What's the problem?

Aging nation faces growing hearing loss

SAN FRANCISCO, California (AP) -- An aging U.S. population faces a looming crisis in hearing loss, researchers said Saturday. Some research holds promise, but much is in the early stages.

By 2050, there could be as many as 50 million people in the United States with impaired hearing, Steven Greenberg of Silicon Speech in Santa Venetia, Calif., told the annual meeting of the American Association for the Advancement of Science.

Hearing loss results in social and psychological isolation, "which makes their life hell," Greenberg said.

Thanks to loud music and a generally noisy environment, young people have a rate of impaired hearing 2 1/2 times that of their parents and grandparents, he said.

Stefan Heller of Stanford University said research in restoring damaged hearing cells "is very much at the beginning and it's still a long, long road."

Inner and outer hair cells in the ear pick up sound vibrations and send them to the brain. Damage to outer cells causes hearing impairment which can be helped by hearing aides, he said. Damage to the inner cells cannot be repaired and causes deafness.

Heller said ear stem cells have been isolated in laboratory work and grown into cells that resembled hair cells.

"They're not perfect," he said. When placed in the ear of chicken embryos, most of the cells died. A few survived and were implanted into the inner ear. The next step, he said, is to try the experiment in mice.

Gene therapy is being tested in an effort to produce more hair cells in the ear. The result so far has been a type of hybrid cells and researchers are unsure whether they can get these cells to survive.

Heller said scientists in Japan are experimenting with drugs that seem to help spur the growth of hearing cells in young mice. The results in older mice are far less promising.

There seems to be something not yet understood that prevents new cell development in the inner ear. This is an area where cancer is not known to occur, he said, and an indication that something prevents cell development.