Distinct vestibular phenotypes in DFNA9 families with COCH variants

Mutations of COCH can cause hearing loss and less frequently vestibular symptoms. However, vestibular phenotypes, especially in terms of the location of specific variants are not well documented yet. In this study, a retrospective and prospective cohort survey was performed in two tertiary referral hospitals to demonstrate vestibular phenotypes of DFNA9 subjects with a focus on the relationship with the location of COCH mutations. Two DFNA9 subjects were recruited from the previously collected cohort, each segregating p.G38D and p.C162Y of the COCH gene. Another two DFNA9 families were newly detected by targeted resequencing of known 129 deafness genes (TRS-129). These two families segregated the p.G38D variant of the COCH gene as the causative mutation, making p.G38D the most frequent COCH mutation in our Korean cohorts. Regarding the detailed clinical phenotype of the four DFNA9 families with documented vestibular phenotypes, we were able to classify them into two groups: one (p.C162Y variant) with a Meniere's disease (MD)-like phenotype and the other three (p.G38D variant) with significant bilateral vestibular loss without any definite MD symptoms. Distinct vestibular phenotypes depending on the location of COCH mutations were demonstrated, and this study correlates a genotype of p.G38D in COCH to the phenotype of bilateral total vestibular loss, therefore expanding the vestibular phenotypic spectrum of DFNA9 to range from bilateral vestibular loss without episodic vertigo to MD-like features with devastating episodic vertigo. In addition, the p.G38D variant of the COCH gene is suggested to be a frequent cause of progressive audiovestibular dysfunction in Koreans eventually requiring cochlear implantation.