Mutational and phenotypic spectrum of OTOF-related auditory neuropathy in Koreans: eliciting reciprocal interaction between bench and clinics

Abstract

Background: While auditory neuropathy spectrum disorder (ANSD) is a heterogeneous disorder and its management quite varies depending upon the etiology, even including self-resolution, OTOF is an important molecular etiology of prelingual ANSD and has emerged as an attractive target for implementation of precision medicine in terms of timing and prognosis prediction of auditory rehabilitation. However, to date, the literature is lacking in the genotype-phenotype relationship of this gene as well as efficient molecular testing strategy in the clinic in many populations and to make things more complicated in Koreans, the most prevalent variant p.Arg1939Gln among Korean ANSD children frequently evaded detection by next generation sequencing (NGS), resulting in delayed genetic diagnosis and late cochlear implantation (CI). The aims of this study are to document the mutational and phenotypic spectrum of OTOF-related ANSD (DFNB9) in the Korean population, further establishing genotype-phenotype correlation and proposing a set of the most commonly found OTOF variants to be screened first.

Methods: Genetic diagnosis through the NGS-based sequencing was made on patients with ANSD in two tertiary hospitals. Genotype and phenotypes of eleven DFNB9 patients were reviewed. For data analysis, Mann-Whitney test and Fisher's exact test were applied.

Results: This study disclosed four prevalent variants in Koreans: p.Arg1939Gln with an allele frequency of 40.9%, p.Glu841Lys (13.6%), p.Leu1011Pro and p.Arg1856Trp (9.1%). Three novel variants (c.4227 + 5G > C, p.Gly1845Glu, and p.Pro1931Thr) were identified. Interestingly, a significant association of p.Arg1939Gln with worse ASSR thresholds was observed despite consistently no ABR response. Ten of 11 DFNB9 patients received CI for auditory rehabilitation, showing favorable outcomes with more rapid improvement on early-CI group (age at CI ≤ 18 mo.) than late-CI group.

Conclusions: This study included the largest Korean DFNB9 cohort to date and proposed a set of the most frequent four OTOF variants, allowing the potential prioritization of exons during Sanger sequencing. Further, a significant association of p.Arg1939Gln homozygotes with poor residual hearing was observed. We may have to suspect p.Arg1939Gln homozygosity in cases of poor auditory thresholds in ANSD children with putative negative OTOF variants solely screened by NGS. Reciprocal feedback between bench and clinics regarding DFNB9 would complement each other.

Keywords: Auditory neuropathy spectrum disorder; Auditory steady-state response; Cochlear implantation; DFNB9; OTOF; Whole exome sequencing.

Fig. 1

Pedigrees of DFNB9 families with molecular genetic diagnosis. Filled symbols represent hearing-impaired individuals, and clear symbols denote those with normal hearing. A diagonal line through a symbol indicates a deceased person and black arrows indicate probands. Designations below each proband represent sex/age. Previously diagnosed families are surrounded by a red border

Fig. 2

Protein domain structures of otoferlin with pathogenic variants in our cohort. Upper panel: Otoferlin contains six C₂ domains (C₂A–C₂F). Missense variants are displayed (top) on the domain structure, and nonsense and splice site variants are located below the domain structure. A red bordered area contains three C₂ domains encoded by short isoform of OTOF. TM: transmembrane domain. Lower panel: Exon–Intron structure of various OTOF isoforms (NM_001287489, NM_194248, NM_194323, NM_194322, NM_004802) locating each variant detected in the study (Captured from UCSC genome browser (https://genome.ucsc.edu/))

Fig. 3

Audiological phenotypes of affected members in ten families with DFNB9. ABR, OAE, and ASSR results are described in order in each patient. Each number on each side of ABR (right in red and left in blue) represents the stimulus intensity calibrated in dB or nHL, which showed no response in all patients. Auditory thresholds of ASSR at 500 Hz are circled in red and blue, each for right and left sides, respectively

Fig. 4

Average CAP scores of CI recipients. Audiologic performances of the two subgroups (early-CI and late-CI) at pre- and post-CI were analyzed longitudinally (p = 0.04 and 0.08 at post-CI 3 mo and 6 mo respectively). CAP is composed of a nonlinear, hierarchical scale with eight categories: (0) Displays no awareness of environmental sounds; (1) awareness of environmental sounds; (2) responds to speech sounds; (3) recognizes environmental sounds; (4) discriminates at least two speech sounds; (5) understands common phrases without lip-reading; (6) understands conversation without lip-reading with a familiar talker; (7) can use telephone with a familiar talker