By 2050, the number of people worldwide with some form of mild-to-complete hearing loss is projected to increase to about 2.45 billion. That’s worrying, since age-related hearing impairment is the third highest contributor to global years lived with disability, and has been associated with depression and anxiety.
Now, in a new study published in American Journal of Human Genetics, an international team of researchers has identified 10 new genes linked with hearing loss and also located the part of the ear affected – the stria vascularis.
Their findings cast doubt on the belief that age-related hearing impairment originates mainly from sensory hair cells – sensory cells in the outer ear that amplify sound, and in the inner ear that transform sound-induced vibrations into electrical signals interpreted by the brain.
The researchers instead identify the stria vascularis, which is a part of the cochlea that powers the hair cells’ mechanical-to-electrical signal conversion, as a target for potential treatments to help people experiencing hearing loss.
Synthesising the existing genomic data on hearing loss
To integrate scientists’ understanding of the genetic basis of hearing loss, the team conducted a meta-analysis of data from 17 genome-wide association studies (GWAS) that had previously looked at the genomes of a total of 723,266 people with a clinically diagnosed, or who had self-reported, hearing impairment.
It’s one of the largest meta-analyses conducted in hearing genetics to date and it identified 48 genes associated with hearing loss – including 10 novel variants newly linked to hearing.
These new variants highlight the importance of genes expressed in the cochlear lateral wall (which includes the spiral ligament and stria vascularis) in hearing loss.
To further investigate the role of these organs, the researchers looked at RNA-sequencing data from studies in mouse cochleae and brains, and mapped the common variant genomic results to cells from the stria vascularis – indicating its importance in the mechanism of hearing loss.
“It was hypothesised since the 1970s that the stria vascularis may play a role in hearing loss in humans, but the molecular evidence for this was missing until today,” says co-main author Christopher R. Cederroth, an associate professor at the Karolinska Institute, Sweden.
Co-main author Frances Williams, a professor of genomic epidemiology at King’s College London in the UK, adds: “This study points to genes we could target for screening purposes, drug development and even gene therapy in the future.
“This study provides a solid foundation for ultimately improving therapies against hearing loss.”