Autosomal Recessive Bestrophinopathy (ARB): A Clinical and Molecular Description of Two Patients at Childhood

Background: Autosomal recessive bestrophinopathy (ARB) is associated with mutations in BEST1. ARB is rarely diagnosed compared to BEST1-associated autosomal dominant (a.d.) juvenile vitelliform macular degeneration (Morbus Best, VMD). This is not only due to its low prevalence, but also to the phenotypic appearance. This paper describes typical features in two patients and discusses novel findings using improved ophthalmological diagnostic tools. Material and Methods: Two unrelated boys with reduced visual acuity as well as five further relatives underwent a comprehensive ophthalmological examination including electroretinography (ERG) and electrooculography (EOG) according to ISCEV standard, fundus autofluorescence (FAF) and spectral-domain optic coherence tomography (SD-OCT). BEST1 was screened for mutations based on the clinical diagnosis. Results: Visual acuity ranged between 0.2 and 0.5 in the patients. Multifocal yellowish paramacular and peripheral lesions were visible in the fundus correlating with spots of increased FAF. The lesions correlated with thickening of the RPE layer. Especially in the inner nuclear layer hyporeflective areas were visible, reminiscent of retinoschisis but without changes of FAF. In both patients the ganzfeld ERG was within the normal range and the mfERG presented obvious reductions of amplitudes in the central area. The EOG did not show a light peak. Goldmann perimetry was normal for isopters III/4e and I/4e. The fundus controlled perimetry revealed a central sensitivity loss. Molecular genetic analysis identified four (two novel) mutations in BEST?, in the compound heterozygous state in both patients. The screened relatives carried one of the mutations in the heterozygous state and were ophthalmologically unremarkable apart from age-related changes. Conclusion: ARB is a rare disease, presenting with obvious differences to a.d. Mobus Best. The phenotype can easily be identified by the extramacular multifocal yellowish lesions with increased FAF and accompanied by early loss of visual acuity. Specific diagnostic tests like OCT, FAF recordings and electrophysiology support the diagnosis. Molecular genetic screening confirms the diagnosis and the autosomal recessive inheritance.