GJB2 Variants and Auditory Outcomes among Filipino Cochlear Implantees

Objectives: To determine the prevalence of gap junction beta-2 (GJB2) or connexin 26 variants in Filipino cochlear implantees, and to describe radiologic findings, audiologic results and auditory performance after cochlear implantation (CI). Methods: Thirty cochlear implantees with unknown etiology of congenital severe-to-profound hearing loss and 30 controls provided venous blood samples for study. Radiologic evidence of temporal bone abnormalities, residual hearing status and post-CI auditory performance are described. Statistical analysis was performed for hearing thresholds before and after CI and for Parent Evaluation of Auditory/Oral Performance in Children (PEACH) scores based on the presence of cochleovestibular anomalies, age at CI and time since CI. Genomic DNA was extracted from venous blood, PCR-amplified and sequenced for GJB2 variants. Results: One patient was compound heterozygous (c.[35delG];[235delC]) for GJB2 variants. The variants p.Gly4Asp, p.Val27Ile and p.Val37Ile were identified in both patients and controls, including 2 implantees who were homozygous for p.Val27Ile and p.Val37Ile. No significant association was found between post-CI improvement in threshold or PEACH scores and the following variables: age at CI, duration of hearing aid use prior to CI, presence of cochleovestibular anomalies and completeness of electrode insertion. Although no significant change in audiometric thresholds due to time since CI was detected, PEACH scores were significantly improved with longer implant use at all conditions (quiet, noise and overall; p < 0.05). Conclusions: The prevalence of causal GJB2 variants in Filipino cochlear implantees is low (3.3%). Within this population, the allele frequency of the p. Val37Ile variant in patients and controls is >10%, which supports a nonpathogenic role for this variant. The low prevalence of GJB2 variants precluded any association testing with CI outcome, although our results suggest better auditory outcome with longer CI use. Future genetic studies within the Filipino population should be able to control for population admixture. Copyright (C) 2013 S.Karger AG, Basel