Best Vitelliform Macular Dystrophy Natural History Study Report 1: Clinical Features and Genetic Findings.

PURPOSE:To analyze the genetic findings, clinical spectrum and natural history of Best vitelliform macular dystrophy (BVMD) in a cohort of 222 children and adults. DESIGN:Single-center retrospective, consecutive, observational study. PARTICIPANTS:Patients with a clinical diagnosis of BVMD, from pedigrees with a likely disease-causing monoallelic sequence variant in the BEST1 gene. METHODS:Data were extracted from electronic and physical case notes. Electrophysiologic assessment and molecular genetic testing were analyzed. MAIN OUTCOME MEASUREMENTS:Molecular genetic testing, clinical findings including best-corrected visual acuity (BCVA), choroidal neovascularization (CNV) rates, and electrophysiology parameters. RESULTS:222 patients (127 males and 95 females) from 141 families were identified, harboring 69 BEST1 variants, including 22 novel variants. Mean age at presentation was 26.8 years (range 1.3-84.8 years) and most patients (61.5%) presented with a deterioration of central vision. Major funduscopic findings at presentation included: 128 eyes (30.6%) with yellow vitelliform lesions, 78 eyes (18.7%) with atrophic changes, 49 eyes (11.7%) with fibrotic changes, 48 eyes (11.5%) with mild pigmentary changes and 43 eyes (10.3%) showing a vitelliruptive appearance. Mean BCVA was 0.37 LogMAR (20/47) for the right eye and 0.33 LogMAR (20/43) for the left eye at presentation, with a mean annual loss rate of 0.013 LogMAR and 0.009 LogMAR respectively over a mean follow-up of 9.6 years. 37 patients (17.3%) were diagnosed with CNV over a mean follow-up period of 8.0 years (range 0-55 years). Eyes with CNV that received treatment with anti-VEGF had a better mean VA compared to eyes that were not treated with anti-VEGF (0.28 LogMAR (20/38) versus 0.62 LogMAR (20/83). The majority of eyes exhibited a hyperopic refractive error (185/235, 78.7%) and 13 patients (6.1%) were diagnosed with amblyopia. Among the three most common variants, p.A243V was associated with a later age of onset, a better age-adjusted VA and less advanced Gass stages compared to p.R218C and p.R218H. CONCLUSIONS:BVMD shows a wide spectrum of phenotypic variability. The disease is very slowly progressive, and the observed phenotype-genotype correlations allow for more accurate prognostication and counselling.