목적: Auditory neuropathy spectrum disorder (ANSD) is a sensorineural hearing disorder caused by dysfunction of auditory neural conduction. The results of timely cochlear implantation for OTOF-related ANSD (DFNB9) have been reported to be good. Therefore, identifying the causative gene of ANSD, especially OTOF, is an important issue to rehabilitate these patients. 방법:Six sporadic ANSD subjects without anatomical abnormality of the cochlear nerve, including the four subjects that were previously reported to be without detectable OTOF mutation, were included. We performed targeted resequencing (TRS) of known deafness genes and multiphasic bioinformatics analyses of the data that ensured detection of capture failure and structural variations. Exclusion of SNP was also double checked. The TRS data previously obtained from two subjects were re-analyzed. 결과:Through this study, we detected two mutant alleles of OTOF from five (83.3%) of six ANSD subjects. All of the five subjects carried at least one mutant allele carrying p.R1939Q, which resided in the exon with frequent capture failures in TRS. In addition, we detected a structural variation within OTOF from a previously undiagnosed ANSD subject, which was the second structural variation reported in DFNB9 subjects to date. 결론:We identify a strong etiologic homogeneity of pre-lingual ANSD in case of the anatomically normal cochlear nerve in Koreans and now report DFNB9 as the single overwhelming cause. Based on our results, we suggest OTOF mutation as a biomarker which predicts a good prognosis after cochlear implantation in ANSD. Multiphasic analyses of TRS data ensuring detection of capture failure and structural variations are necessary to correctly detect DFNB9 in Korea. This may hold true for other deafness genes.