Dysfunction of the genes contributing to homeostasis of the cochlear endolymph, such as ATP1A3 [5], KCNQ1 [6], and KCNE1 [7], leads to CAPOS (cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss) syndrome (MIM: 601338), Jervell and Lange-Nielsen syndrome (JLNS) 1 (MIM: 220400), and JLNS2 (MIM: 612347), respectively, which all have hearing loss as a major clinical feature. The gene discussed is KCNE1; the disease is Leber hereditary optic neuropathy.