Molecular genetics applied to clinical practice: the Cx26 hearing impairment

Mutations in the Cx26/GJB2 gene account for a large proportion of pre-lingu al hearing impairment with a prevalence up to 50% in autosomal recessive ca ses and a still undefined prevalence in sporadic cases. Ninety-four subject s affected by non-syndromal sensorineural hearing impairment (NSHI) were en rolled in the study. The patients had either a family history of childhood hearing deficit or represented sporadic cases. The risk of an acquired caus e of the deficit has been carefully excluded. Audiological characteristics were investigated. Cx26 mutations were found in 50% of subjects. Seventy-th ree per cent of mutations in this gene were 35delG, with significant geogra phical variations. In 7% of the putative Cx26 alleles no mutations were det ected either in the coding region or in the non-coding exon 1. Cx26 hearing impairment involves all frequencies, is of variable severity, and is very rarely progressive and most frequently symmetrical between the two ears. Th e high occurrence of this type of pre-lingual hearing impairment argues for modification of the protocols used to investigate the aetiology of childho od hearing impairment. Early screening for Cx26 mutations in all patients w ith non-syndromal familial and sporadic permanent childhood hearing impairm ent seems justified.