MONDAY, Feb. 14, 2005 (HealthDayNews) -- For the first time, researchers have used gene therapy to grow new auditory hair cells that enabled deaf animals to hear.

Many types of permanent hearing loss are due to damage to sensory hair cells in the inner ear. If this gene therapy is successful in additional studies, it may one day help restore significant hearing loss in humans, the researchers suggest.

"New hair cells can be regenerated in animals that are deaf and have no hair cells," said lead researcher Yehoash Raphael, an associate professor of otolaryngology at the University of Michigan, whose research involved guinea pigs. "After treatment, the animal's hearing is significantly restored."

In their study, the researchers implanted a gene called Atoh1, also called Math1, into the animals' ears. "This gene, during embryonic development, signals for the development of hair cells," Raphael said. "The hope was that if we expressed this gene in the ear, they would become hair cells."

The researchers implanted a modified virus containing the gene directly into the inner ear of the animals in the spot where hair cells should normally be. This gene induced new hair cells to grow where none were present before.

Once the gene was implanted, it took about eight weeks for the guinea pigs to be able to hear. After about four weeks, the hair cells started to appear, Raphael said. "After about two months, they [the cells] look happy and contribute to the functional recovery of hearing," he added.

Raphael hopes that, in the not-too-distant future, the researchers can develop a way to implant this gene into humans. "At this stage, there is a lot more that needs to be done in animals," he said.

The finding appears in the March issue of Nature Medicine.

David P. Corey, a professor of neurobiology at Harvard Medical School, said he was "impressed" by the new research. "People had shown that Math1 could force cells to become hair cells, but this is the first time it has been shown that it can actually restore hearing in an animal. And that is quite significant."

Age-related hearing loss is a huge problem and is mostly caused by the death of hair cells, Corey said. "If we can replace even some hair cells, that could have a really big public health benefit," he added.

Hearing loss is one of the most common conditions affecting older adults. One in three people older than 60, and half of those older than 85, have hearing loss. Causes of hearing loss can include exposure to loud or harmful sounds, as well as a virus or bacteria, heart conditions or stroke, head injuries, tumors and certain medicines, according to the National Institute on Deafness and Other Communication Disorders.

"This is a very important study, which showed that in deaf guinea pigs it is possible to restore some degree of hearing by expressing a gene that is key to the hair cell development," said Zheng-Yi Chen, an assistant professor of neurology at Massachusetts General Hospital and Harvard Medical School. "The current study is a major step forward that shows the new hair cells can help with functional recovery from deafness."

Chen believes this discovery will open the way to new treatments for deafness. "Because of the striking similarity between human and rodent inner ears, there is a strong reason to believe that a similar approach may result in certain hearing recovery in profoundly deaf people," he said.

More information

The National Institute on Deafness and Other Communication Disorders has more on hearing loss.

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