Rhodopsin gene mutation analysis in Iranian patients with autosomal dominant retinitis pigmentosa

Mutation analysis of RHO in patients with non-syndromic retinitis pigmentosa

PURPOSE

To identify RHO mutations in patients with non-syndromic retinitis pigmentosa (NS-RP).

METHODS

A total of 143 probands (46 family history and 97 sporadic cases) with NS-RP were recruited from Southeast China. The coding exons and adjacent intronic regions of RHO were PCR-amplified and sequenced by Sanger sequencing. The candidate variant was evaluated by the guidelines of American College of Medical Genetics and further validated through co-segregation analysis within the family.

RESULTS

Five heterozygous mutations in RHO were detected in 5 out of 143 probands, where the frequency of RHO mutations in our cohort was approximately 3.5% (5/143) and 10.8% (5/46) for probands and families with NS-RP, respectively. Three known disease-causing mutations including c.C1030T (p.Q344X), c.C173G (p.T58R), and c.G266A (p.G89D) were identified in three unrelated families. The other two previously unreported mutations c.557C>A (p.S186X) and c.944delA (p.N315TfsX43) were confirmed in Family RP-087 and Family RP-139, respectively. These mutations co-segregated with available affected individuals in each family were not observed in the unaffected family members or in the 112 unrelated controls.

CONCLUSIONS

This report expands the mutational spectrum of RHO gene associated with NS-RP and demonstrates the frequency of RP RHO mutations in Southeast Chinese populations.

Genotypes and clinical features of RHO-associated retinitis pigmentosa in a Japanese population

PURPOSE

To report the genotypes and clinical features of RHO-associated retinitis pigmentosa (RHO-RP) in the Kyushu region of Japan.

STUDY DESIGN

Retrospective, single-center study.

METHODS

Sixteen RP patients with pathogenic RHO variants seen at Kyushu University Hospital were investigated. Clinical data including age, best-corrected visual acuity (BCVA) in logarithm of the minimum angle of resolution (logMAR) units, visual field, fundus photography, and optical coherence tomography were retrospectively obtained. Visual outcomes were compared between classical and sector phenotypes and among genetic variants.

RESULTS

The mean age at the first visit was 54.0 ± 15.7 years, with a mean follow-up of 7.6 ± 4.0 years. Fourteen patients (87.5%) showed the classical RP phenotype, of whom four were associated with p.[Pro23Leu] and two had p.[Pro347Leu] variants. In addition, two patients with the sector phenotype harbored p.[Ala164Val] variants. Among the classical RHO-RP patients, the mean BCVA decreased from 0.60 to 1.08 logMAR over the follow-up period (7.4 ± 4.1 years) whereas BCVA was preserved at 0.04 logMAR in sector RHO-RP patients (9.0 ± 3.0 years). Genotype-to-phenotype analysis demonstrated that p.[Pro347Leu] was associated with severe vision loss at an earlier age. Macular complications such as epiretinal membrane and cystoid macular edema were observed in 5 classical RHO-RP patients.

CONCLUSION

p.[Pro23Leu], but not p.[Pro23His], was a frequent variant causing RHO-RP in the Kyushu region of Japan. As reported in previous studies, patients with the p.[Pro347Leu] variant showed a more severe phenotype, and variants causing sector RHO-RP were associated with a good prognosis.

Genetic dissection of non-syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) belongs to a group of pigmentary retinopathies. It is the most common form of inherited retinal dystrophy, characterized by progressive degradation of photoreceptors that leads to nyctalopia, and ultimately, complete vision loss. RP is distinguished by the continuous retinal degeneration that progresses from the mid-periphery to the central and peripheral retina. RP was first described and named by Franciscus Cornelius Donders in the year 1857. It is one of the leading causes of bilateral blindness in adults, with an incidence of 1 in 3000 people worldwide. In this review, we are going to focus on the genetic heterogeneity of this disease, which is provided by various inheritance patterns, numerosity of variations and inter-/intra-familial variations based upon penetrance and expressivity. Although over 90 genes have been identified in RP patients, the genetic cause of approximately 50% of RP cases remains unknown. Heterogeneity of RP makes it an extremely complicated ocular impairment. It is so complicated that it is known as “fever of unknown origin”. For prognosis and proper management of the disease, it is necessary to understand its genetic heterogeneity so that each phenotype related to the various genetic variations could be treated.

Variants identified by next-generation sequencing cause endoplasmic reticulum stress in Rhodopsin-associated retinitis pigmentosa

Background

Rhodopsin (RHO) is the most well-known genetic cause of autosomal dominant retinitis pigmentosa (adRP). This study aimed to investigate the genetic cause of a large Chinese adRP family and assess the pathogenicity of the detected RHO mutant.

Methods

Routine ocular examinations were conducted on all participants. Next-generation sequencing with targeted capture was performed to screen mutations in 179 genes associated with hereditary retinal diseases and 10 candidate genes. Variants detected by NGS were validated by Sanger sequencing and evaluated for pathogenicity. Fragments of mutant and wild-type RHO were cloned into the pEGFP-N1 vector and were transfected into different cell lines to observe the cellular localization of the Rhodopsin-GFP fusion protein and evaluate the expression of endoplasmic reticulum (ER) stress markers. RT-PCR analysis was used to detect transfected the splicing of X box-binding protein 1 (XBP1) mRNA, which is a critical factor affecting ER stress.

Results

Genetic analysis identified a heterozygous missense variant, RHO, c.284 T > C (p.L95P) in this adRP family. Another RHO variant (p.P53R) that we reported previously was also included in further functional assessment. Both misfolded mutant proteins accumulated in the ER in a manner similar to that noted for the classic mutant P23H. Spliced XBP1 was observed in cells transfected with mutants, indicating an increase in ER stress.

Conclusions

Although the p.L95P variant is not a novel change, it was the first variant to be functionally evaluated and reported in Chinese RP patients. The results in our study provide significant evidence to classify the p.L95P mutation as a class II mutation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02110-2.

Genetic landscape of 6089 inherited retinal dystrophies affected cases in Spain and their therapeutic and extended epidemiological implications

Inherited retinal diseases (IRDs), defined by dysfunction or progressive loss of photoreceptors, are disorders characterized by elevated heterogeneity, both at the clinical and genetic levels. Our main goal was to address the genetic landscape of IRD in the largest cohort of Spanish patients reported to date. A retrospective hospital-based cross-sectional study was carried out on 6089 IRD affected individuals (from 4403 unrelated families), referred for genetic testing from all the Spanish autonomous communities. Clinical, demographic and familiar data were collected from each patient, including family pedigree, age of appearance of visual symptoms, presence of any systemic findings and geographical origin. Genetic studies were performed to the 3951 families with available DNA using different molecular techniques. Overall, 53.2% (2100/3951) of the studied families were genetically characterized, and 1549 different likely causative variants in 142 genes were identified. The most common phenotype encountered is retinitis pigmentosa (RP) (55.6% of families, 2447/4403). The most recurrently mutated genes were PRPH2, ABCA4 and RS1 in autosomal dominant (AD), autosomal recessive (AR) and X-linked (XL) NON-RP cases, respectively; RHO, USH2A and RPGR in AD, AR and XL for non-syndromic RP; and USH2A and MYO7A in syndromic IRD. Pathogenic variants c.3386G > T (p.Arg1129Leu) in ABCA4 and c.2276G > T (p.Cys759Phe) in USH2A were the most frequent variants identified. Our study provides the general landscape for IRD in Spain, reporting the largest cohort ever presented. Our results have important implications for genetic diagnosis, counselling and new therapeutic strategies to both the Spanish population and other related populations.

Whole exome sequencing and homozygosity mapping reveals genetic defects in consanguineous Iranian families with inherited retinal dystrophies

Inherited retinal dystrophies (IRDs), displaying pronounced genetic and clinical heterogeneity, comprise of a broad range of diseases characterized by progressive retinal cell death and gradual loss of vision. By the combined use of whole exome sequencing (WES), SNP-array and WES-based homozygosity mapping, as well as directed DNA sequencing (Sanger), we have identified nine pathogenic variants in six genes (ABCA4, RPE65, MERTK, USH2A, SPATA7, TULP1) in 10 consanguineous Iranian families. Six of the nine identified variants were novel, including a putative founder mutation in ABCA4 (c.3260A>G, p.Glu1087Gly), detected in two families from Northeastern Iran. Our findings provide additional information to the molecular pathology of IRDs in Iran, hopefully contributing to better genetic counselling and patient management in the respective families from this country.

Retinal Dystrophies and the Road to Treatment: Clinical Requirements and Considerations

: Retinal dystrophies (RDs) comprise relatively rare but devastating causes of progressive vision loss. They represent a spectrum of diseases with marked genetic and clinical heterogeneity. Mutations in the same gene may lead to different diagnoses, for example, retinitis pigmentosa or cone dystrophy. Conversely, mutations in different genes may lead to the same phenotype. The age at symptom onset, and the rate and characteristics of peripheral and central vision decline, may vary widely per disease group and even within families. For most RD cases, no effective treatment is currently available. However, preclinical studies and phase I/II/III gene therapy trials are ongoing for several RD subtypes, and recently the first retinal gene therapy has been approved by the US Food and Drug Administration for RPE65-associated RDs: voretigene neparvovec-rzyl (Luxturna). With the rapid advances in gene therapy studies, insight into the phenotypic spectrum and long-term disease course is crucial information for several RD types. The vast clinical heterogeneity presents another important challenge in the evaluation of potential efficacy in future treatment trials, and in establishing treatment candidacy criteria. This perspective describes these challenges, providing detailed clinical descriptions of several forms of RD that are caused by genes of interest for ongoing and future gene or cell-based therapy trials. Several ongoing and future treatment options will be described.