(A) At postnatal day 13, auditory brainstem response (ABR) thresholds to broadband click stimuli are equivalent in Tmtc4-KO (red squares), Het (blue triangles), and WT (black circles) littermates. Tmtc4-KO mice progress to profound deafness by P26 (n = 4 for each genotype). (B) Hearing loss in P26 Tmtc4-KO mice is present in response to both broadband click and a range of pure-tone frequencies (n = 4 for each genotype). (C) Distortion-product otoacoustic emissions (DPOAEs) measured at different frequencies demonstrate cochlear dysfunction in P26 Tmtc4-KO mice (n = 4 for each genotype). (D) ABR waveforms in P26 Tmtc4-KO and WT littermates demonstrate absent ABR responses to click stimuli at multiple sound pressure levels (SPL) in KO mice. Traces representative of at least 4 experiments. Data are mean ± SD. *P < 0.01, **P < 0.001 by 2-tailed, unpaired t test.