title: Prediction of cochlear implant performance by genetic mutation: the spiral ganglion hypothesis.
abstract: BACKGROUND
  Up to 7% of patients with severe-to-profound deafness do not benefit from cochlear implantation. Given the high surgical implantation and clinical management cost of cochlear implantation (>$1 million lifetime cost), prospective identification of the worst performers would reduce unnecessary procedures and healthcare costs. Because cochlear implants bypass the membranous labyrinth but rely on the spiral ganglion for functionality, we hypothesize that cochlear implant (CI) performance is dictated in part by the anatomic location of the cochlear pathology that underlies the hearing loss. As a corollary, we hypothesize that because genetic testing can identify sites of cochlear pathology, it may be useful in predicting CI performance.
  
  
  METHODS
  29 adult CI recipients with idiopathic adult-onset severe-to-profound hearing loss were studied. DNA samples were subjected to solution-based sequence capture and massively parallel sequencing using the OtoSCOPE(®) platform. The cohort was divided into three CI performance groups (good, intermediate, poor) and genetic causes of deafness were correlated with audiometric data to determine whether there was a gene-specific impact on CI performance.
  
  
  RESULTS
  The genetic cause of deafness was determined in 3/29 (10%) individuals. The two poor performers segregated mutations in TMPRSS3, a gene expressed in the spiral ganglion, while the good performer segregated mutations in LOXHD1, a gene expressed in the membranous labyrinth. Comprehensive literature review identified other good performers with mutations in membranous labyrinth-expressed genes; poor performance was associated with spiral ganglion-expressed genes.
  
  
  CONCLUSIONS
  Our data support the underlying hypothesis that mutations in genes preferentially expressed in the spiral ganglion portend poor CI performance while mutations in genes expressed in the membranous labyrinth portend good CI performance. Although the low mutation rate in known deafness genes in this cohort likely relates to the ascertainment characteristics (postlingual hearing loss in adult CI recipients), these data suggest that genetic testing should be implemented as part of the CI evaluation to test this association prospectively.
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, University of Iowa Hospitals and Clinics, Iowa City, IA 52242, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Eppsteiner
authors.forename: A Eliot
authors.initials: AE
authors.lastname: Shearer
authors.forename: Michael S
authors.initials: MS
authors.lastname: Hildebrand
authors.forename: Adam P
authors.initials: AP
authors.lastname: Deluca
authors.forename: Haihong
authors.initials: H
authors.lastname: Ji
authors.forename: Camille C
authors.initials: CC
authors.lastname: Dunn
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Black-Ziegelbein
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Casavant
authors.forename: Terry A
authors.initials: TA
authors.lastname: Braun
authors.forename: Todd E
authors.initials: TE
authors.lastname: Scheetz
authors.forename: Steven E
authors.initials: SE
authors.lastname: Scherer
authors.forename: Marlan R
authors.initials: MR
authors.lastname: Hansen
authors.forename: Bruce J
authors.initials: BJ
authors.lastname: Gantz
authors.forename: Richard J H
authors.initials: RJ
authors.lastname: Smith
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold; D002352:Carrier Proteins / Q000235:genetics; D016009:Chi-Square Distribution; D019929:Cochlear Implantation / Q000295:instrumentation*; D003054:Cochlear Implants; D012048:Correction of Hearing Impairment; D004252:DNA Mutational Analysis; D005260:Female; D005786:Gene Expression Regulation; D020022:Genetic Predisposition to Disease; D034381:Hearing Loss / Q000175:diagnosis / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology / Q000534:rehabilitation*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D008875:Middle Aged; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics; D018579:Patient Selection; D019986:Persons with Hearing Disabilities / Q000534:rehabilitation*; D010641:Phenotype; D012697:Serine Endopeptidases / Q000235:genetics; D012720:Severity of Illness Index; D013136:Spiral Ganglion / Q000473:pathology / Q000503:physiopathology*
chemical_list: D002352:Carrier Proteins; C543906:LOXHD1 protein, human; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D012697:Serine Endopeptidases; C409042:TMPRSS3 protein, human