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Genes Provide Clues to Hearing Loss

In 1988, when the field of genetics was still relatively new, James Watson, one of the most influential genetics researchers and a co-discoverer of the structure of DNA said: "We used to think that our fate was in our stars, but now we know that, in large measure, our fate is in our genes."

Since then scientists all over the world have been making new discoveries and identifying the relationship between genes and various health problems, including hearing impairments.

One of the newest studies, carried out at Brandeis University, examined the genetic and environmental factors affecting hearing loss, the third most common chronic disability among older adults after arthritis and hypertension.

Deciphering the Genes Mysteries

Dr. Watson was not exaggerating when he emphasized the importance of genetics, the study of the function and behavior of genes.

A gene is a distinct portion of a cells DNA and the basic unit of heredity found in the cells of all living organisms. It determines the physical characteristics that an organism inherits. Human beings have about 25,000 genes.

Not surprisingly, heredity, the process of transmitting biological traits from parent to offspring through genes, plays a significant role in the field of genetics.

To put it simply (although there is nothing simple about it), genetics is the study of heredity. Sometimes, by studying genetics researchers can discover why some illnesses and medical conditions run in families, and search for disease-specific treatments.

For example, in recent studies, scientists discovered that gene therapy might be effective in restoring sight in some people, reverse heart failure, increase the movement control of Parkinsons disease patients, and even suppress a gene that is crucial to HIV infection.

And extensive research suggests that the secrets to hearing loss may be in the genes too.

Genes and Hearing Loss

The connection between genes and hearing impairments has been documented by many studies. Nearly 100 genes are currently known to play a role in hearing loss.

In the last decade, advances in molecular biology and genetics have allowed scientists to glean valuable knowledge into development, function, and pathology of the inner ear. They have identified several of the various genes responsible for hereditary deafness or hearing loss.

For example, European scientists identified a gene called TGBF1, which, they say, is responsible for the single most common cause of hearing loss among white adults, otosclerosis, an abnormal growth of bone in the inner ear.

And researchers from Michigan State University have discovered a set of gene mutations, DFNA 20, which plays an essential role in the structure of the inner ear and leads to progressive hearing loss.

Another gene mutation, the GJB2, is responsible for hereditary deafness, says American Academy of Otolaryngology, Head and Neck Surgery (AAO-HNS).

As one of the most common genetic causes of hearing loss, GJB2-related hearing loss is considered a recessive genetic disorder because the mutations only cause deafness in individuals who inherit two copies of the mutated gene, one from each parent, the AAO-HNS says. A person with one mutated copy and one normal copy is a carrier but is not deaf. Screening tests for the GJB2 gene are available for at risk individuals to help them determine their risk of having a child with hearing problems.

More Evidence

Other research confirms the correlation between genes and hearing. The groundbreaking Brandeis study also bears out the importance of genetic heredity in hearing loss that occurs during late middle age.

The study examined 179 identical and 150 fraternal male twin pairs, ranging in age from 52 to 60. It concluded that about two-thirds of the hearing loss in the individual subjects' better ears could be caused by genetic factors. In their poorer ears, about one-half of the hearing loss was due to genes.

The research suggests that middle-aged and older people with a genetic predisposition to hearing loss should be particularly careful about environmental risk factors such as prolonged and chronic exposure to harmful noise (sounds louder than 85 decibels), as well as medications whose side-effects could be detrimental to hearing. Some antibiotics, anti-inflammatory, blood pressure and chemotherapy drugs, are among the ones that can harm the hearing. Recent evidence also suggests that men taking erectile dysfunction medications may be at increased risk for sudden hearing loss as well.

"This research confirms the importance of genetic factors in age-associated hearing loss, says lead Brandeis researcher Arthur Wingfield, an expert on the relationship between memory performance and hearing loss in older adults. It also confirms the need for vulnerable individuals and their families to take extra care to prevent further hearing damage.

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