Knowledge

Advances in Gene Therapy and Hearing Loss

Gene therapy has been showing promise with a multitude of medical applications and researchers are learning more with each day.

Is it possible that gene therapy could restore hearing to those with certain types of hearing loss? It just may be, according to a 2015 study at Boston Children’s Hospital and Harvard Medical School conducted on deaf mice.

There are more than 70 different genes that are known to cause deafness when mutated. The study looked at a particular kind of hearing loss caused by genetic mutations in the TMC1 gene. This mutation is thought to cause four to eight percent of inherited hearing loss, and a mutation to two copies of the TMC1 gene causes a profound hearing loss in children by age two.

<h2>How the study was performed</h2>
<p>This double mutation was replicated in the test mice by breeding them without the TMC1 gene at all, causing them to be born completely without hearing. The second set of mice was bred with a specific mutation in the TMC1 gene. In people, this mutation leads to gradual loss of hearing by ages ten to fifteen.</p>
<p>These mice were then treated with gene therapy. The treatment consisted of inserting a healthy TMC1 gene into a non-harmful virus and then injecting that virus into the mice’s inner ears.&nbsp;</p>
<h2>The Results&nbsp;</h2>
<p>The researchers in the TMC1 mouse study were surprised to find that the deaf mice became able to hear after the gene therapy. When placed in a “startle box,” the mice that had previously been unaffected by sharp sounds now startled and jumped as high as mice with regular hearing did when exposed to the sounds.</p>
<p>In addition, the therapy hel<span style="font-size: 17px; letter-spacing: 0px;">ped the hair cells inside the mice’s ears to become able to respond to sound again. Researchers even found that activity in the auditory portion of the mice’s brain stems was restored.</span></p>

How the study was performed

This double mutation was replicated in the test mice by breeding them without the TMC1 gene at all, causing them to be born completely without hearing. The second set of mice was bred with a specific mutation in the TMC1 gene. In people, this mutation leads to gradual loss of hearing by ages ten to fifteen.

These mice were then treated with gene therapy. The treatment consisted of inserting a healthy TMC1 gene into a non-harmful virus and then injecting that virus into the mice’s inner ears. 

The Results 

The researchers in the TMC1 mouse study were surprised to find that the deaf mice became able to hear after the gene therapy. When placed in a “startle box,” the mice that had previously been unaffected by sharp sounds now startled and jumped as high as mice with regular hearing did when exposed to the sounds.

In addition, the therapy helped the hair cells inside the mice’s ears to become able to respond to sound again. Researchers even found that activity in the auditory portion of the mice’s brain stems was restored.

What does this mean for people with hearing loss?

For those with this particular type of hearing loss, as well as other genetically caused hearing loss, this study provides a ray of hope for the future. Ultimately, the research team, under the lead of Harvard professor Jeffery Holt, Ph.D, hopes to start clinical trials of TMC1 gene therapy within 5-10 years. 

“Our gene therapy protocol is not yet ready for clinical trials—we need to tweak it a bit more—but in the not-too-distant future we think it could be developed for therapeutic use in humans," says Holt. "I can envision patients with deafness having their genome sequenced and tailored, precision medicine treatment injected into their ears to restore hearing." 

For now, HearUSA reports that almost all (95 percent) of Americans with hearing loss can be treated with hearing aids. Browse low cost and digital hearing aids here. 

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