RESUMO
PURPOSE: Pathogenic variants of the gap junction beta 2 (GJB2) gene are responsible for about 50% of hereditary non-syndromic sensorineural hearing loss (NSHL). In this study, we report mutation frequency and phenotype comparison of different GJB2 gene alterations in Hungarian NSHL patients. METHODS: The total coding region of the GJB2 gene was analyzed with Sanger or NGS sequencing for 239 patients with NSHL and 160 controls. RESULTS: Homozygous and compound heterozygous GJB2 mutations were associated with early onset serious clinical phenotype in 28 patients. In 24 patients, two deletion or nonsense mutations were detected in individuals with mainly prelingual NSHL. In compound heterozygous cases, a combination of deletion and missense mutations associated with milder postlingual NSHL. A further 25 cases harbored single heterozygous GJB2 mutations mainly associated with later onset, milder clinical phenotype. The most common mutation was the c.35delG deletion, with 12.6% allele frequency. The hearing loss was more severe in the prelingual groups. CONCLUSION: The mutation frequency of GJB2 in the investigated cohort is lower than in other European cohorts. The most serious cases were associated with homozygous and compound heterozygous mutations. In our cohort the hearing impairment and age of onset was not altered between in cases with only one heterozygous GJB2 mutation and wild type genotype, which may exclude the possibility of autosomal dominant inheritance. In early onset, severe to profound hearing loss cases, if the GJB2 analysis results in only one heterozygous alteration further next generation sequencing is highly recommended.
