Whole-Exome Sequencing Targeting a Gene Panel for Sensorineural Hearing Loss: The First Portuguese Cohort Study.

Next-generation sequencing (NGS) technologies revolutionized the molecular diagnosis of sensorineural hearing loss (SNHL) and are now a standard of care. In this study, 71 Portuguese probands with hereditary SNHL were assessed by whole-exome sequencing (WES) targeting a panel of 158 genes related to SNHL, aiming to evaluate the diagnostic yield of this methodological approach and to report the spectrum of variants. Patients with either nonsyndromic or syndromic SNHL were included. Also, patients were previously screened for variants in the GJB2 gene and for duplications/deletions in the GJB6 gene. Causative variants in 11 different genes were identified in 15 (21.1%) out of 71 probands, 5 of which had associated syndromes. In 6 other patients (8.5%), presumptive causative variants were identified in MYO15A, TMIE, TBC1D24, SPMX, GJB3, PCDH15, and CDH23 genes, uncovering a potential case of digenic Usher syndrome. The study was inconclusive in 20 probands (28.2%), in 19 due to lack of segregation analysis and in one due to uncertain phenotype-genotype matching. In the remaining 30 patients (42.3%) no potentially causative variants were identified. The diagnostic yield did not significantly vary according to the age of hearing-impairment onset. As the first study on the application of NGS technologies in SNHL based on a Portuguese cohort, our results may contribute to characterize the spectrum of variants related to SNHL in the Portuguese population. Additionally, the present study provides new insights into the contribution of MYO3A, TECTA, EDNRB, TBC1D24, and GJB3 genes to SNHL. For the significant number of undiagnosed patients, reanalysis of WES data - either for a broader gene panel or in a non-targeted approach - may be considered.

GJB2: Frequency of the Less Common Variants in a Sample of the Portuguese Population.

INTRODUCTION: Sequence variants in the GJB2 gene account for up to 50% of cases of non-syndromic sensorineural hearing loss in the Caucasian population. In this study, we report the frequency of the less common variants of the GJB2 gene in a Portuguese sample and compare these frequencies with those of a group of hearing-impaired patients. MATERIAL AND METHODS: In order to select the less common GJB2 variants, 147 hearing-impaired patients followed in Centro Hospitalar Universitário de São João were evaluated. Afterwards, the presence of those variants was tested in 360 individuals from Generation 21. RESULTS: The patient assessment enabled the selection of 11 GJB2 variants. Of those, 10 were investigated in Generation 21 participants, with only four being detected, in heterozygosity: p.Phe83Leu, p.Arg127His, p.Val153Ile and p.Asn206Ser, with the allelic frequencies (95% confidence interval) of 0.14% (0.01% - 0.87%), 0.28% (0.01% - 1.08%), 0.97% (0.43% - 2.04%) and 0.14% (0.01% - 0.88%), respectively. Two variants, p.Val37Ile and p.Val95Met, were more frequent in the patients' group with statistical significance. DISCUSSION: Our results allow for the p.Arg127His and p.Val153Ile variants to comply with polymorphism criteria and support the pathogenicity of p.Val37Ile and p.Val95Met variants. Moreover, two cases of moderate hearing loss were explained by the p.Val37Ile/p. Asn206Ser genotype, substantiating both the pathogenicity of such variants and the hypothesis that compound heterozygosity with p.Ans206Ser is associated with mild-moderate genotypes. CONCLUSION: Understanding the role of the variants is essential in order to provide genetic counselling to patients and their families. We explored a set of uncommon GJB2 variants that comprised 12% of the hearing-impaired patients in this study, supporting the relevance of their description.

Introdução: As mutações no gene GJB2 são responsáveis por mais de 50% dos casos de hipoacusia neurossensorial não sindrómica na população caucasiana. Neste estudo, reporta-se a frequência das variantes menos comuns do gene GJB2 numa amostra da população portuguesa, comparando-se com a dos doentes com hipoacusia seguidos na consulta de Genética. Material e Métodos: Para seleção das variantes menos frequentes do gene GJB2, avaliaram-se 147 doentes com hipoacusia seguidos na consulta de Genética ­ Doenças Hereditárias do Ouvido do Centro Hospitalar Universitário de São João. A presença dessas variantes foi depois testada em 360 indivíduos da Geração 21. Resultados: A avaliação dos doentes com hipoacusia permitiu selecionar 11 variantes. Dessas, 10 foram pesquisadas nos indivíduos da Geração 21, identificando-se apenas quatro, em heterozigotia: p.Phe83Leu, p.Arg127His, p.Val153Ile e p.Asn206Ser, com frequências alélicas (intervalo de confiança 95%) de 0,14% (0,01% - 0,87%), 0,28% (0,01% - 1,08%), 0,97% (0,43% - 2,04%) e 0,14% (0,01% - 0,88%), respetivamente. Duas variantes, p.Val37Ile e p.Val95Met, mostraram-se mais frequentes nos doentes com hipoacusia de forma estatisticamente significativa. Discussão: Estes resultados permitem considerar as variantes p.Arg127His e p.Val153Ile como polimorfismos e apoiam a patogenicidade das variantes p.Val37Ile e p.Val95Met. Note-se ainda que dois casos de hipoacusia moderada foram justificados pelo genótipo p.Val37Ile/p.Asn206Ser, apoiando a patogenicidade de tais variantes e corroborando a hipótese de que heterozigotias compostas com a p.Asn206Ser cursam com fenótipo ligeiro-moderado. Conclusão: O conhecimento da patogenicidade das variantes é fundamental para o aconselhamento genético dos doentes e respetivas famílias. No seu conjunto, as variantes do gene GJB2 analisadas estavam presentes em 12% dos doentes, reiterando a relevância do seu estudo.