Cause Of Early Hearing Loss Linked To A Genetic Mutation Of An Inhibitor

Hearing loss is a problem no matter how or when it strikes someone. Most young people associate hearing loss with the older generation and don’t give it a second thought. There are a great number of things that can cause hearing loss. Injury, noise trauma, medication and plain old wear and tear on the various parts of the ear are all well-documented causes. Thanks to concerts getting louder and the growing popularity of things like iPods and mP3 players, noise-related hearing loss is becoming more common but hearing loss due to age is still the most common.

Previous research has shown that age-related hearing loss presents itself in most adults after the age of 60 but natural wear and tear shouldn’t be an issue for someone in their teens or twenties. As there have been many documented cases of much younger people developing the symptoms of age-related hearing loss, researchers from the department of biochemistry and molecular biology at Monash University and the otolaryngology department at the University of Melbourne have conducted a new study. This study was designed to look at genetic abnormalities in the hope of determining the causes of this early onset of hearing deterioration.

To understand what causes hearing loss, we first need to understand how hearing works. So let’s quickly go through what happens in your ear. When sound enters the ear, it passes through the eardrum into the middle ear and travels into the cochlea. Within the cochlea are tiny hair cells that vibrate and convert the vibrations into electrical signals. These signals are then sent to the brain via the auditory nerve where they are processed as sound.

These hair cells are called Cilia and are an important part of this study. If they are not functioning correctly, the path of the sound is disrupted and
blocked from going any further, meaning the brain receives no signal to turn into sound.

Now this study was built on previous research into mutations in the genes that can cause this type of problem.

In 2010, a genetic mutation was found that caused hearing loss prompting the researchers to begin an investigation of this mutation further. Recent discoveries have shown that this particular mutation causes an inhibitor to malfunction. This inhibitor is scientifically known as SERPINB6 and it has been found that it is necessary to block a certain enzyme created by the body that destroys proteins. Without this inhibitor, the deterioration of hearing is greatly accelerated although the exact reason is still unknown.

The lead author of this study, Dr. Justin Tan of the University of Melbourne said, “individuals who lack both copies of this good gene were reported to lose their hearing from 20 years of age. This is unusual because most people show gradual signs of age-related hearing loss from 60 years of age onwards but mutations in SERPINB6 accelerate this process. It is not yet clear how this mutation causes hearing loss.”

In order to see these results more clearly, they began conducting tests involving this mutation. These tests were carried out on infant mice who were artificially induced with this condition shortly after birth. When the mice reached 3 weeks of age they have tested again and the results showed that they had begun to exhibit signs of hearing loss. In human terms, this would be the equivalent of a teenager developing the condition. Further studies were carried out as the mice aged that showed, just as in humans, the hearing loss continued to increase as time passed. When the mice were examined under a microscope the researchers discovered that the tiny sensory hair cells in the inner ear had actually died.

As I mentioned before, these hair cells are essential for normal hearing as the hairs vibrate when sound enters the ear. These vibrations are turned into electrical impulses which are then sent to the brain and processed as sound. This is not the first time that researchers have seen mutations that affect the sensory hair cells, they have long been aware of this problem and several studies have been carried out. It was the effects that they witnessed in neighboring cells that proved to be the biggest discovery.

This particular mutation had also killed the group of cells known as fibrocytes. Both types of cells are essential for creating the electrical signals that result in a normal hearing. As I already said, the mutations in sensory hair cells have been apparent for decades but mutations in the fibrocytes are still very uncommon.

The researchers are excited about this discovery as the link between the SERPINB6 inhibitor and the cell deterioration has provided further insight into the genetic causes of hearing loss.

After analyzing the results of this study, Dr. Tan was quoted as saying, “This is an exciting discovery for our hearing because the role of SERPINB6 as an inhibitor is now being unraveled”

Of course, scientists are still a long way from finding a cure for deafness or hearing loss but each breakthrough is a step closer. For many people, a life of wearing hearing aids is inevitable due to these genetic mutations and although hearing aids are becoming smaller and more technologically advanced, I’m sure no one would choose to wear them if given the choice.

It is studies like these that are providing hope that perhaps one day if the exact causes can be identified, an early hearing loss could potentially be a thing of the past. At the very least, they may be able to find a way to delay it.

References

  1. http://alumni.news.unimelb.edu.au/hearing-loss-clueuncovered
  2. http://www.medicalnewstoday.com/releases/261904.php
  3. http://www.journals.elsevierhealth.com/