Case study suggesting mtDNA mutation as a tinnitus factor: ND1:m.3394T>C
Reviewed by Nathan Barlow

Konadath et al report a genetic case study of a 24-year-old female experiencing reduced hearing sensitivity and tinnitus along with a blocked sensation in her right ear, sudden onset one year prior with no other otological complaints. Standard audiometry along with HF thresholds to 14 kHZ were found to be within 15 dB HL (standard frequency range) and within 20 dB HL for the HF audiometry range (WNL). Tympanometry presented bilaterally with Type A (typical immittance). Reflexes (contra and ipsi) were within normal levels, with tone decay and reflex decay indicating no significant adaptation. TEOAEs using 85 dBL SPL showed typical outer hair cell function and ABR using 90 dBnHL click at 11.1/sec and 90.1/sec showed typical I, III and V peaks and latencies. Additionally LLR (70 dbnHL) responses had no abnormalities present. However, their client’s THI scores were assessed at 80 in the ‘catastrophic’ category on the Tinnitus Handicap Inventor, and were matched at 125 Hz narrowband noise at 20 dB SL. Konadath et al’s main findings expand into DNA analysis of mitochondrial DNA (mtDNA), where they report a mutation in m.3394T>C substitution in ND1 gene of mitochondria. This mutation, the authors report, has been linked to Leber’s Hereditary Optic Neuropathy (LHON) which, along with visual symptoms, can cause auditory dysfunction such as tinnitus and / or vestibular issues. The authors explain this specific mitochondrial mutation has been shown to result in cellular damage at a metabolic level, which then influences physiological changes in both the inner ear and the auditory pathways of the central auditory system. Overall, it is suggested that this mutation may serve not only as a marker for identifying individuals at risk for LHON , but will also provide a plausible mechanism for physiological tinnitus manifestations as well as possibly indicating a predisposition to hearing loss or other hearing disorders. They conclude with a recognition that further research into mitochondrial mutations in individuals with tinnitus would be necessary. Overall, this seems an interesting case study given recent clinical breakthroughs in gene therapy happening in ENT and audiology spaces earlier in 2024, and a developing area to keep an eye on for those involved in assessment and treatment of people experiencing chronic or persistent tinnitus without or with milder hearing difficulties.

Is Mitochondrial Mutation a Predisposing Factor for Tinnitus? A Single Case Study.
Konadath S, Dwarakanath VM, Sylvester C, Yohannan A.
HEAR J
2024;77(11):1–3.