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Age Related Hearing Loss

Background: Age-related hearing loss (AHL) makes the everyday tasks of life difficult for millions of Americans. Unfortunately, determining exactly what causes susceptibility to AHL is not a simple matter of finding one faulty gene. Scientists are discovering that AHL susceptibility is due to defects in several genes. Studying AHL in humans is made even more complicated because it shows up later in life and it is difficult to determine how much hearing loss is due to non-genetic factors, such as noise, drugs that damage the ear, or disease. Scientists often study mice as models for these problems. The inner ears of mice and humans function similarly, and mice can be raised in an environment that is free of noise, disease, or damaging drugs. Moreover, disease-related mouse genes often have disease-related human equivalents.

Advances: Two groups of NIDCD-supported scientists have identified new genetic mutations in mice that play a role in susceptibility to AHL. Scientists at the Jackson Laboratory previously described mutations in a gene called Ahl that causes mice to develop AHL. However,they noted that different strains of mice with the same mutation developed hearing loss at different ages, and concluded that other genes must also play a role in AHL. Now they have described a second gene - called Ahl2 - that seems to be responsible for the differences in when hearing loss begins in the different mouse strains. At NIH, NIDCD intramural scientists have also described mutations in a mouse gene that help determine how much hearing a mouse with the mutation loses as it ages or is exposed to noise. Mice that have two copies of the mutated gene develop AHL, as do mice that inherit one mutated copy in combination with other genes that contribute to AHL.

Implications: The identification of genes that contribute to hearing loss in mice will help scientists identify similar genes in humans. Scientists may then use this information to design genetic diagnostic tests, preventive measures, and treatments for age-related hearing loss.

*Johnson KR, Zheng QY. AHL2 ,a Second Locus Affecting Age-Related Hearing Loss in Mice. Genomics 80:461-64,2002.
Noben-Trauth K, Zheng QY, Johnson KR. Association of Cadherin 23 with Polygenic Inheritance and Genetic Modification of Sensorineural Hearing Loss. Nat Genet 35:21-3,2003.

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