FOXI1 and deafness: This hypothesis was based on the studies in Slc26a4Δ/Δ mice that revealed that the enlargement is a key event on the path toward organ failure resulting in deafness and vestibular dysfunction [12], [13], [18] and on studies in Foxi1−/− mice that lack pendrin expression in the endolymphatic sac, develop an enlargement of the inner ear, but express pendrin in the cochlea and the vestibular labyrinth [19].