Phenotype description of a novel DFNA9/COCH mutation, I109T.

OBJECTIVES: This is a report of the audiological and vestibular characteristics of a Dutch DFNA9 family with a novel mutation, I109T, in the LCCL domain of COCH. METHODS: From the family with the novel I109T COCH mutation, audiometric data were collected and analyzed longitudinally. Results were compared to those obtained in previously identified P51 S, G88E, and G87W COCH mutation carriers. Special attention was also given to a comparison of age-related features such as progressive hearing loss and vestibular impairment. RESULTS: A novel mutation (I109T) in COCH segregates with hearing impairment and vestibular dysfunction in the present family. Pure tone thresholds, phoneme recognition scores, and vestibular responses of the I109T mutation carriers were essentially similar to those previously established in P51S, G87W, and G88E mutation carriers. Deterioration of hearing in the I109T mutation carriers started at 43 years of age, and vestibular function deteriorated at least 7 years later. CONCLUSIONS: The phenotype associated with the novel COCH (I109T) mutation is largely similar to that associated with P51S and G88E mutation carriers. However, subtle differences in terms of onset age and rate of progression seem to exist.