Searching for the Molecular Basis of Partial Deafness

Abstract

Hearing is an important human sense for communicating and connecting with others. Partial deafness (PD) is a common hearing problem, in which there is a down-sloping audiogram. In this study, we apply a practical system for classifying PD patients, used for treatment purposes, to distinguish two groups of patients: one with almost normal hearing thresholds at low frequencies (PDT-EC, n = 20), and a second group with poorer thresholds at those same low frequencies (PDT-EAS, n = 20). After performing comprehensive genetic testing with a panel of 237 genes, we found that genetic factors can explain a significant proportion of both PDT-EC and PDT-EAS hearing losses, accounting, respectively, for approx. one-fifth and one-half of all the cases in our cohort. Most of the causative variants were located in dominant and recessive genes previously linked to PD, but more than half of the variants were novel. Among the contributors to PDT-EC we identified OSBPL2 and SYNE4, two relatively new hereditary hearing loss genes with a low publication profile. Our study revealed that, for all PD patients, a postlingual hearing loss more severe in the low-frequency range is associated with a higher detection rate of causative variants. Isolating a genetic cause of PD is important in terms of prognosis, therapeutic effectiveness, and risk of recurrence.

Keywords: PDT-EAS; PDT-EC; cochlear implantation; gene; genetics; hearing loss; high-throughput sequencing; partial deafness; pathogenic variant.

Figure 1

Mean pure-tone audiograms of the analyzed PDT patients. (A) Binaural hearing thresholds in the PDT-EC group; (B) Binaural hearing thresholds in the PDT-EAS group. Solid lines represent the average hearing level and dashed lines represent the maximum and minimum hearing thresholds.

Figure 2

Selected genetic and audiometric data of PDT-EC patients. Families with causative variants in the KCNQ4 gene (A), in the OSBPL2 gene (B), and in the SYNE4 gene (C).

Figure 3

Selected genetic and audiometric data of PDT-EAS patients. Families with causative variants in the ATP2B2 gene (A), in the MYO7A gene (B), in the TMC1 gene (C), and in the USH2A gene (D).