| Print | EmailAge Related Hearing Loss |
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| Tuesday, April 01, 2008 |
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 By Susan Lytle, Au.D., CCC-A
One question often asked in audiology clinics is, “Is this hearing loss due to my age?” It is a simple question with a very complex answer. It is estimated that 50% of people have developed a hearing loss severe enough to impair communication by the time they reach 80 years of age. A quick glance at this statistic would make the aging process the culprit for hearing loss. However, one must think about the 50% of persons who do not have a significant hearing loss at age 80. The question that remains is what causes some to be susceptible to changes in hearing as they age while others remain relatively unaffected.
In the 1960s, a few pilot studies were done to see if a comparable rate of hearing loss was noted among the elderly members of tribal communities that lived in relatively quiet surroundings. The general results from these studies showed much less hearing loss with age in the tribal groups when compared to the American and European groups. The assumption from these studies was that environmental noise is a contributing factor to age-related hearing loss. More recent animal studies have led scientists to believe that significant noise exposure in the younger years of life can predispose people to develop hearing loss as they age. Other environmental factors believed to increase the risk for hearing loss with age include exposure to ototoxic medications (certain aminoglycosides and chemotherapy agents), radiation, long-term exposure to certain chemical solvents, nutritional intake and heavy smoking and alcohol use. The effect that these environmental factors have on the ears may be closely tied to genetic factors (Van Eyken et al., 2007).
There is growing literature suggesting that mitochondrial DNA plays a large role in age-related hearing loss. To briefly review basic biology, mitochondria are considered the “power plants” of the cell, transforming organic compounds into energy that easily is accessible to the cell. Mitochondria contain their own DNA, which is distinct from the DNA found in the nucleus of the cell. Mitochondrial DNA is inherited from the mother and is much more susceptible to mutations than nuclear DNA due to its limited ability to repair itself. Mutations in mitochondrial DNA can be inherited or acquired.
Environmental factors such as those discussed above can contribute to mutations in mitochondrial DNA. Mutated DNA accumulates over time and leads to a breakdown in mitochondrial function, which increases with age. Because the inner ear requires a high level of energy to function properly, disruption of the mitochondrial function can lead to damage to the inner ear structures. Hearing loss associated with mitochondrial DNA mutations always is sensorineural (or what some doctors refer to as “nerve loss”), usually gets worse with time, generally effects both ears equally and is worse in the higher pitches than in the lower pitches. This is a text book description of what presents in the clinic as “Presbycusis,” or age related hearing loss (Kokotas et al., 2007).
It is a complex interaction between genetic factors and environmental factors, along with the general wear and tear of the auditory system that contributes to age-related hearing loss. Scientists are excited about the prospects of gene therapy and stem cell implantation in offering rejuvenation to impaired ears. However, the only solution available now for persons with presbycusis is hearing aids. Fortunately, the technology in these devices is developing at warp speed, constantly offering innovations that enhance sound quality and allow better interaction between the hearing devices and complex sound environments.
If you or someone you love struggles with a hearing loss, don’t blame it all on age. As with everything in life, it just isn’t that simple.
Read “Do I Have a Hearing Loss?” or visit the Audiology Department.
About the Author
Susan Lytle, Au.D., CCC-A, works at the Balance and Hearing Center at UT Medical Center. She may be reached at 865.305.6630.
Resources
Van Eyken E, Van Camp G, Van Laer L(2007) “The complexity of age-related hearing impairment: Contributing environmental and genetic factors” Audiology and Neurotology, 12: 345-358.
Kokotas H, Petersen MB, Willems PJ (2007) “Mitochondrial deafness” Clinical Genetics, 71: 379-391.
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