Contribution of Mitochondrial Genetic Factors in Individuals with Tinnitus

Abstract

Genetic factors, such as hearing loss, noise exposure, stress, and ototoxic medications, contribute to the onset of tinnitus. It was found that mitochondrial DNA (mtDNA) mutations can impair oxidative phosphorylation, leading to various disorders, including hearing loss and tinnitus. The present study aims to investigate the relation between tinnitus and the genetic factors in three participant groups such as acquired hearing loss with tinnitus (N=40, 35.22 ± 10.33 years), tinnitus without hearing loss (N=40, 41.8 ± 10.77 years), and a control group (N=40, 32.8 ± 7.82 years). All the participants underwent a comprehensive audiological evaluation, including pure tone audiometry, speech audiometry, tympanometry, reflectometry, and oto-acoustic emissions (TEOAE and DPOAE). Only Group 1 and 2 participants underwent the administration of the Tinnitus Handicap Inventory (THI) questionnaire to quantify the severity of their tinnitus. Further, the genetic analysis included the identification of mtDNA mutations using direct sequencing. Results showed that the mtDNA mutations were observed with tinnitus associated with hearing loss, ototoxicity, Leber Hereditary Optic Neuropathy (LHON), and other deaf risk factors. The defects in this mtDNA can disrupt the function of mitochondrial diseases that can cause tinnitus. In the present study, the detected mtDNA variants in individuals with tinnitus were m.827G>A, m.1095T>C, m.1555A>G, m.5558A>G, and m.15930G>A. The exciting finding of the study was that the individuals identified with genetic mutations had severe to catastrophic handicaps as per THI scores. Among these, nine individuals were suffering from tinnitus without any hearing loss, and others ranged from minimal to severe hearing loss. Therefore, the findings of the present study suggest that understanding and associating genetic factors is crucial, and this can help audiologists with genetic counseling and identify several disorders at high risk for tinnitus.