ObjectiveTo report the clinical, auditory, and vestibular characteristics of a nonsyndromic otovestibular dysfunction in a large Belgian family caused by a missense mutation of the DFNA9 gene: COCH.Study DesignRetrospective study of the clinical, audiologic, and vestibular data of 60 genetically affected cases.SettingTertiary referral center.PatientsAll members of a Belgian kindred who carry the genetic (P51S) defect linked to the inherited hearing and vestibular impairment.InterventionsDiagnostic otologic, audiometric, and vestibular analysis and imaging.Main Outcome MeasuresPure tone audiometry, supraliminary audiometry. and vestibular investigation.ResultsThe autosomal dominant inherited impairment was characterized by peripheral degeneration of the inner ear, leading to total deafness and bilateral vestibular areflexia.ConclusionsThe genetically affected persons of a Belgian family shared a progressive sensorineural hearing loss starting between the third and sixth decade. Vestibular symptoms started at about the same age as the hearing loss. The vestibular symptoms consisted of instability in darkness, a tendency to fall sideways, light-headiness, a drunken feeling, and attacks of vertigo. Most of the patients reported tinnitus, and half of them reported pressure in the ears. Clinically, 9 of the 60 patients met the criteria for definite Ménière's disease, and another 13 and 17 patients met the criteria for probable or possible Ménière's disease, respectively. All 9 were older than the age of 35, but only 1 was older than 55 years, so more than 30% of the patients were between 35 and 55 years old.A specific pattern could be recognized in the evolution of the otovestibular impairment. Under the age of 35 years, almost all the affected family members had normal hearing, whereas above the age of 55 years, the hearing loss was at least moderate, and vestibular hypofunction occurred. In between, there was a transition period of two to three decades, when deterioration of the cochleovestibular function occurred, with a temporary audiometric and vestibular asymmetry.