Connexin 26 deafness is not always congenital

Abstract

Hearing loss associated with mutations of the GJB2, the gene encoding Connexin 26 (Cx26), is described as a prelingual, bilateral, prevalently stable sensorineural defect ranging in severity from mild to profound. Despite many clinical studies, there is still a limited knowledge about the severity of Cx26 hearing loss at birth, in the postnatal period or in early infancy; some authors have reported about a possible variable age of onset. The aim of this work was to investigate the characteristics of Cx26 hearing loss and test the hypothesis of a postnatal sudden and severe deterioration of the hearing capacity in cases with uncertain age at onset. We have studied 79 children with molecularly documented biallelic Cx26 hearing loss by evaluating longitudinal audiometric characteristics and the results of a questionnaire administered to the parents, regarding the auditory behavior of their children at 3 and 6 months of age. More than 50% of children with profound hearing loss were described as having normal auditory behavior at three months of age, and at least 20% of these children were consistently reported by the parents to maintain normal auditory development up to 6 months of age. None of the studied children showed significant progression in hearing loss from the time of diagnosis through their last follow-up. In a few cases these reports were supported by objective audiometric evaluations. Based on these data, we hypothesize that Cx26 profound hearing loss may be not always congenital, with the possibility of an early window of "functional time" before the final defect is established. The hypothesis of an early auditory input makes timing of detection and intervention critical to minimize the deleterious effects of a functional deprivation. In a near future, the combination of genetic testing with universal neonatal hearing screening and audiological surveillance will provide invaluable information about the natural history of the most frequent sensory defect in infancy and will consequently allow to maximize the quality of intervention.