This retrospective study describes the phenotype associated with the single most common cause of genetic hearing loss. The frequency of childhood deafness is estimated at 1/500. Half of this hearing loss is genetic and ∼80% of genetic hearing loss is nonsyndromic and inherited in an autosomal recessive manner. Approximately 50% of childhood nonsyndromic recessive hearing loss is caused by mutations in the connexin 26 (Cx26) gene (GJB2/DFNB1), making it the most common form of autosomal recessive nonsyndromic hearing loss with a carrier rate estimated to be as high as 2.8%. One mutation, 35delG, accounts for ∼75% to 80% of mutations at this gene.
Hearing loss was examined in 46 individuals from 24 families who were either homozygous or compound heterozygous for Cx26 mutations. A subset of these individuals were examined for vestibular function, otoacoustic emissions, auditory brainstem response, temporal bone computed tomography, electrocardiography, urinalyses, dysmorphology, and thyroid function.
Although all persons had hearing impairment, no consistent audiologic phenotype was observed. Hearing loss varied from mild-moderate to profound, even within the group of families homozygous for the common mutation 35delG, suggesting that other factors modify the phenotypic effects of mutations in Cx26. Furthermore, the hearing loss was observed to be progressive in a number of cases. No associations with inner ear abnormality, thyroid dysfunction, heart conduction defect, urinalyses, dysmorphic features, or retinal abnormality were noted.
Newborns with confirmed hearing loss should have Cx26 testing. Cx26 testing will help define a group in which ∼60% will have profound or severe-profound hearing loss and require aggressive language intervention (many of these patients will be candidates for cochlear implants).