Hearing Loss Still Permanent?

More and more gene therapies begin to show promise

Did you hear the one about the mouse that jumped when he heard a loud noise?

The funny thing is that he’d been deaf before he received some new genes.

Hearing Loss & Gene Therapy

Exciting things are happening in gene therapy for hearing loss these days and it’s not just affecting mice any more. Human beings are actually in a clinical trial in Kansas, for a gene-based drug that would help restore damaged inner ear hair cells.

The medical profession has always considered hearing loss to be permanent because, well, it always has been. Once hearing is damaged, the body is not able to restore it without help. Hearing aids and cochlear implants are certainly welcome, but they don’t really get your hearing back to normal.

70 genes involved in some aspect of hearing

If only there were a way to fix the damaged genes that cause babies to be born deaf or to unlock and change the code that keeps your damaged ears from healing themselves! With that in mind, over the last couple of decades genetic research has identified about 70 genes involved in some aspect of hearing.

For example, genes Tmc1 and Tmc2, which account for 4-8 percent of congenital hearing loss, involve something called the “mechanotransduction machinery” of the inner ear. More simply, these genes control the part of the ear that converts sound waves into something the brain can “hear” so to speak. When these genes go wrong, so does the conversion process.

Startled Mice are a Good Thing, But The Cat Might Not Agree

Researchers attached corrected genetic material to a harmless virus and injected it into a group of deaf mice. How did they know if it worked? They CAN do scientific stuff like measure brain activity in the areas related to hearing, but that’s not nearly as dramatic as blasting a loud noise and watching them jump. The startle test also proved beyond a doubt that the mice really can hear. The cat was probably sorry to hear this news. Will the mice retain their hearing? Only time will tell, but maybe researchers could play Adele’s “Rolling in the Deep” and see if they cut some dance moves in rhythm.

Other tests in mice lacking a neurotransmitter showed some progress after receiving corrected Vglut3 within 10 days after birth. While they did recover hearing, the mice had fewer auditory cells than normal, meaning their hearing was probably not fully restored. This one, while good news, will need some more work.trailer movie Power Rangers

Human Trials

So when do these treatments hit the human experience? Thanks to Swiss pharmaceutical giant Novartis and the biotech research firm GenVec, the future is NOW. In the summer of 2014, at the University of Kansas Medical Center, the companies began a clinical test of a drug known as CGF166, which has regrown hair cells in mice. Here’s how that came about.

Way back in 1999 scientists had identified a gene named atonal as the one that switches hair growth on and off—switching it off at birth. They also knew that the switch stays on in birds, which DO regenerate damaged hair cells. Armed with that knowledge they found a way to reprogram the gene in humans. The next challenge involved how to get the updated genes into the inner ear where they were needed. It would require a delivery method that had never been tried before.

Switched On Levi’s, We Mean Genes

In CGF166 the “switched on” version of atonal is attached to an adenovirus that has been rendered unable to produce. Technicians then do a one-off injection of the serum directly into the inner ear, about the size of a pea, surrounded by bone. This single dose is enough to trigger the regrowth process. This a first-time procedure.

If this works in humans as well as it did in mice—restoring hearing without side effects—the future would suddenly be really bright. So many people with occupational hearing loss, such as machine shop employees, emergency responders and others who may have to change jobs after experiencing hearing loss, would now be able to keep their jobs.

Success Breeds Success

All this is just the tip of a huge iceberg. If this trial brings the expected success, it will encourage other genetic researchers to renew their efforts, potentially bringing even more options to the table