Autosomal Recessive Bestrophinopathy: Clinical and Genetic Characteristics of Twenty-Four Cases

Multimodal imaging and genetic characteristics of autosomal recessive bestrophinopathy

PURPOSE

To report the ocular manifestations, multimodal imaging characteristics and genetic testing results of six patients with autosomal recessive bestrophinopathy (ARB).

METHODS

This was an observational case series including 12 eyes of 6 patients who were diagnosed with ARB. All patients underwent a complete ophthalmic examination including refraction, slit-lamp biomicroscopy, dilated fundus examination, fundus autofluorescence, optical coherence tomography and electrooculography. BEST1 gene sequencing was also performed for all patients.

RESULTS

The mean age was 22.8years and the male-female ratio was 0.50. All ARB patients had a hyperopic refractive error. A spectrum of fundus abnormalities, including multifocal yellowish subretinal deposits in the posterior pole, subfoveal accumulation of vitelliform material and cystoid macular edema, was observed. Fundus autofluorescence imaging demonstrated marked hyperautofluorescence corresponding to the yellowish subretinal deposits. Optical coherence tomography revealed serous retinal detachment, intraretinal cysts, brush border appearance caused by elongation of the outer segments of photoreceptors, and hyperreflective dome-shaped deposits at the level of the retinal pigment epithelium. Fundus fluorescein angiography showed hyperfluorescence with staining of the yellowish subretinal deposits. Electrooculography showed reduced Arden ratio in all patients. In addition, biallelic pathogenic variants in the BEST1 gene were detected in all patients.

CONCLUSION

ARB is a rare autosomal recessive inherited retinal disorder with biallelic pathogenic variants in the BEST1 gene and may present with a wide range of ocular abnormalities that may not be easily diagnosed. Multimodal retinal imaging in conjunction with EOG is helpful to establish the correct diagnosis.

Very Large Cystoid Macular Lesions Identified Using Outlier Analysis of Genetically Confirmed Inherited Retinal Disease Cases

BACKGROUND

Cystoid macular lesions (CML) in inherited retinal diseases (IRDs) can contribute to vision impairment. Studying the morphologic range and outlier presentations of CML may inform clinical associations, mechanistic research, and trial design. Thus, we aim to describe the distribution of optical coherence tomography (OCT) parameters in IRD cases with CML and identify phenotype-genotype associations in very large cystoid macular lesions (VLCML).

MATERIALS AND METHODS

This cross-sectional study retrieved clinical information from electronic records from January 2020 to December 2021. VLCML cases were identified using the robust distance (Mahalanobis) of the correlation between central foveal thickness (CFT) and total macular volume (TMV) and a 99.9% probability ellipse. The distribution of OCT parameters was calculated by genotype and phenotype.

RESULTS

We included 173 eyes of 103 subjects. The median age was 55.9 (interquartile range [IQR], 37.9, 63.7) and 47.6% (49/103) were females. Patients had disease-causing mutations in 30 genes. The most common genes included USH2A (n = 18), RP1 (n = 12), and ABCA4 (n = 11). Robust distance analysis showed that the prevalence of VLCML was 1.94% (n = 2 patients, 4 eyes). VLCML was seen in cases of NR2E3 (119-2A>C) and BEST1 (1120_1121insG) mutations. The median CFT in cases without VLCML was 269 µm (IQR 209, 318.50) while the median for VLCML cases was 1,490 µm (IQR 1,445.50, 1,548.00) (P < .001).

CONCLUSIONS

Subjects with different IRD genotypes may develop VLCMLs. Future studies could consider the range and outlier values of CML foveal thickness when determining inclusion criteria and biostatistical plans for observational and interventional studies.

Gene therapy in bestrophinopathies: Insights from preclinical studies in preparation for clinical trials

The BEST1 gene encodes bestrophin-1, a homopentameric ion channel expressed in the retinal pigment epithelium (RPE), where it localizes to the basolateral plasma membrane. Pathogenic variants in this gene can cause different autosomal dominant and recessive inherited retinal diseases (IRDs), collectively named "bestrophinopathies." These disorders share a number of clinical and molecular features that make them an appealing target for gene therapy. Clinically, bestrophinopathies are often slowly progressive with a wide window of opportunity, and the presence of subretinal material (vitelliform deposits and/or fluid) as a hallmark of these conditions provides an easily quantifiable endpoint in view of future clinical trials. From a molecular standpoint, most BEST1 pathogenic variants have been shown to cause either loss of function (LOF) of the protein or a dominant-negative (DN) effect, with a smaller subset causing a toxic gain of function (GOF). Both LOF and DN mutations may be amenable to gene augmentation alone. On the other hand, individuals harboring GOF variants would require a combination of gene silencing and gene augmentation, which has been shown to be effective in RPE cells derived from patients with Best disease. In this article, we review the current knowledge of BEST1-related IRDs and we discuss how their molecular and clinical features are being used to design novel and promising therapeutic strategies.

Autosomal recessive bestrophinopathy combined with neurofibromatosis type 1 in a patient

BACKGROUND

Neurofibromatosis type 1 (NF1) is a multisystem genetic disorder that may affect multiple systems of the body. Autosomal recessive bestrophinopathy (ARB) is a rare retinal dystrophy caused by autosomal recessively mutations in bestrophin 1 (BEST1) gene. So far, we have not retrieved any case report of the same patient with both NF1 and BEST1 gene mutations.

CASE PRESENTATION

An 8-year-old female patient with café-au-lait spots, freckling on skin presented to our ophthalmology clinic for routine ophthalmological examination. Her best corrected visual acuity (BCVA) was 20/20 in both eyes. Slit-lamp examination of both eyes revealed few yellowish-brown dome-shaped Lisch nodules over the iris surface. Fundus examination was notable for bilateral confluent yellowish subretinal deposits at macula, few yellow flecks at temporal retina, and cup-to-disc ratio of 0.2. Optical coherence tomography (OCT) revealed subretinal fluid (SRF) involving the fovea, elongated photoreceptor outer segments and mild intraretinal fluid (IRF) at bilateral macula. Fundus autofluorescence demonstrated hyperautofluorescence in the area corresponding to the subretinal deposits. Whole-exome sequencing and Sanger sequencing were used to investigate genetic mutation in the patient and her parents. A BEST1 gene heterozygous missense c.604 C > T (p.Arg202Trp) was identified in the patient and her mother. Also, the patient carries an NF1 nonsense mutation c.6637 C > T (p.Gln2213*) with the mosaic generalized phenotype. There were no visual impairments or obvious neurological, musculoskeletal, behavioral or other symptoms in this patient, so she was managed conservatively and advised to follow up regularly for a long time.

CONCLUSIONS

ARB and NF1, which are caused by two different pathogenic gene mutations, have rarely coexisted in the same patient. The discovery of pathogenic gene mutations may play a crucial role in more accurate diagnostics and genetic consultations for individuals and their families.

Case report: Autosomal recessive bestrophinopathy with macular cysts and MNV over 13-year follow-up

Purpose: To describe the phenotype and genotype of a patient with autosomal recessive bestrophinopathy (ARB) over a 13-year follow-up period.

Methods: The phenotype of the subject was described after a complete ophthalmological examination, which included fundus photography, optical coherence tomography (OCT), fundus autofluorescence, fluorescein angiography (FA), indocyanine green angiography (ICGA), electroretinogram (EOG), electroretinography (ERG), and multifocal electroretinogram (mfERG). Genetic analyses were carried out by screening the variations via whole-exome sequencing.

Results: This patient presented with retinoschisis and cystic changes when he was 7 years old and was diagnosed with X-linked retinoschisis. In the 13th year after the first presentation, enlarged macular cysts with retinoschisis, macular neovascularization (MNV), and subretinal fluid were displayed on OCT. Autofluorescence showed hyperfluorescence corresponding to the area of retinal pigment epithelium (RPE) change. EOG showed no light peak, and the Arden ratio was less than 2.0. Whole-exome sequencing revealed compound heterozygous sequence variations (p. [Arg47Leu; Trp287*]) in the coding sequence of the BEST1 allele inherited from his parents. Thus, a diagnosis of ARB combined with secondary MNV was made.

Conclusion: Patients with compound heterozygous BEST1 mutations developed ARB, which could show significant retinoschisis at a young age. Genetic analyses, autofluorescence, and EOG are essential to diagnose ARB correctly in consequence of considerable phenotypic variations.