The research output of rod-cone dystrophy genetics

Exploring copy number variations in Lebanese families with rod-cone dystrophy reveals a novel deletion in PRPF31 with haploinsufficiency

BACKGROUND AND OBJECTIVES

Rod-cone dystrophy (RCD), also known as retinitis pigmentosa, is the most common group of retinal dystrophies, affecting around 1:4,000 individuals worldwide. In the present work, we performed a copy number variation (CNV) analysis on next-generation sequencing (NGS) data from two Lebanese families with RCD, since no disease-causing mutations were identified through the analysis of single nucleotide variants (SNVs) and insertions/deletions (Indels). NGS, real-time PCR (qPCR), and chromosomal microarray were performed to identify, validate, and delineate the causative CNVs identified in both families involved in this study. Additionally, expression analysis using qPCR and western blotting was conducted to assess the effect of the PRPF31 variant on gene and protein expression levels.

RESULTS

A novel heterozygous deletion (701 bp) spanning exons 6 and 7 of PRPF31 was identified in the first family (F11), resulting in autosomal dominant RCD due to haploinsufficiency. This was confirmed by reduced mRNA levels and the complete absence of protein expression in the affected individuals (F11:III.2 and F11:II.2). In the second family (F26), we identified a previously documented homozygous deletion in the exons 3-19 of MERTK gene, which is responsible for causing severe autosomal recessive RCD.

CONCLUSION

The current study expands the mutational spectrum of PRPF31 and MERTK genes, underscoring the importance of CNVs and haploinsufficiency in RCD etiology. These findings serve as a foundation for future analyses concerning gene augmentation therapies.

Usher Syndrome: New Insights into Classification, Genotype-Phenotype Correlation, and Management

BACKGROUND

Usher syndrome (USH), the most common cause of combined deaf-blindness, is a genetically and phenotypically heterogeneous disorder characterized by congenital hearing impairment and progressive vision loss due to rod-cone dystrophy. Although the original classification in three subtypes (USH I, USH II, and USH III) is still valid, recent findings have changed and widened perspectives in its classification, genotype-phenotype correlations, and management strategies: Objective: This study aims to provide new insights into the classification of Usher syndrome, explore the genotype-phenotype correlations, and review current and emerging management strategies.

METHODS

A comprehensive literature review has been conducted, incorporating data from clinical studies, genetic databases, and patient registries.

RESULTS

Recent studies have led to the identification of several novel pathogenic variants in the USH genes, leading to refined subclassifications of Usher syndrome. Interactions between different genes being part of the network of this ciliopathy have been investigated and new mechanisms unveiled. Significant correlations were found between certain genotypes and the presentation of both auditory and visual phenotypes. For instance, pathogenic variants in the MYO7A gene (USH1B) were generally associated with more severe hearing impairment and earlier onset of retinal dystrophy, if compared to other USH genes-related forms. Other genes, such as USH1G, traditionally considered as causing a specific subtype, can display phenotypic heterogeneity in some patients.

CONCLUSIONS

This review provides insights into a better understanding of Usher syndrome that considers recent findings regarding its genetic causes and clinical features. Precise genotype-phenotype correlations can lead to better genetic counselling, more precise characterization of the natural history of the condition, and a personalized and effective management approach. Recent progress has been made in research into gene-specific therapies that appear promising for improving the quality of life for individuals affected by Usher syndrome.

Overcoming the Challenges to Clinical Development of X-Linked Retinitis Pigmentosa Therapies: Proceedings of an Expert Panel

X-linked retinitis pigmentosa (XLRP) is a rare inherited retinal disease manifesting as impaired night vision and peripheral vision loss that progresses to legal blindness. Although several trials of ocular gene therapy for XLRP have been conducted or are in progress, there is currently no approved treatment. In July 2022, the Foundation Fighting Blindness convened an expert panel to examine relevant research and make recommendations for overcoming the challenges and capitalizing on the opportunities in conducting clinical trials of RPGR-targeted therapy for XLRP. Data presented concerned RPGR structure and mutation types known to cause XLRP, RPGR mutation-associated retinal phenotype diversity, patterns in genotype/phenotype relationships, disease onset and progression from natural history studies, and the various functional and structural tests used to monitor disease progression. Panel recommendations include considerations, such as genetic screening and other factors that can impact clinical trial inclusion criteria, the influence of age on defining and stratifying participant cohorts, the importance of conducting natural history studies early in clinical development programs, and the merits and drawbacks of available tests for measuring treatment outcomes. We recognize the need to work with regulators to adopt clinically meaningful end points that would best determine the efficacy of a trial. Given the promise of RPGR-targeted gene therapy for XLRP and the difficulties encountered in phase III clinical trials to date, we hope these recommendations will help speed progress to finding a cure.

Translational Relevance

Examination of relevant data and recommendations for the successful clinical development of gene therapies for RPGR-associated XLRP.