In this work, we aimed to provide the genetic diagnosis of a large cohort of patients affected with inherited retinal dystrophies (IRDs) from Mexico. Our data add valuable information to the genetic portrait in rare ocular diseases of Mesoamerican populations, which are mostly under-represented in genetic studies. A cohort of 144 unrelated probands with a clinical diagnosis of IRD were analyzed by next-generation sequencing using target gene panels (overall including 346 genes and 65 intronic sequences). Four unsolved cases were analyzed by whole-exome sequencing (WES). The pathogenicity of new variants was assessed by in silico prediction algorithms and classified following the American College of Medical Genetics and Genomics (ACMG) guidelines. Pathogenic or likely pathogenic variants were identified in 105 probands, with a final diagnostic yield of 72.9%; 17 cases (11.8%) were partially solved. Eighteen patients were clinically reclassified after a genetic diagnostic test (17.1%). In our Mexican cohort, mutations in 48 genes were found, with ABCA4, CRB1, RPGR and USH2A as the major contributors. Notably, over 50 new putatively pathogenic variants were identified. Our data highlight cases with relevant clinical and genetic features due to mutations in the RAB28 and CWC27 genes, enrich the novel mutation repertoire and expand the IRD landscape of the Mexican population.

Aims: We aimed to validate the pathogenicity of genetic variants identified in inherited retinal dystrophy (IRD) patients, which were located in non-canonical splice sites (NCSS). Methods: After next generation sequencing (NGS) analysis (target gene panels or whole exome sequencing (WES)), NCSS variants were prioritized according to in silico predictions. In vivo and in vitro functional tests were used to validate their pathogenicity. Results: Four novel NCSS variants have been identified. They are located in intron 33 and 34 of ABCA4 (c.4774-9G>A and c.4849-8C>G, respectively), intron 2 of POC1B (c.101-3T>G) and intron 3 of RP2 (c.884-14G>A). Functional analysis detected different aberrant splicing events, including intron retention, exon skipping and intronic nucleotide addition, whose molecular effect was either the disruption or the elongation of the open reading frame of the corresponding gene. Conclusions: Our data increase the genetic diagnostic yield of IRD patients and expand the landscape of pathogenic variants, which will have an impact on the genotype–phenotype correlations and allow patients to opt for the emerging gene and cell therapies.

Background/Objectives: to report a novel KRT3 Meesmann corneal dystrophy (MECD) mutation and its clinical findings in a Spanish family, thus completing the international database. Case series study. Methods: Two generations of three family members were studied. The clinical ophthalmologic evaluation was made including best-corrected visual acuity (BCVA), biomicroscopy with and without fluorescein, fundoscopy, Schirmer test I, non-invasive break-up time (NiBUT), and esthesiometry. In vivo confocal microscopy (IVCM), anterior segment optical coherence tomography (AS-OCT) with an epithelial map, and genetic analysis were also performed. Results: A novel heterozygous mutation in the KRT3 gene c.1527G>T (p. Glu509Asp) was identified. Biomicroscopy revealed bilateral multiple corneal intraepithelial cysts. IVCM showed numerous and relatively small microcysts (12–32 µm), hyperreflective materials, subepithelial nerve and Bowman’s layer alterations. AS-OCT scan revealed diffuse hyperreflectivity and the epithelial map displayed thickening of the corneal epithelium in the interpalpebral zone (proband: 52–68 µm and father’s proband: 55–71 µm) with a slightly thinned cornea. Conclusions: We identified a new mutation in the KRT3 gene–c.1527G>T (p. Glu509Asp) in a Spanish family with MECD. A comprehensive characterization of the clinical signs, using different techniques, especially an epithelial map, could be useful to diagnose and monitor epithelial changes by quantitative measures. Epithelial map changes provide better understanding of MECD differential epithelial behavior and its progression changes. Larger studies will be necessary to better understand these specific patterns and clinically evaluate new therapies.