Otoferlin is a calcium sensor protein critical for the transmission of the signal from inner hair cells (IHCs) to the spiral ganglion neurons (SGNs), and it is encoded by the OTOF gene. Pathogenic biallelic loss of function variations in OTOF result in failure of synaptic transmission, causing autosomal recessive deafness 9 (DFNB9), which is a congenital severe-to-profound auditory neuropathy.