Genetics May Explain Much Age-Related Hearing Loss

February 17, 1998

ST. PETERSBURG, FLA. -- Age-related hearing loss may be lessened or prevented in the future by regulating an enzyme that neutralizes free-oxygen radicals, destructive molecules that can destroy sensory hair cells of the inner ear, suggests preliminary research conducted in the University at Buffalo's Center for Hearing and Deafness.

Using mice lacking one or both components of the genes responsible for production of the antioxidant enzyme superoxide dismutase, or SOD, the UB researchers showed that age-related hearing loss was greater and progressed faster in mice deficient in the enzyme than in mice with a normal genetic makeup and SOD production that served as a control group.

Results of the research were presented here today (Tuesday, Feb. 17) at the annual meeting of the Association for Research in Otolaryngology.

"Before this present study, we thought that hearing loss was a normal process of aging," said Richard Salvi, Ph.D., co-director of the Center for Hearing and Deafness and leader of the research group.

"Then we found people with no loss, and we figured it was related to a low-noise environment. Now we believe that at least some age-related hearing loss is due to a genetic deficiency in antioxidant enzymes, such as SOD. If we are able to regulate the enzyme and modulate the number of free radicals present, there is hope for a therapy for age-related hearing loss. "

To arrive at their findings, the researchers used mice in which one or both components of the gene responsible for production of SOD had been eliminated, along with mice with a normal amount of SOD.

"Mice are good models for studying human hearing loss," said Sandra McFadden, Ph.D., a researcher in the study group, "because like humans, they lose hearing at high frequencies first, while hearing loss in most other animals begins in the lower frequencies."

In one study, the researchers measured auditory sensory-cell loss in mice that were young (2 months), middle-aged (7 months) and aged (17 months). None were subjected to any interventions, such as noise exposure, that could cause cell damage, yet researchers found dramatic differences among the groups

"The control-group mice had some sensory-cell loss just from being old, but far less than the mice lacking SOD," said Robert Burkhard, Ph.D., a principal researcher on the study. "This suggests that SOD may play a role in cell loss, a condition that leads to hearing loss. People who have deficiencies in SOD or other antioxidant enzymes may be at greater risk for losing their hearing."

In a companion study, researchers lead by McFadden measured actual hearing loss, as well as sensory-cell loss, in mice that were 13-months-old, an age roughly equivalent to 50-60 human years. As in the previous study, none of the mice had been exposed to interventions that could affect hearing.

Mice lacking one component of the SOD gene had greater hearing loss than the control-group mice, particularly at the higher frequencies, results showed. The mice lacking both genes were very likely to be deaf at 13 months.

"We know that the free radicals produced throughout the body as by-products of normal cell metabolism can cause extensive damage to living tissues, including the sensory hair cells in the inner ear, if they are not neutralized by antioxidant enzymes," McFadden said. "We think that SOD deficiencies may increase cochlear vulnerability to environmental insults, such as noise or drugs, as well as to injury from normal free-radical activity during aging.

"An increase in antioxidant enzymes that neutralize free radicals, such as SOD, may protect the cochlea from these insults and prevent or lessen hearing loss."

McFadden has received a grant from the National Organization for Hearing Research to study the relationship between noise and aging in the production of hearing loss in SOD-deficient mice.

Other contributors to the study were Dalian Ding, UB research support specialist, and Cephalon Inc., of West Chester Pa., developer of the SOD-deficient mice.

The studies were funded by the National Institutes of Health.

University at Buffalo

Related Hearing Loss Articles from Brightsurf:

Proof-of-concept for a new ultra-low-cost hearing aid for age-related hearing loss
A new ultra-affordable and accessible hearing aid made from open-source electronics could soon be available worldwide, according to a study published September 23, 2020 in the open-access journal PLOS ONE by Soham Sinha from the Georgia Institute of Technology, Georgia, US, and colleagues.

Ultra-low-cost hearing aid could address age-related hearing loss worldwide
Using a device that could be built with a dollar's worth of open-source parts and a 3D-printed case, researchers want to help the hundreds of millions of older people worldwide who can't afford existing hearing aids to address their age-related hearing loss.

Understanding the link between hearing loss and dementia
Scientists have developed a new theory as to how hearing loss may cause dementia and believe that tackling this sensory impairment early may help to prevent the disease.

Study uncovers hair cell loss as underlying cause of age-related hearing loss
In a study of human ear tissues, scientists have demonstrated that age-related hearing loss is mainly caused by damage to hair cells.

Hair cell loss causes age-related hearing loss
Age-related hearing loss has more to do with the death of hair cells than the cellular battery powering them wearing out, according to new research in JNeurosci.

How hearing loss in old age affects the brain
If your hearing deteriorates in old age, the risk of dementia and cognitive decline increases.

Examining associations between hearing loss, balance
About 3,800 adults 40 and older in South Korea participating in a national health survey were included in this analysis that examined associations between hearing loss and a test of their ability to retain balance.

Veterinarians: Dogs, too, can experience hearing loss
Just like humans, dogs are sometimes born with impaired hearing or experience hearing loss as a result of disease, inflammation, aging or exposure to noise.

Victorian child hearing-loss databank to go global
A unique databank that profiles children with hearing loss will help researchers globally understand why some children adapt and thrive, while others struggle.

Hearing loss, dementia risk in population of Taiwan
A population-based study using data from the National Health Insurance Research Database of Taiwan suggests hearing loss is associated with risk of dementia.

Read More: Hearing Loss News and Hearing Loss Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to