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.