SLC26A4 p.Thr410Met homozygous mutation in a patient with a cystic cochlea and an enlarged vestibular aqueduct showing characteristic features of incomplete partition type I and II.

Mutations of SLC26A4 are associated with incomplete partition type II (IP-II) and isolated enlargement of the vestibular aqueduct (EVA). We experienced a congenitally deaf 6-year-old boy with a rare p.Thr410Met homozygous mutation in SLC26A4 who underwent bilateral cochlear implantation. He had bilateral inner ear malformation, in which the dilated vestibule and EVA were identical to those in IP-II, but the cochlea lacking a bony modiolus resembled that in incomplete partition type I. These results suggest that homozygous mutations in SLC26A4 are always associated with EVA, while the severity of cochlear malformation may vary depending on the type of SLC26A4 mutation.