Novel compound heterozygous mutations in the OTOF Gene identified by whole-exome sequencing in auditory neuropathy spectrum disorder

Abstract

Background: Many hearing-loss diseases are demonstrated to have Mendelian inheritance caused by mutations in single gene. However, many deaf individuals have diseases that remain genetically unexplained. Auditory neuropathy is a sensorineural deafness in which sounds are able to be transferred into the inner ear normally but the transmission of the signals from inner ear to auditory nerve and brain is injured, also known as auditory neuropathy spectrum disorder (ANSD). The pathogenic mutations of the genes responsible for the Chinese ANSD population remain poorly understood.

Methods: A total of 127 patients with non-syndromic hearing loss (NSHL) were enrolled in Guangxi Zhuang Autonomous Region. A hereditary deafness gene mutation screening was performed to identify the mutation sites in four deafness-related genes (GJB2, GJB3, 12S rRNA, and SLC26A4). In addition, whole-exome sequencing (WES) was applied to explore unappreciated mutation sites in the cases with the singularity of its phenotype.

Results: Well-characterized mutations were found in only 8.7% (11/127) of the patients. Interestingly, two mutations in the OTOF gene were identified in two affected siblings with ANSD from a Chinese family, including one nonsense mutation c.1273C > T (p.R425X) and one missense mutation c.4994 T > C (p.L1665P). Furthermore, we employed Sanger sequencing to confirm the mutations in each subject. Two compound heterozygous mutations in the OTOF gene were observed in the two affected siblings, whereas the two parents and unaffected sister were heterozygous carriers of c.1273C > T (father and sister) and c.4994 T > C (mother). The nonsense mutation p.R425X, contributes to a premature stop codon, may result in a truncated polypeptide, which strongly suggests its pathogenicity for ANSD. The missense mutation p.L1665P results in a single amino acid substitution in a highly conserved region.

Conclusions: Two mutations in the OTOF gene in the Chinese deaf population were recognized for the first time. These findings not only extend the OTOF gene mutation spectrum for ANSD but also indicate that whole-exome sequencing is an effective approach to clarify the genetic characteristics in non-syndromic ANSD patients.

Keywords: Auditory neuropathy spectrum disorder; Heterozygous mutations; OTOF gene; Whole-exome sequencing.

Fig. 1

Pedigree and sequence analysis of OTOF mutations in the ANSD family. a In a Chinese ANSD family, compound heterozygous mutations c.1273 C > T and c.4994 T > C were observed in both affected siblings (II:1 and II:3); b One heterozygous mutation c.1273 C > T was observed in the sister (II:2). The c.1273 C > T heterozygous mutation is from the father (I:1), and the other heterozygous c.4994 T > C mutation is from the mother (I:2)

Fig. 2

Audiologic tests of subject II:3. Subject II:3 was diagnosed with ANSD according to the audiological assessments; a ABR, auditory brainstem responses; b ASSR, auditory steady-state response; c DPOAE, distortion product otoacoustic emissions; and d CM, cochlear microphonics

Fig 3

Schematic structure of otoferlin and conservation analysis. a The functional domains of otoferlin and location of the mutations identified in the study. b Conservation of the L1665P of otoferlin. TMD: the transmembrane domain