Otosclerosis is a form of progressive conductive hearing loss, which usually begins in young adulthood. It occurs when a bone in the middle ear called the stapes becomes immobilized or fixed, which prevents it from transmitting sound vibrations from the outside world to the inner ear and brain.
"About 1 percent of Americans have been diagnosed with otosclerosis, but it may affect up to 10 percent of the total population," says Marci Lesperance, M.D., an assistant professor of otolaryngology-head and neck surgery in the U-M Medical School.
In recent research, Lesperance and her colleagues discovered the gene underlying a rare hearing loss syndrome, called autosomal dominant stapes ankylosis, which is easily confused with otosclerosis. People with this condition have the same fixed stapes bones as those with otosclerosis, but their hearing loss is present at birth and doesn't get worse as they grow up. People with the syndrome are often farsighted and have unusually broad thumbs and great toes, as well as other skeletal abnormalities.
Lesperance says the syndrome is caused by a genetic mutation occurring early in embryonic development. Since the mutated gene is dominant over the normal version, a child has a 50:50 chance of being born with the syndrome, if one parent carries the mutation.
Comparing DNA from nine members of one family and three members of another family with closely related symptoms, U-M researchers found similar mutations in a gene called NOG. NOG holds genetic instructions for the production of noggin - an essential protein for normal bone and joint development in humans and all mammals. One family member in the study who did not have the syndrome, spouses of family members, an
Contact: Sally Pobojewski
University of Michigan Health System