Otosclerosis is a type of conductive hearing loss that affects adults in their 20s-30s and may lead to profound hearing loss across all frequencies. It is caused by abnormal overgrowth of bone in the middle ear that causes the small hammer bone (stapes) to attach to the ear drum. In some cases, this type of deafness runs in families and is passed on generation after generation. For a diagnosis of otosclerosis, a doctor who is an ears, nose and throat specialist, has to exclude all other diseases that may cause the progressive hearing loss s/he observes in the patient. If the diagnosis is correct, a surgical procedure that separates the hammer bone from the ear drum (known as a stapedectomy) can completely restore hearing. Genetic studies are underway in families with otosclerosis to identify the genes causing the abnormal bone growth in order to understand why it happens so preventative therapies can be developed and to provide a genetic test to identify those who would benefit from the surgical procedure.