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Gene therapy for hearing loss.

Heard the joke about the older gentleman who--convinced that his wife was losing her hearing--repeatedly asks, "What's for dinner?" Frustrated by her lack of response, he moves closer and closer, each time repeating the question. Finally, he stands just behind her and yells, "Honey, what's for dinner?" She turns around and says, "For the fourth time, vegetable stew!"

We have a good friend whose husband periodically suggests to her that she undergo an audiology test to determine her need for a hearing aid. Subsequent testing of the wife (and her husband) revealed clearly that some tones were not coming through as they should, but overall, neither was yet ready for hearing aids.

A recent article in the scholarly journal Nature Medicine announced auditory hair cell replacement and hearing improvement after using gene therapy in deaf lab animals.

That discovery got our attention. Anyone diagnosed with irreversible hearing loss must be interested in the research.

In the inner ear, specialized sensors called auditory hair cells are vital to the ability to hear. Healthy cells translate sound waves into electrical signals that are then carried to the brain. If hair cells are damaged or missing--as may occur with aging and overstimulation--the connection between sound waves and the brain's auditory processing center is broken, resulting in hearing loss.

In the first-of-its-kind study, scientists at the University of Michigan Medical School discovered that infusing the Atohl gene into the inner ear of deaf guinea pigs triggered the growth of new auditory hair cells as well as other supporting cells, resulting in improved hearing.

"Eight weeks after treatment, we found new auditory hair cells in the Atohl-treated ears of the research animals," reports Dr. Yehoash Raphael, director of the study and an associate professor of otolaryngology at the University of Michigan. "Auditory tests indicated that the generation of new hair cells coincided with restoration of hearing thresholds."

The groundbreaking findings are a major step forward in the search for new ways to treat hearing loss in humans. Dr. Raphael emphasizes, however, that much work remains to be done.

Hearing is likely to be distorted in the animals due to incomplete repairs, he explains, adding that it will be several years before the gene therapy is ready for people.

For years, scientists worldwide have been searching for ways to regenerate functioning hair cells. The UM team credits its success to the advances made by others in gene delivery systems and in understanding the molecular mechanism that controls hair cell development.

Guinea pigs are commonly used in hearing research because their inner ear structure is nearly identical to that of humans. The Atoh1 gene, first discovered in fruit flies and present in all animals (including humans), is usually active only during embryonic development.
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Author:SerVaas, Cory
Publication:Saturday Evening Post
Geographic Code:1USA
Date:Jul 1, 2005
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