Possible explanations for these heterozygous cases are 1) the co-existence of copy number variations, 2) the existence of a second mutation in the exonic region that could not be covered in this study or in regulatory region of OTOF, which was not explored, 3) the contribution to hearing loss of an additional modulatory gene, and 4) the existence of a mutation in another gene (DIAPH3, AIFM1, ATP1A3 and mitochondrial 12SrRNA) which causes non-syndromic ANSD not examined in this study [18], so that the patients were just coincidental carriers of the OTOF mutations. Here, OTOF is linked to auditory neuropathy.