Auditory responses in cochlear implant users with and without GJB2 deafness.
OBJECTIVE
It is reasonable to suppose that the pattern of sensorineural damage along the length of the cochlea depends on the etiology of a hearing loss (HL). In GJB2-related deafness, we hypothesize that gap junction deficits are uniformly distributed and will result in similar damage along the length of the cochlea as compared with non-GJB2 subjects. We assessed this by measuring patterns of neural activity and hearing from apical versus basal cochlear implant electrode regions.


METHODS
This was a prospective, blind, controlled study.


METHODS
Blood from 301 pediatric cochlear implant users was analyzed for mutations in GJB2 by direct sequencing. After exclusion of patients with monoallelic GJB2 mutations, associated syndromes, or risk factors for HL that were not congenital, 39 children with biallelic GJB2 mutations and 58 without GJB2 mutations were evaluated. Hearing was measured before implantation at frequencies ranging from 250 Hz to 8 kHz. After implantation, neural activity at the apical and basal ends of the implanted array was measured using electrically evoked compound action potentials of the auditory nerve (ECAPs) and evoked stapedius reflexes (ESRs).


RESULTS
GJB2 and non-GJB2 groups were not significantly different with respect to sex, age at implantation, duration of auditory deprivation, hearing aid use, duration of aided hearing, ear implanted, implant model, or depth of insertion (P>.05). Children with GJB2-related HL had greater similarities between low- and high-frequency residual hearing and between neural activity electrically evoked at apical and basal regions of the cochlea as compared with children with non-GJB2-related HL who demonstrated larger deficits in basal regions.


CONCLUSIONS
Results suggest more consistent spiral ganglion survival along the length of the cochlea in GJB2-related HL as compared with non-GJB2-related HL, which appears to involve a decreasing gradient of spiral ganglion survival from the apex to the base of the cochlea. Our findings support our premise that in GJB2-related HL, dysfunction of gap junctions likely occurs to a similar degree in the apical and basal regions of the cochlea. This knowledge might be used to customize implantable devices for patients with HL in the future.
Department of Otolaryngology-Head and Neck Surgery and the Molecular Genetics Laboratory, The Hospital for Sick Children, Toronto, Ontario, Canada. evan.propst@utoronto.ca
Evan Jon
EJ
Propst
Blake C
BC
Papsin
Tracy L
TL
Stockley
Robert V
RV
Harrison
Karen A
KA
Gordon
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D019929:Cochlear Implantation; D000072259:Connexin 26; D017630:Connexins / Q000235:genetics*; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D017629:Gap Junctions / Q000502:physiology; D006319:Hearing Loss, Sensorineural / Q000235:genetics* / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D007223:Infant; D008297:Male; D009154:Mutation; D013136:Spiral Ganglion / Q000503:physiopathology
D017630:Connexins; C000607042:GJB2 protein, human; D000072259:Connexin 26