The a4 subunit colocalizes with the anion exchanger pendrin at the apical side of epithelial cells lining the endolymphatic sac in the inner ear, similar to what is seen in the type-B intercalated cells in the kidney and mice that lack pendrin have sensorineural deafness, similar to humans with Pendred Syndrome (8, 181–183). This evidence concerns the gene SLC26A4 and Pendred syndrome.