MAINTENANCE OF GOOD VISUAL ACUITY IN BEST DISEASE ASSOCIATED WITH CHRONIC BILATERAL SEROUS MACULAR DETACHMENT

Photoreceptor Function and Structure in Autosomal Dominant Vitelliform Macular Dystrophy Caused by BEST1 Mutations

Purpose

The purpose of this study was to evaluate rod and cone function and outer retinal structure within macular lesions, and surrounding extralesional areas of patients with autosomal dominant Best vitelliform macular dystrophy caused by BEST1 mutations.

Methods

Seventeen patients from seven families were examined with dark- and light-adapted chromatic perimetry and optical coherence tomography. Subsets of patients had long-term follow-up (14-22 years, n = 6) and dark-adaptation kinetics measured (n = 5).

Results

Within central lesions with large serous retinal detachments, rod sensitivity was severely reduced but visual acuity and cone sensitivity were relatively retained. In surrounding extralesional areas, there was a mild but detectable widening of the subretinal space in some patients and some retinal areas. Available evidence was consistent with subretinal widening causing slower dark-adaptation kinetics. Over long-term follow-up, some eyes showed formation of de novo satellite lesions at retinal locations that years previously demonstrated subretinal widening. A subclinical abnormality consisting of a retina-wide mild thickening of the outer nuclear layer was evident in many patients and thickening increased in the subset of patients with long-term follow-up.

Conclusions

Outcome measures for future clinical trials should include evaluations of rod sensitivity within central lesions and quantitative measures of outer retinal structure in normal-appearing regions surrounding the lesions.

The Clinical Features and Genetic Spectrum of a Large Cohort of Chinese Patients With Vitelliform Macular Dystrophies

PURPOSE

To provide the clinical and genetic characteristics of a large cohort of Chinese patients with vitelliform macular dystrophies.

DESIGN

Cross-sectional study.

METHODS

One hundred and thirty-four unrelated Chinese patients diagnosed with Best vitelliform macular dystrophy (BVMD), autosomal recessive bestrophinopathy (ARB), or adult vitelliform macular dystrophy (AVMD) were enrolled. Detailed ophthalmic examinations and genetic testing on vitelliform macular dystrophy-related genes were performed. Genotype and phenotype association were analyzed among different diagnostic groups.

RESULTS

In total, 87 BVMD, 30 AVMD, and 17 ARB patients were enrolled in this study. Genetic analysis identified 37 BEST1 mutations in 53 patients with BVMD and ARB. Of these, 5 variants (c.254A>C, c.291C>G, c.722C>G, c.848_850del, c.1740-2A>C) were novel. The variant c.898G>A was a hotspot mutation, which was identified in 13 patients with BVMD and 1 patient with ARB. There were significant differences of ocular biometric parameters among patients with homozygous or compound heterozygous mutations, heterozygous mutations, and those without mutations of BEST1. Homozygous or compound heterozygous patients had shortest axial length (AL), shallowest anterior chamber depth (ACD), and highest intraocular pressure (IOP); patients without mutations had longest AL, deepest ACD, and lowest IOP; and heterozygous patients were in between. Moreover, 7 patients harboring heterozygous mutations in BEST1 and 3 patients without BEST1 mutations showed similar clinical appearance to ARB in our cohort.

CONCLUSIONS

This is the largest sample size study of Chinese vitelliform macular dystrophy patients. Our results indicated that assessment of angle-closure risk is a necessary consideration for all types of BEST1-related vitelliform macular dystrophies. The study expanded both the clinical and genetic findings of 3 common types of vitelliform macular dystrophies in a Chinese population.

Multimodal Imaging in Best Vitelliform Macular Dystrophy

Purpose

In patients diagnosed with Best vitelliform macular dystrophy (BVMD), quantitative fundus autofluorescence (qAF), near-infrared fundus autofluorescence (NIR-AF), and spectral-domain optical coherence tomography (SD-OCT) were used to elucidate pathogenic mechanisms.

Methods

Fourteen patients heterozygous for BEST1 mutations were recruited. qAF was analyzed using short-wavelength fundus autofluorescence (SW-AF) images. Mean gray levels (GL) were determined in nonlesion areas (7 to 9° eccentricity) and adjusted by GL measured in an internal fluorescent reference. NIR-AF images (787 nm; sensitivity of 96) were captured and saved in non-normalized mode. Horizontal SD-OCT images also were acquired and BVMD was staged according to the OCT findings.

Results

In the pre-vitelliform stage, NIR-AF imaging revealed an area of reduced fluorescence, whereas in the vitelliruptive stage, puncta of elevated NIR-AF signal were present. In both SW-AF and NIR-AF images, the vitelliform lesion in the atrophic stage was marked by reduced signal. At all stages of BVMD, nonlesion qAF was within the 95% confidence intervals for healthy eyes. Similarly, the NIR-AF intensity measurements outside the vitelliform lesion were comparable to the healthy control eye. SD-OCT scans revealed a fluid-filled detachment between the ellipsoid zone and the hyperreflectivity band attributable to RPE/Bruch's membrane.

Conclusions

NIR-AF imaging can identify the pre-vitelliform stage of BVMD. Mutations in BEST1 are not associated with increased levels of SW-AF outside the vitelliform lesion. Elevated SW-AF within the fluid-filled lesion likely reflects the inability of RPE to phagocytose outer segments due to separation of RPE from photoreceptor cells, together with progressive photoreceptor cell impairment.

Mutant Best1 Expression and Impaired Phagocytosis in an iPSC Model of Autosomal Recessive Bestrophinopathy

Autosomal recessive bestrophinopathy (ARB) is caused by mutations in the gene BEST1 which encodes bestrophin 1 (Best1), an anion channel expressed in retinal pigment epithelial (RPE) cells. It has been hypothesized that ARB represents the human null phenotype for BEST1 and that this occurs due to nonsense mediated decay (NMD). To test this hypothesis, we generated induced pluripotent stem cells (iPSCs) from a patient with ARB and her parents. After differentiation to retinal pigment epithelial (iPSC-RPE) cells, both BEST1 mRNA and Best1 protein expression were compared to controls. BEST1 mRNA expression levels, determined by quantitative PCR, were similar in ARB iPSC-RPE, parental cells, and genetically unrelated controls. Western blotting revealed that CRALBP and RPE65 were expressed within the range delineated by unrelated controls in iPSC-RPE from the ARB donor and her parents. Best1 protein was detected in different clones of ARB iPSC-RPE, but at reduced levels compared to all controls. When tested for the ability to phagocytose photoreceptor outer segments, ARB iPSC-RPE exhibited impaired internalization. These data suggest that impaired phagocytosis is a trait common to the bestrophinopathies. Furthermore, ARB is not universally the result of NMD and ARB, in this patient, is not due to the absence of Best1.