Novel Missense Mutations in BEST1 Are Associated with Bestrophinopathies in Lebanese Patients

ABCA4-related retinopathies in Lebanon

Variants in ATP-binding cassette transporter type A4 (ABCA4) have been linked to several forms of inherited retinal diseases (IRDs) besides the classically defined Stargardt disease (STGD), known collectively as ABCA4 retinopathies. ABCA4 is a sizable locus harboring 50 exons; thus, its analysis has revealed over 2,400 variants described, of which more than 2,000 are causal. Due to the clinical and genetic heterogeneity, diagnosing ABCA4 retinopathies is challenging. To date, no ABCA4-related retinopathy has been detected in Lebanon. Using next-generation sequencing, we analyzed our IRDs' cohort retrospectively (61 families) and identified five with ABCA4-related retinopathies, making it a relatively abundant cause of IRDs (about 8 %). Three families were diagnosed with rod-cone dystrophy (RCD), two with STGD, and one with cone-rod dystrophy (CRD). In conclusion, our study showed the presence of ABCA4 variants with a high degree of heterogeneity in Lebanon.

Paradoxical autosomal recessive bestrophinopathy-like phenotypes shown in an autosomal dominant pedigree

PURPOSE

This study aimed to evaluate the clinical and genetic characteristics of eight members from a Chinese Han family who displayed autosomal recessive bestrophinopathy (ARB)-like retinal changes in autosomal dominant (AD) inheritance pattern.

METHODS

Clinical investigations included slit-lamp, tonometry, fundus photography, spectral-domain optical coherence tomography, fundus autofluorescence, electrooculography, and ultrasound biomicroscopy. Ocular axial length measurements were collected retrospectively. The targeted exome sequencing (TES) was applied for the genetic analysis of the proband. PCR-based Sanger sequencing was performed on the family for validation and co-segregation analysis.

RESULTS

Eight members in the three-generation pedigree complained about vision loss and seven of them had detailed clinical assessments, demonstrating ocular phenotypes including extramacular and vascular arcades subretinal deposits and Arden ratio decline on electrooculography that resembled ARB. Bilateral anterior chamber structure abnormalities were observed in seven cases and three patients were diagnosed with angle-closure glaucoma. Despite clinical phenotypes supporting ARB, there was only a single heterozygous mutation of c.227T > C (p.Ile76Thr) in the BEST1 gene detected in all eight patients, which showcased AD inheritance.

CONCLUSIONS

An ARB-like phenotype could be caused by a heterozygous mutation of the BEST1 gene and inherited in an AD fashion.

The genetic landscape of inherited retinal dystrophies in Arabs

Inherited retinal dystrophies (IRDs) are a major cause of vision loss. Altogether are highly heterogeneous genotypically and phenotypically, exhibiting substantial differences worldwide. To shed more light on these conditions, we investigated the genetic and phenotypic landscape of IRDs in the Arabs globally and per country.We analyzed 1,621 affected individuals from 16 Arabic countries reported in 198 articles. At the phenotypic level, rod-cone dystrophy (RCD) and Usher syndrome were the most prevalent conditions among non-syndromic and syndromic IRDs. At the gene level, TULP1, ABCA4, RP1, CRB1, MYO7A, RPE65, KCNV2, and IMPG2 were the most mutated genes. Interestingly, all except CRB1 were highly prevalent because they harbored founder mutations, implying that consanguinity is a major determinant in Arab countries. Of note, ~ 93% of the investigated individuals carried homozygous mutations. The country analysis for the IRDs conditions and their associated genotypes revealed that whereas Leber Congenital Amaurosis, RCD, and USHER syndrome were widely distributed, bestrophinopathies and non-syndromic hearing loss were restricted to specific countries (till now).This study could be a starting point for initiating suitable health policies towards IRDs in the Arab world. The high degree of homozygosity urges the need for genetic counsellors to provide personalized information and support the affected individuals.

Genetic and clinical features of BEST1-associated retinopathy based on 59 Chinese families and database comparisons

Variants in BEST1 are one of the most common cause of retinopathy mainly involving the retinal pigment epithelium with both dominant and recessive traits. This study aimed to describe the characteristics of potential pathogenic variants (PPVs) in BEST1 and their associated clinical features. Variants in BEST1 were collected from our in-house exome sequencing data and systematically evaluated by in silico prediction tools as well as genotype-phenotype analysis. The pathogenicity features of the BEST1 variants were further assessed through database comparison among the in-house data, Genome Aggregation Database from the general population, and all previously published literature. The clinical information of the in-house patients was summarized. The PPVs in BEST1 were identified in 66 patients from 59 families, including 32 families with Best vitelliform macular dystrophy (BVMD) and 27 families with autosomal recessive bestrophinopathy (ARB). These PPVs included 31 missense variants, seven truncation variants, one in-frame deletion, and a known 3-untranslated region variant. All the truncations detected in our study were exclusively involved in ARB but not BVMD. Among the 31 missense variants, 18 missenses associated with BVMD in the dominant trait were clustered in four hotspot regions with statistically significant differences from the recessive missenses. Except for distinct macular changes, there were no statistically significant differences among the other associated clinical features between BVMD and ARB, including peripheral retinopathy, high hyperopia, and angle-closure glaucoma. In conclusion, BEST1-associated dominant retinopathy was preferentially caused by missense variants located in important functional regions. Truncations were most likely benign in heterozygous status. Future studies are expected to elucidate the mystery of the same missense variants contributing to both BVMD and ARB.

Novel BEST1 mutations and clinical characteristics of autosomal recessive bestrophinopathy in a Spanish patient

PURPOSE

To describe the clinical and genetic characteristics (novel mutation in BEST1 gene) of a Spanish patient with autosomal recessive bestrophinopathy (ARB).

METHODS

The detailed ophthalmological examination included best corrected visual acuity (BCVA), color and autofluorescence photography, fluorescein angiography, optical coherence tomography, and electrophysiology tests. A next-generation sequencing (NGS) strategy was applied to the index patient, and then sequenced in an Illumina NextSeq500 system.

RESULTS

A 55-year-old male presented with a BCVA of 20/25 in the right eye and 20/20 in the left eye. Fundoscopy revealed perifoveal yellow flecked-like lesions. Fluorescein angiography and fundus autofluorescence results were consistent with pattern dystrophy. A homozygous frameshift mutation in BEST1 (c.341_342del; p.(Leu114Glnfs*57)) was identified as the cause of the disease.

CONCLUSION

ARB is a genetic disease that leads to irreversible visual loss. In this report we found a novel mutation responsible for this disease.

Clinical Heterogeneity in Autosomal Recessive Bestrophinopathy with Biallelic Mutations in the BEST1 Gene

Autosomal recessive bestrophinopathy (ARB) has been reported as clinically heterogeneous. Eighteen patients (mean age: 22.5 years; 15 unrelated families) underwent ophthalmological examination, fundus photography, fundus autofluorescence, and optical coherence tomography (OCT). Molecular genetic testing of the BEST1 gene was conducted by the chain-terminating dideoxynucleotide Sanger methodology. Onset of symptoms (3 to 50 years of age) and best-corrected visual acuity (0.02–1.0) were highly variable. Ophthalmoscopic and retinal imaging defined five phenotypes. Phenotype I presented with single or confluent yellow lesions at the posterior pole and midperiphery, serous retinal detachment, and intraretinal cystoid spaces. In phenotype II fleck-like lesions were smaller and extended to the far periphery. Phenotype III showed a widespread continuous lesion with sharp peripheral demarcation. Single (phenotype IV) or multifocal (phenotype V) vitelliform macular dystrophy-like lesions were observed as well. Phenotypes varied within families and in two eyes of one patient. In addition, OCT detected hyperreflective foci (13/36 eyes) and choroidal excavation (11/36). Biallelic mutations were identified in each patient, six of which have not been reported so far [c.454C>T/p.(Pro152Ser), c.620T>A/p.(Leu207His), c.287_298del/p.(Gln96_Asn99del), c.199_200del/p.(Leu67Valfs*164), c.524del/p.(Ser175Thrfs*19), c.590_615del/p.(Leu197Profs*26)]. BEST1-associated ARB presents with a variable age of onset and clinical findings, that can be categorized in 5 clinical phenotypes. Hyperreflective foci and choroidal excavation frequently develop as secondary manifestations.

Next Generation Sequencing Identifies Five Novel Mutations in Lebanese Patients with Bardet-Biedl and Usher Syndromes

AIM

To identify disease-causing mutations in four Lebanese families: three families with Bardet-Biedl and one family with Usher syndrome (BBS and USH respectively), using next generation sequencing (NGS).

METHODS

We applied targeted NGS in two families and whole exome sequencing (WES) in two other families. Pathogenicity of candidate mutations was evaluated according to frequency, conservation, in silico prediction tools, segregation with disease, and compatibility with inheritance pattern. The presence of pathogenic variants was confirmed via Sanger sequencing followed by segregation analysis.

RESULTS

Most likely disease-causing mutations were identified in all included patients. In BBS patients, we found (M1): c.2258A > T, p. (Glu753Val) in BBS9, (M2): c.68T > C; p. (Leu23Pro) in ARL6, (M3): c.265_266delTT; p. (Leu89Valfs*11) and (M4): c.880T > G; p. (Tyr294Asp) in BBS12. A previously known variant (M5): c.551A > G; p. (Asp184Ser) was also detected in BBS5. In the USH patient, we found (M6): c.188A > C, p. (Tyr63Ser) in CLRN1. M2, M3, M4, and M6 were novel. All of the candidate mutations were shown to be likely disease-causing through our bioinformatic analysis. They also segregated with the corresponding phenotype in available family members.

CONCLUSION

This study expanded the mutational spectrum and showed the genetic diversity of BBS and USH. It also spotlighted the efficiency of NGS techniques in revealing mutations underlying clinically and genetically heterogeneous disorders.