New clues to human deafness found in mice

Providing clues to deafness, researchers at Washington University School of Medicine in St. Louis have identified a gene that is required for proper development of the mouse inner ear.

In humans, this gene, known as FGF20, is located in a portion of the genome that has been associated with inherited deafness in otherwise healthy families.

“When we inactivated FGF20 in mice, we saw they were alive and healthy,” says senior author David M. Ornitz, MD, PhD, the Alumni Endowed Professor of Developmental Biology. “But then we figured out that they had absolutely no ability to hear.”

The results, published online Jan. 3 in PLoS Biology, show that disabling the gene causes a loss of outer hair cells, a special type of sensory cell in the inner ear responsible for amplifying sound. While about two-thirds of the outer hair cells were missing in mice without FGF20, the number of inner hair cells, the cells responsible for transmitting the amplified signals to the brain, appeared normal.

“This is the first evidence that inner and outer hair cells develop independently of one another,” says first author Sung-Ho Huh, PhD, postdoctoral research associate. “This is important because most age-related and noise-induced hearing loss is due to the loss of outer hair cells.”

As such, Ornitz and Huh speculate that FGF20 signaling will be a required step toward the goal of regenerating outer hair cells in mammals, the only vertebrates incapable of such feats of hearing restoration.

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