Audiologic evidence for further genetic heterogeneity at DFNA2

A large American family has been mapped to the DFNA2 locus. However, mutation screening of CX31 and KCNQ4, the two genes associated with deafness at this locus, did not identify any mutations. The purpose of this report was to characterize the otologic and audiometric phenotype of this large American family with non-syndromic, autosomal-dominant sensorineural hereditary hearing impairment (HHI). Anamnestic data were obtained, pure-tone audiometry was performed and transient-evoked otoacoustic emissions were recorded. The findings in affected family members were compared to those in unaffected family members and to the respective p50 thresholds of the normal age-matched population. Mutational analysis of the CX26 gene was also performed. The affected members of this family demonstrated progressive symmetric sensorineural hearing impairment. The hearing loss was downward sloping, with mild-to-moderate loss in the low and mid frequencies and severe-to-profound loss in frequencies > 4,000 Hz. The onset of disease was predominantly in the first or early in the second decade. Hearing impairment progressed at approximately 1 dB per year across all frequencies. Transient-evoked otoacoustic emissions revealed a minimal response over all frequencies in affected members but robust responses in all unaffected members. Mutation in the CX26 gene was not present. The affected frequencies observed in this family were similar to those in the original family mapped to DFNA2; however, the age of onset of disease was different and the hearing loss progressed at a slower rate. Therefore, this family provides clinical evidence of genetic heterogeneity at the DFNA2 locus and can serve as a model for age-related hearing loss.