Disease expression caused by different variants in the BEST1 gene: genotype and phenotype findings in bestrophinopathies

Abstract

Purpose: To analyse the spectrum of clinical features and molecular genetic data in a series of patients carrying likely disease-associated variants in the BEST1 gene.

Methods: Retrospective observational analysis of clinical data extracted from the medical records of visual function, multimodal imaging and electrophysiology of 62 eyes of 31 patients. Molecular genetic analysis was performed by means of panel-based NGS or Sanger sequencing.

Results: The spectrum of variants in the BEST1 gene comprised 19 different variants and three of which are novel. Fundus photographs and OCT images allowed categorization of 52 eyes as Best vitelliform macular dystrophy (BVMD) with stages 1 to 5 and 10 eyes with autosomal recessive bestrophinopathy (ARB), with more severe phenotype. One patient was shown to be heterozygous for a variant, which has so far been described only in ARB, but this patient had the BVMD phenotype. There was no significant progression of the visual acuity during the follow-up period of 5 years both in BVMD and ARB. The most prevalent pattern of fundus autofluorescence (FAF) in BVMD was 'patchy'. There were diverse visual field defects in static automated perimetry (SAP) depending on the stage. The Arden ratio was significantly lower in ARB patients and in eyes with stage 5 of BVMD.

Conclusions: The genotype does not always predict the phenotype in patients with BVMD and ARB; however, having two mutations in the BEST1 gene causes a more severe phenotype. FAF helped to distinguish ARB from BVMD. Most of the observed eyes did not progress functionally during the follow-up. ARB and the atrophic stage of BVMD as the disease end-stage had the worst visual functions and EOG results.

Keywords: autosomal dominant bestrophinopathy; best vitelliform macular dystrophy; genotype; phenotype.