We often take for granted the complex nature of hearing, as we just put on our headphones or turn up the radio in the car and lose ourselves in the rhythm of a good tune. Yet, within our ears and brains, a carefully orchestrated set of events interprets sound waves into something that can evoke emotion, movement, or deep contemplation. For many years, scientists have had a decent understanding of the mechanics behind hearing—at the cell biology level. However, much of molecular symphony-conducting events associated with hearing have been unknown.
Now, a team of investigators from Medical Research Council (MRC) Harwell, U.K., has just published evidence uncovering 52 previously unidentified genes that are critical for hearing. Researchers in the new study—published today in Nature Communications in an article entitled “A Large-Scale Hearing Loss Screen Reveals an Extensive Unexplored Genetic Landscape for Auditory Dysfunction”— screened over 3000 strains of knockout mice for signs of hearing loss. Knockout mice have one gene from their genome inactivated, which helps researchers to uncover the functions of that gene. The International Mouse Phenotyping Consortium (IMPC) aims to generate a knockout mouse for every gene in the mouse genome.
“Importantly, the large number of hearing loss genes identified in this study demonstrates that there are many more genes involved in deafness in mouse and human genomes than we had previously realized,” explained senior study investigator Steve D.M. Brown, Ph.D., director of MRC Harwell. “Our findings identify 52 genes that have previously not been recognized as being critical for hearing. These increase our knowledge of the many genes and molecular mechanisms required for hearing and also provide a shortlist of new genes to investigate to discover the genetic basis of many human hearing loss syndromes. Testing these genes in people with hearing loss may help to improve diagnosis and counseling of patients.”
The hearing thresholds of the knockout mice were assessed with rising volumes of sound at five different frequencies—mice were considered hearing impaired if they could not hear the quieter sounds for two or more frequencies.
The research team identified 67 genes that were associated with hearing loss, of which 52 had not been previously linked with hearing loss. The genes identified varied in how they affected hearing—effects ranged from mild to severe hearing loss or resulted in difficulties at lower or higher frequencies.
The knockout mice tested so far in this study represented only about 15% of mouse genes, so the researchers estimate that if the entire genome is searched there will be at least 450 genes required for hearing function.
“The next steps will be to determine the role that each of the proteins encoded by these genes has within the auditory system,” noted Dr. Brown. “Further investigation of these hearing loss mouse models will increase understanding of how the auditory system develops, is maintained, and the pathological processes involved with its decline. In particular, we need to establish whether the genes impact on known hearing loss pathways or if they implicate new processes in the auditory system. A longer-term benefit that could arise from studying these models might be the identification of critical cellular functions, which can then be targets for therapies.”
In humans, there are over 400 genetic syndromes that include a hearing loss component. However, most of the genes underlying hearing loss syndromes are currently unknown.
“Mouse genetics has played an important role in our understanding of the development and functioning of the mammalian auditory system,” concluded lead study investigator Michael Bowl, Ph.D., a group leader at MRC Harwell. “We anticipate this list of hearing loss genes will grow hugely over the coming years, as the International Mouse Phenotyping Consortium continues to screen new mutants.”