Combined genetic approaches yield a 48% diagnostic rate in a large cohort of French hearing-impaired patients.

Hearing loss is the most common sensory disorder and because of its high genetic heterogeneity, implementation of Massively Parallel Sequencing (MPS) in diagnostic laboratories is greatly improving the possibilities of offering optimal care to patients. We present the results of a two-year period of molecular diagnosis that included 207 French families referred for non-syndromic hearing loss. Our multi-step strategy involved (i) DFNB1 locus analysis, (ii) MPS of 74 genes, and (iii) additional approaches including Copy Number Variations, in silico analyses, minigene studies coupled when appropriate with complete gene sequencing, and a specific assay for STRC. This comprehensive screening yielded an overall diagnostic rate of 48%, equally distributed between DFNB1 (24%) and the other genes (24%). Pathogenic genotypes were identified in 19 different genes, with a high prevalence of GJB2, STRC, MYO15A, OTOF, TMC1, MYO7A and USH2A. Involvement of an Usher gene was reported in 16% of the genotyped cohort. Four de novo variants were identified. This study highlights the need to develop several molecular approaches for efficient molecular diagnosis of hearing loss, as this is crucial for genetic counselling, audiological rehabilitation and the detection of syndromic forms.

[Usher type I syndrome in children: genotype/phenotype correlation and cochlear implant benefits]. / Syndrome de Usher de type I chez l'enfant: corrlation génotype/phénotype et bénéfice de l'implant cochléaire.

OBJECTIVE: To assess the benefit of cochlear implant in children presenting an Usher type 1 syndrome (speech understanding, speech production intelligibility, academic performance) and to search any correlation between the phenotype and the genotype in this population. MATERIALS AND METHODS: Retrospective case series analysis about 13 implanted Usher type I children. Cochlear implantation was performed from 1995 to 2005. Our population was divided in three groups: group 1 (implantation between 1 and 3 years of age); group 2 (implantation between 4 and 7 years of age) and group 3 (implantation between 14 and 17 years of age). Postoperative speech perception, speech production intelligibility and education settings were evaluated. RESULTS: Molecular genetic analysis was performed in 11 patients and pathogenic mutations were identified in all cases: (mutation in myosin 7A gene in 5 cases; mutation in cadherin 23 gene in 6 cases). Four new mutations 2 in the MYO7A gene and 2 in the CDH23 gene never reported before were found. Walking delay and hearing level were not statistically correlated with the genotype abnormalities found. The speech discrimination skills, the speech production intelligibility and the academic performance were better in the group 1 children than the group 2 children after cochlear implantation. All the children of group 1 but one were in mainstreaming education. Specific language impairment was identified in two children of group 1. The group 3 children could not achieve open-set perceptive tasks after implantation--only closed-set word test can be done and their speech production remained unintelligible after cochlear implantation. CONCLUSION: Molecular analysis of Usher type I syndrome can ascertain the diagnosis in spite of the genetic heterogeneity. In this study, clinical symptoms weren't correlated with genotypic mutations. Speech discrimination skills, speech production quality, and academic performance were correlated with the age at implant.

Survey of the frequency of USH1 gene mutations in a cohort of Usher patients shows the importance of cadherin 23 and protocadherin 15 genes and establishes a detection rate of above 90%.

BACKGROUND: Usher syndrome, a devastating recessive disorder which combines hearing loss with retinitis pigmentosa, is clinically and genetically heterogeneous. Usher syndrome type 1 (USH1) is the most severe form, characterised by profound congenital hearing loss and vestibular dysfunction. OBJECTIVE: To describe an efficient protocol which has identified the mutated gene in more than 90% of a cohort of patients currently living in France. RESULTS: The five genes currently known to cause USH1 (MYO7A, USH1C, CDH23, PCDH15, and USH1G) were tested for. Disease causing mutations were identified in 31 of the 34 families referred: 17 in MYO7A, 6 in CDH23, 6 in PCDH15, and 2 in USH1C. As mutations in genes other than myosin VIIA form nearly 50% of the total, this shows that a comprehensive approach to sequencing is required. Twenty nine of the 46 identified mutations were novel. In view of the complexity of the genes involved, and to minimise sequencing, a protocol for efficient testing of samples was developed. This includes a preliminary linkage and haplotype analysis to indicate which genes to target. It proved very useful and demonstrated consanguinity in several unsuspected cases. In contrast to CDH23 and PCDH15, where most of the changes are truncating mutations, myosin VIIA has both nonsense and missense mutations. Methods for deciding whether a missense mutation is pathogenic are discussed. CONCLUSIONS: Diagnostic testing for USH1 is feasible with a high rate of detection and can be made more efficient by selecting a candidate gene by preliminary linkage and haplotype analysis.