Around 1 in 200 people in the UK will lose their hearing due to a condition called otosclerosis, which affects the smallest bone in the body, the stirrup (or stapes) bone in the middle ear. In otosclerosis, this bone becomes fixed in place due to overgrowth around the joint of the bone. This means it can no longer move to pass on sound waves to the inner ear – which causes a conductive hearing loss. People with otosclerosis typically begin to lose their hearing as young adults, in their late teens or twenties.
Currently people with otosclerosis either use hearing aids, which are not always effective, or have surgery to remove part of the stirrup bone and replace it with a prosthetic device. This improves hearing in about 80% of people, but it does not restore full normal hearing.
In about a quarter of cases, there is a strong family history of otosclerosis, suggesting that it can be inherited. Recently, the researchers identified the first gene, called SERPINF1, to be linked to otosclerosis. They used a new DNA sequencing technique, called whole exome sequencing, which analyses all the inherited changes present in every gene of affected individuals.
In a related Action on Hearing Loss-funded project, the researchers have been using whole exome sequencing to search for further otosclerosis genes, to find out more about the different processes that can cause otosclerosis, and to investigate how mutations in the genes they identify cause otosclerosis.
As part of this project, they have identified two closely-related genes, which they think are linked to otosclerosis. To confirm if this is the case, they plan to follow up their finding in a much larger group of people. As these genes are very large, the associated sequencing costs to do this are beyond the scope of their original project. They will use the extra funding from this grant to sequence the genes in a large number (around 100) people with otosclerosis, to see if they can identify the same mutations in these genes that they have previously found from studying families with the condition.
Otosclerosis is potentially treatable if the biological process which cause it are understood; this kind of genetic approach will help to reveal them. Identifying genes involved will also improve genetic counselling for affected families and allow early diagnosis where inherited otosclerosis is likely. This is important, as any preventative or restorative drug therapies will be more effective if given before the bone has become fixed in place and hearing loss has developed.