Genetic Inheritance and Its Contribution to Tinnitus

A Systematic Review on the Genetic Contribution to Tinnitus

PURPOSE

To assess the available evidence to support a genetic contribution and define the role of common and rare variants in tinnitus.

METHODS

After a systematic search and quality assessment, 31 records including 383,063 patients were selected (14 epidemiological studies and 17 genetic association studies). General information on the sample size, age, sex, tinnitus prevalence, severe tinnitus distribution, and sensorineural hearing loss was retrieved. Studies that did not include data on hearing assessment were excluded. Relative frequencies were used for qualitative variables to compare different studies and to obtain average values. Genetic variants and genes were listed and clustered according to their potential role in tinnitus development.

RESULTS

The average prevalence of tinnitus estimated from population-based studies was 26.3% for any tinnitus, and 20% of patients with tinnitus reported it as an annoying symptom. One study has reported population-specific differences in the prevalence of tinnitus, the white ancestry being the population with a higher prevalence. Genome-wide association studies have identified and replicated two common variants in the Chinese population (rs2846071; rs4149577) in the intron of TNFRSF1A, associated with noise-induced tinnitus. Moreover, gene burden analyses in sequencing data from Spanish and Swede patients with severe tinnitus have identified and replicated ANK2, AKAP9, and TSC2 genes.

CONCLUSIONS

The genetic contribution to tinnitus is starting to be revealed and it shows population-specific effects in European and Asian populations. The common allelic variants associated with tinnitus that showed replication are associated with noise-induced tinnitus. Although severe tinnitus has been associated with rare variants with large effect, their role on hearing or hyperacusis has not been established.

Association of Chronic Kidney Disease with Prior Tinnitus: A Case-Control Study

This population-based, case−control study aims to explore the relationship between prior tinnitus and the occurrence of chronic kidney disease (CKD) using a nationwide, population-based cohort study. We used data from the Taiwan National Health Insurance Research Database to explore the association of CKD with tinnitus. We identified 15,314 patients aged ≥40 years old with a first-time diagnosis of CKD as the cases. We used propensity-scored matching to select 45,942 controls (1:3 ratio). We performed multivariate logistic regression to estimate the odds ratio (OR) of a prior tinnitus diagnosis among the CKD group vs. the control group. Analysis showed that 770 (1.26%) out of the 61,256 sampled patients had previously diagnosed tinnitus. Chi-square testing revealed a significant difference in the rate of previously diagnosed tinnitus between cases and controls (3.86% vs. 0.93%, p < 0.001). Univariate logistic regression analysis showed an OR of prior tinnitus for cases of 10.249 (95% confidence interval (CI): (8.662~12.126)) relative to controls. In adjusted analysis, cases were more likely than controls to have a prior diagnosis of tinnitus (OR = 10.970, 95% CI = 9.255~13.004, p < 0.001) after adjusting for age, sex, monthly income, geographic location, urbanization level, hypertension, diabetes, coronary heart disease, hyperlipidemia, obesity, and autoimmune disease. Our study shows that CKD patients have a higher likelihood of having suffered from tinnitus before CKD was diagnosed, but we have no data suggesting that tinnitus is a predictor of subsequent CKD. Patients diagnosed with tinnitus may benefit from proactive measures to prevent CKD and detect it early through lifestyle modifications and regular renal function examinations, regardless of CKD-related symptoms.

The Road Traveled and Journey Ahead for the Genetics and Genomics of Tinnitus

The feasibility to unravel genetic and genomic signatures for disorders affecting the auditory system has accelerated since arriving in the post-genomics era roughly 20 years ago. Newly emerging studies have provided initial landmarks signaling heritability and thus, a genetic link, to severe tinnitus. Tinnitus, the phantom perception of ringing in the ears, is experienced by at least 15% of the adult population and can be extremely disabling. Despite its ubiquity, there is no cure for tinnitus and modalities offering relief are often of limited success. Because tinnitus is frequently reported in patients with acquired conductive or sensorineural hearing impairment, it has been widely accepted that tinnitus is secondary to and a symptom arising from hearing impairment. However, tinnitus has also been identified in the absence of auditory dysfunction and in young individuals, resulting in a debate about its origins. Genetics studies have identified severe tinnitus as a complex disorder arising from gene and environment interactions, refining its classification as a neurological disorder and, in at least a subset of patients, it appears not as a symptom of another health issue. This current opinion summarizes several recent studies that have challenged a long-accepted dogma and postulates how this information could eventually be used in the future to help patients. It is with great hope that this knowledge opens translational paths to provide relief for the many who suffer from the burden of tinnitus on a daily basis.

Too Blind to See the Elephant? Why Neuroscientists Ought to Be Interested in Tinnitus

A curative therapy for tinnitus currently does not exist. One may actually exist but cannot currently be causally linked to tinnitus due to the lack of consistency of concepts about the neural correlate of tinnitus. Depending on predictions, these concepts would require either a suppression or enhancement of brain activity or an increase in inhibition or disinhibition. Although procedures with a potential to silence tinnitus may exist, the lack of rationale for their curative success hampers an optimization of therapeutic protocols. We discuss here six candidate contributors to tinnitus that have been suggested by a variety of scientific experts in the field and that were addressed in a virtual panel discussion at the ARO round table in February 2021. In this discussion, several potential tinnitus contributors were considered: (i) inhibitory circuits, (ii) attention, (iii) stress, (iv) unidentified sub-entities, (v) maladaptive information transmission, and (vi) minor cochlear deafferentation. Finally, (vii) some potential therapeutic approaches were discussed. The results of this discussion is reflected here in view of potential blind spots that may still remain and that have been ignored in most tinnitus literature. We strongly suggest to consider the high impact of connecting the controversial findings to unravel the whole complexity of the tinnitus phenomenon; an essential prerequisite for establishing suitable therapeutic approaches.

Burden of rare variants in synaptic genes in patients with severe tinnitus: An exome based extreme phenotype study

BACKGROUND

tinnitus is a heterogeneous condition associated with audiological and/or mental disorders. Chronic, severe tinnitus is reported in 1% of the population and it shows a relevant heritability, according to twins, adoptees and familial aggregation studies. The genetic contribution to severe tinnitus is unknown since large genomic studies include individuals with self-reported tinnitus and large heterogeneity in the phenotype. The aim of this study was to identify genes for severe tinnitus in patients with extreme phenotype.

METHODS

for this extreme phenotype study, we used three different cohorts with European ancestry (Spanish with Meniere disease (MD), Swedes tinnitus and European generalized epilepsy). In addition, four independent control datasets were also used for comparisons. Whole-exome sequencing was performed for the MD and epilepsy cohorts and whole-genome sequencing was carried out in Swedes with tinnitus.

FINDINGS

we found an enrichment of rare missense variants in 24 synaptic genes in a Spanish cohort, the most significant being PRUNE2, AKAP9, SORBS1, ITGAX, ANK2, KIF20B and TSC2 (p < 2E-04), when they were compared with reference datasets. This burden was replicated for ANK2 gene in a Swedish cohort with 97 tinnitus individuals, and in a subset of 34 Swedish patients with severe tinnitus for ANK2, AKAP9 and TSC2 genes (p < 2E-02). However, these associations were not significant in a third cohort of 701 generalized epilepsy individuals without tinnitus. Gene ontology (GO) and gene-set enrichment analyses revealed several pathways and biological processes involved in severe tinnitus, including membrane trafficking and cytoskeletal protein binding in neurons.

INTERPRETATION

a burden of rare variants in ANK2, AKAP9 and TSC2 is associated with severe tinnitus. ANK2, encodes a cytoskeleton scaffolding protein that coordinates the assembly of several proteins, drives axonal branching and influences connectivity in neurons.