A gene responsible for the single most common cause of hearing loss among white adults has been identified.
The condition is caused by abnormal bone growth
Belgian researchers hope their discovery will lead to new treatments for otosclerosis, which affects approximately one in 250 people.
The condition is caused by abnormal growth of a bone in the middle ear, which interrupts sound waves passing to the inner ear.
Details were announced to a European Society of Human Genetics conference.
It is thought that otosclerosis is caused by a combination of genetic and environmental factors.
Usually starts when people are still in their 20s or 30s
Hearing loss may appear very gradually
Many people first notice that they cannot hear low-pitched sounds or that they can no longer hear a whisper
Other symptoms can include: dizziness, balance problems, or tinnitus
Lead researcher Melissa Thys, from the University of Antwerp, said: "This may be a lead for better forms of treatment in the future; currently the best option is an operation.
"However, there is often an additional component of hearing loss which can't be restored by surgery."
The Antwerp team focused on a gene called TGBF1, which was already known to play a role during the embryonic development of the ear, and to be active in the otosclerotic bone.
They used a technique - SNP (single nucleotide polymorphism) analysis - to search for tiny variations in genetic make-up, and found patients from Belgium and the Netherlands with otosclerosis often had a specific variant in the TGBF1 gene.
Similar results were found in a second analysis, this time of French patients.
Ms Thys said: "Combining the data from both groups gave a very significant result, from which we were able to conclude that we were the first to identify a gene that influences the susceptibility for otosclerosis.
"And, as further evidence, we were also able to show that a more active variant of this gene is protective against the disease."
Dr Catriona Crombie, of the charity RNID, said: "The discovery of the gene responsible for a common cause of hearing loss is a fantastic breakthrough for everyone working to improve the lives of deaf and hard of hearing people.
"The effects of otosclerosis can be devastating - imagine the frustration of incessant ringing in your ears, or of being constantly asked to 'speak up'.
"Researchers can now focus their efforts on this gene and the processes it controls to develop new ways of preventing and treating otosclerosis."
Vivienne Michael, chief executive of Deafness Research UK, agreed the research was significant.
She said: "At the moment the most common treatment is surgery but this finding opens the door to alternative therapies which would prevent or slow the abnormal bone growth that causes the condition."