Genetic Screening of the Usher Syndrome in Cuba

Genetic Landscape of Hearing Loss in the Caribbean: A Narrative Review

The Caribbean region has a diverse population of about 40 million people, spread over 13 sovereign states. This review aims to describe the existing studies on hereditary hearing loss (HL) in the Caribbean population. We systematically reviewed scientific articles on HL prevalence, genetic causes, technology use, and environmental effects in Caribbean nations and the Caribbean diaspora in the United States. Key findings show that HL rates, with diverse genetic variables, vary across Puerto Rico, Cuba, and the Dominican Republic. Local resources and technology have been used to diagnose HL, particularly in rural areas. Environmental factors tend to affect HL prevalence in various regions. This literature review of Caribbean-focused studies helps guide future research and healthcare strategies, particularly concerning genetic drift caused by migration to the United States. Understanding these factors can help diagnose and treat HL in America's diverse population.

Genetic characteristics of suspected retinitis pigmentosa in a cohort of Chinese patients

The study aimed to screen for the causative variants in Chinese patients with suspected retinitis pigmentosa (RP). A cohort of 75 unrelated Chinese patients with a clinical diagnosis of RP and their available family members were enrolled in this study. Genomic DNA of all subjects was extracted and whole-exome sequencing (WES) was applied. Candidate variants were identified, and minigene assays were conducted to evaluate the pathogenicity of novel splicing variants. Totally, the diagnostic yield was 44 % (33/75) and 16 novel variants that had not been reported previously were found. Among the genetically solved 33 cases, 31 patients were identified as carrying causative variants of RP and 2 patients carried pathogenic variants implicated in other retinal diseases. USH2A, CYP4V2, and RPGR were the most common causative genes, accounting for about half of the genetically solved cases. Moreover, minigene assays validated that the novel splicing variants were detrimental. Additionally, 9 patients carried a single deleterious heterozygous variant in 6 genes with autosomal recessive hereditary patterns, and no corresponding copy number variants (CNVs) was detected. The findings of this study revealed the genetic landscape of RP in China and provided guidance for clinicians.

Review of Genotype-Phenotype Correlations in Usher Syndrome

Usher syndrome (USH) encompasses a group of clinically and genetically heterogenous disorders defined by the triad of sensorineural hearing loss (SNHL), vestibular dysfunction, and vision loss. USH is the most common cause of deaf blindness. USH is divided clinically into three subtypes-USH1, USH2, and USH3-based on symptom severity, progression, and age of onset. The underlying genetics of these USH forms are, however, significantly more complex, with over a dozen genes linked to the three primary clinical subtypes and other atypical USH phenotypes. Several of these genes are associated with other deaf-blindness syndromes that share significant clinical overlap with USH, pointing to the limits of a clinically based classification system. The genotype-phenotype relationships among USH forms also may vary significantly based on the location and type of mutation in the gene of interest. Understanding these genotype-phenotype relationships and associated natural disease histories is necessary for the successful development and application of gene-based therapies and precision medicine approaches to USH. Currently, the state of knowledge varies widely depending on the gene of interest. Recent studies utilizing next-generation sequencing technology have expanded the list of known pathogenic mutations in USH genes, identified new genes associated with USH-like phenotypes, and proposed algorithms to predict the phenotypic effects of specific categories of allelic variants. Further work is required to validate USH gene causality, and better define USH genotype-phenotype relationships and disease natural histories-particularly for rare mutations-to lay the groundwork for the future of USH treatment.

Homology modeling and global computational mutagenesis of human myosin VIIa

Usher syndrome type 1B (USH1B) is a genetic disorder caused by mutations in the unconventional Myosin VIIa (MYO7A) protein. USH1B is characterized by hearing loss due to abnormalities in the inner ear and vision loss due to retinitis pigmentosa. Here, we present the model of human MYO7A homodimer, built using homology modeling, and refined using 5 ns molecular dynamics in water. Global computational mutagenesis was applied to evaluate the effect of missense mutations that are critical for maintaining protein structure and stability of MYO7A in inherited eye disease. We found that 43.26% (77 out of 178 in HGMD) and 41.9% (221 out of 528 in ClinVar) of the disease-related missense mutations were associated with higher protein structure destabilizing effects. Overall, most mutations destabilizing the MYO7A protein were found to associate with USH1 and USH1B. Particularly, motor domain and MyTH4 domains were found to be most susceptible to mutations causing the USH1B phenotype. Our work contributes to the understanding of inherited disease from the atomic level of protein structure and analysis of the impact of genetic mutations on protein stability and genotype-to-phenotype relationships in human disease.

Targeted Next-Generation Sequencing Identified Novel Compound Heterozygous Variants in the CDH23 Gene Causing Usher Syndrome Type ID in a Chinese Patient

Usher syndrome includes a group of genetically and clinically heterogeneous autosomal recessive diseases, such as retinitis pigmentosa (RP) and sensorineural hearing loss. Usher syndrome type I (USHI) is characterized by profound hearing impairment beginning at birth, vestibular dysfunction, and unintelligible speech in addition to RP. The relationships between the Usher syndrome causing genes and the resultant phenotypes of Usher syndrome have not yet been fully elucidated. In the present study, we recruited a Chinese family with Usher syndrome and conducted paneled next-generation sequencing, Sanger sequencing, segregation analysis, and expression profile analysis. The functional effects of the identified cadherin-related 23 (CDH23) pathogenic variants were analyzed. The M101 pedigree consisted of a proband and seven family members, and the proband was a 39-year-old Chinese male who claimed that he first began to experience night blindness 11 years ago. We revealed novel, missense compound heterozygous variants c. 2572G > A (p.V858I) and c. 2891G > A (p.R964Q) in the CDH23 gene, which co-segregated with the disease phenotype causing Usher syndrome type ID (USH1D) in this Chinese pedigree. CDH23 mRNA was highly expressed in the retina, and this protein was highly conserved as revealed by the comparison of Homo sapiens CDH23 with those from nine other species. This is the first study to identify the novel, missense compound heterozygous variants c. 2572G > A (p.V858I) and c.2891G > A (p.R964Q) of CDH23, which might cause USH1D in the studied Chinese family, thereby extending CDH23 mutation spectra. Identifying CDH23 pathogenic variants should help in the detailed phenotypic characterization of USH1D.