LOS ANGELES, Calif. - Dec. 2, 2008 - Presbycusis, or age-related hearing loss, accounts for 30 percent of all hearing loss. So, why do some people lose their hearing as they get older but other people can still hear a pin drop?
The answer may be in a study released online in the journal Human Molecular Genetics. Advance access is available online at http://hmg.
"This is the first ever and largest genome-wide association study for age-related hearing loss," said Rick Friedman, M.D., Ph.D., lead author and House Ear Institute principal investigator and surgeon at the House Clinic.
The study was conducted in collaboration with colleagues at the Phoenix-based Translational Genomics Research Institute (TGen), Affymetrix in Santa Clara, Calif., and the University of Antwerp, Belgium. It uncovered several genes, but one gene stands out and is believed to put people at risk for hearing loss as they age.
They discovered a common variant in the GRM7 gene, which the research team believes may be associated with susceptibility to glutamate excitotoxicity and hearing loss.
It is the overexpression of glutamate that causes damage to the inner and outer hair cells in the inner ear leading to age-related hearing loss.
"Finding the genetic causes of age-related hearing loss could lead to treatments that would bring relief to millions of people worldwide who now suffer from social isolation, depression and even cognitive impairment as a result of not being able to properly understand what others are saying,'' said Dr. Matthew Huentelman, an investigator in TGen's Neurogenomics Division and one of the lead authors.
Researchers believe this paper's findings represent important and significant progress in the efforts to discover the origins of presbycusis.
"We have known for a long time that genes play an important role in presbycusis, but until now genetic research has lagged behind compared to other important diseases," said Guy Van Camp, director of the Hereditary Deafness Laboratory and professor, University of Antwerp, Belgium. "The identification of GRM7 is a very exciting result, as it may provide insights in the development of the disease."
The study participants were Caucasian, ages 53 to 67, and the samples were collected at eight centers in six nations throughout Europe from population registries or audiological consultations. The team of investigators analyzed the samples and identified genetic risks.
In the lab, the research team used Affymetrix GeneChip® Human Mapping 500K to score markers across the entire genome of more than 2,000 samples.
Friedman said the next step is developing a laboratory model to test pharmaceuticals for possible treatment of presbycusis in the future.
About House Ear Institute
The House Ear Institute (HEI) is a non-profit 501(c)(3) organization dedicated to advancing hearing science through research and education to improve quality of life. HEI scientists investigate the cellular and molecular causes of hearing loss and related auditory disorders as well as neurological processes pertaining to the human auditory system and the brain. Our researchers also explore technology advancements to improve auditory implants, hearing aids, diagnostic techniques and rehabilitation tools. The Institute shares its knowledge with the scientific and medical communities as well as the general public through its education and outreach programs. For more information about HEI please call (800) 388-8612 or visit www.hei.org.
House Ear Institute
The Translational Genomics Research Institute (TGen) is a non-profit organization dedicated to conducting groundbreaking research with life changing results. Research at TGen is focused on helping patients with diseases such as cancer, neurological disorders and diabetes. TGen is on the cutting edge of translational research where investigators are able to unravel the genetic components of common and complex diseases. Working with collaborators in the scientific and medical communities, TGen believes it can make a substantial contribution to the efficiency and effectiveness of the translational process. For more information, visit: www.tgen.org.
TGen Senior Science Writer
About the Hereditary Deafness Laboratory, University of Antwerp, Belgium
This research group, headed by Prof. Guy Van Camp, has localized and identified many genes for different forms of hereditary deafness over the last 15 years. Most of this work was based on purely genetic forms of deafness. Over the last couple of years, this laboratory has started with the analysis of complex forms of hearing impairment such as presbycusis and noise-induced hearing impairment. These types of hearing impairment are caused by a complex interplay between environmental factors, such as noise or exposure to toxic substances or medication, and genes that make people susceptible. The laboratory has collected large numbers of samples, and has developed new methodologies for the analysis of these diseases.