Probable ion channel required for the normal function of cochlear hair cells. Interacts with TOMT. The interaction of TMC1 and TMC2 with TOMT is required for the transportation of TMC1/2 into the stereocilia of hair cells. Interacts (via N-terminus) with both isoforms CD1 and CD3 of PCDH15. Localized to the stereocilia of the cochlear hair cells. Detected in cochlear inner and outer hair cells and in neurosensory epithelia of the vestibular end organs. Also expressed in cortex, cerebellum, eye, colon, ovary and testis. Expressed at low, constant levels in temporal bone from embryonic day 14 to day 1 after birth. Increases by 8 to 16-fold at day 5, 10 and 20 and continues to be expressed up to day 90. Defects in Tmc1 are the cause of the dominant deaf mutant Beethoven (BTH). Heterozygotes show progressive hair-cell degeneration from day 20 onwards, leading to severe depletion of inner hair cells and scattered loss of outer hair cells, and progressive loss of the Preyer reflex from around day 30. Homozygotes show almost complete degeneration of inner hair cells, and little or no Preyer reflex at any age. Defects in Tmc1 are the cause of recessive deaf mutant dn. The dn mutant shows profound deafness with degeneration of the organ of Corti, stria vascularis, and occasionally the saccular macula, starting at about 10 days after birth (PubMed:11850618). Belongs to the TMC family.