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Another gene linked to deafness

BETHESDA, Md., Aug. 26 (UPI) -- Scientists have discovered another gene that can lead to deafness if it is defective, bringing the total number of genes known to play a role in hearing loss to 26.

Defects in the new gene, called the trans-membrane inner ear expressed gene or TMIE, was found to be associated with deafness or hearing loss in individuals from five families with a history of deafness.

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The normal function of the gene is not yet known, but isolating its role in hearing could lead to treatments for deafness, Richard Smith, a hearing specialist at the University of Iowa who was involved in the research, told United Press International.

David Kohrman, a University of Michigan professor who focuses on deafness research and first discovered the TMIE gene in mice, told UPI the gene appears to play a role in the normal function of sensory hair cells in the ear. These specialized cells convert external sounds to electrical signals in the ear that can be sent to the brain, which interprets the signals as sounds. If the cells are not functioning properly, then we are unable to hear.

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Smith and colleagues at the National Institutes of Health used DNA segments from the mouse gene to look for similar segments in several families with deaf members in India and Pakistan. In total, the researchers identified five mutations in the TMIE gene that cause deafness.

Kohrman said he believes the finding could lead to therapies that could correct some forms of deafness. His lab plans to begin experiments soon to determine if it is feasible to replace the defective TMIE gene with a normal version.

Using gene therapy, the researchers will administer viruses that carry the correct form of the gene to mice. The hope is the viruses will insert the correct copy of TMIE in each test mouse's genome and replace the defective gene. Kohrman said he also plans to begin an experiment to see if the gene is involved in age-related hearing loss. It is possible that TMIE is turned off as we age, which could lead to deafness in our twilight years, he said.

Kohrman's lab also is trying to ascertain the normal role of the gene in mice. Although it appears to help maintain the sensory hair cells, no one yet knows how TMIE is involved in this process, he said, but proper development and maintenance of the hair cells are critical to hearing, and many of the 25 other deafness-associated genes discovered so far ultimately cause hearing loss by disrupting the hair cells, he said.

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One of the difficulties in devising treatments for deafness is that "we're at the very beginning of understanding it at a genetic level," Smith said. He predicted there probably will be more genes identified that play a role in deafness. "The number of deafness-associated genes will easily double" from the 26 already identified, he said.

Mutations in any of these genes can lead to deafness, Smith added, noting all the components of hearing are necessary for the ear to function properly. "It's like the mechanics of a watch," he said. "If you take out any piece ... then the watch won't work."

The findings appear in the September issue of the American Journal of Human Genetics.

(Reported by Steve Mitchell, UPI Medical Correspondent, in Washington)

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