Subgroups of enlarged vestibular aqueduct in relation to SLC26A4 mutations and hearing loss.

OBJECTIVES/HYPOTHESIS To investigate possible association of hearing loss and SLC26A4 mutations with the subgroups of enlarged vestibular aqueduct (EVA) morphology in Japanese subjects with hearing loss. STUDY DESIGN Retrospective multicenter study. METHODS Forty-seven subjects who had vestibular aqueduct with midpoint diameter >1 mm by computed tomography of the temporal bone were enrolled at multiple sites across Japan, and DNA samples and clinical data were collected. EVA morphology was classified into four subgroups by the pattern of enlargement: aperture, aperture and midpoint, midpoint, and borderline enlargement. Venous blood DNA samples were subjected to polymerase chain reaction-based direct sequencing of all exons and exon-intron boundaries of the SLC26A4. RESULTS Four novel SLC26A4 mutations were identified in the present study. SLC26A4 mutations were detected in almost all subjects with aperture, aperture and midpoint, and midpoint enlargement. In contrast, 71% of subjects with borderline enlargement had no SLC26A4 mutation. No significant difference was found in the distribution of truncating and nontruncating SLC26A4 mutations between the EVA subgroups. In addition, no significant correlation was observed between the EVA subgroups and hearing levels, incidence of hearing fluctuation, or progression of hearing loss. CONCLUSIONS Subgroups of EVA morphology were significantly correlated with the presence or absence of SLC26A4 mutation. In a subgroup analysis of subjects with SLC26A4 mutations, however, differences in the EVA subgroups were not correlated with SLC26A4 genotypes or characteristics of hearing loss. LEVEL OF EVIDENCE NA.