Jackson Lab Scientists Gain Ground in Understanding Most Common Hearing Impairment in Humans

Date: September 2, 2003

Bar Harbor, Maine - Jackson Laboratory Research Scientists Kenneth Johnson, Ph.D., and Qing Yin Zheng, M.D., reveal their latest discoveries in age-related hearing loss (AHL) - a condition affecting over half the human population by age 80 - in the September issue of the international science journal, Nature Genetics. The most common form of human hearing impairment, AHL adversely affects the quality of life of about 30 percent of the elderly population.

In collaboration with Konrad Noben-Trauth, Ph.D., of the National Institute on Deafness and Other Communication Disorders, Drs. Johnson and Zheng study the genetic basis of human AHL using common, inbred mouse strains as research models. Although many genes affecting hearing have been identified by the analysis of mutations that cause profound, early-onset deafness, this paper demonstrates for the first time that rather than a mutation, the progressive AHL of certain inbred mouse strains is caused by a subtle polymorphism (change in form) of a gene called Cdh23.

This "subtle polymorphism" may be responsible for altering the adhesion or shape of the protein involved in the formation of minute hair cells that line the cochlea in the ear. Movement of these hair cells generates the impulses that the auditory nerve carries to the brain. It is the damage or loss of these hair cells over time that causes AHL. The condition typically impairs an individual's ability to hear high frequency sounds. The genetic basis of human AHL is poorly understood due to both genetic and external factors such as noise trauma or disease that complicate basic studies. "The mouse is much more amenable to genetic analysis. Our results in mice suggest that similar genetic polymorphisms may underlie human AHL susceptibility," Dr. Johnson said.

"Further studies are aimed at identifying additional genes that affect AHL susceptibility in mice and then examining their homologs (the same genes in humans) to see if they contribute to AHL in human populations. A better understanding of the genes and molecular mechanisms underlying AHL will contribute to the development of diagnostics, preventive interventions, and therapies."

Noben-Trauth K, Zheng QY, Johnson KR. Association of cadherin 23 with polygenic inheritance and genetic modification of sensorineural hearing loss. 2003. Nature Genetics 35:21-23.

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