D; p < 0.001). Twenty-one novel genetic variants were identified, and only 3.3% (5/154) of genetic variants were shared between ethnic groups.

Conclusions: Clinical and genetic differences are apparent between ethnic groups, even within "common" IRD genotypes. Awareness of these different retinal and extra-retinal (e.g., myopia, less favourable VA) features is critical to facilitate diagnostic accuracy and optimal clinical care, including access to novel therapies. Further work to expand the genetic reference databases for non-Caucasian ethnic groups is needed to facilitate equitable access to diagnosis and treatment for IRD.