Tinnitus in both ears, known as bilateral tinnitus, depends on genetic factors, a twin study conducted by researchers at Karolinska Institutet together with colleagues from the European research network TINNET has found.
Tinnitus prevalence increases with age and is thought to be related to a number of environmental factors but little research has been done on the subject. There are also no effective cures for the condition, due possibly to the heterogeneity of the condition.
“We’ve been able to show that different forms of tinnitus have a significant heritability and thus a dominant genetic influence over environmental factors.”
When the researchers first examined all forms of tinnitus, using data from the Swedish Twin Registry, they made the same conclusions on heritability as others have reported. It was only after grouping the subjects by sex and unilateral/bilateral tinnitus that they uncovered the genetic correlation.
More Pronounced In Men
“This result is surprising and unexpected as it shows that, unlike the conventional view of tinnitus being driven by environmental factors, there is a genetic influence for bilateral tinnitus which is more pronounced in men.”
Their discovery also demonstrates that bilateral and unilateral tinnitus constitute two separate sub-groups, only one of which is influenced by genetic factors. This, claims Dr Cederroth, not only has considerable clinical relevance but is also important from a public health perspective:
“Tinnitus sufferers need better care and treatment than they’re currently getting. We need more genetic studies and a better molecular understanding of its generation, which could open unforeseen avenues to drug development.”
The work was supported by the Swedish Research Council, the Lars Hierta Memorial Foundation, the Magnus Bergvall Foundations, the Silent School Foundation and the Biomedicine and Molecular Biosciences European Cooperation in Science and Technology (COST) Action.
Iris Lianne Maas, Petra Brüggemann, Teresa Requena Navarro, Jan Bulla, Niklas K. Edvall, Jacob v.B. Hjelmborg, Agnieszka J. Szczepek, Barbara Canlon, Birgit Mazurek, Jose A. Lopez-Escamez, Christopher R. Cederroth Genetic susceptibility to bilateral tinnitus in a Swedish twin cohort Genetics in Medicine, doi: 10.1038/GIM.2017.4