You’ve heard of gene therapy for diseases and cancers. But what about gene therapy for sensory disorders, like deafness? In 2003, scientists discovered that some genes can transform certain ear cells into the hair cells that, when vibrated, generate the electrical activity that awakens your brain to the world of sound. Last year, Hinrich Staecker at the University of Kansas Medical Center and his colleagues inserted one of those genes, Atoh1, into a harmless virus and injected it into the cochlea (a part of the inner ear) of mice. They found that two months later, the mice’s hearing had improved by about 20 decibels— approximately equivalent to the difference between covering and uncovering your ears with your hands.
In the next month, researchers will expose volunteers with severe hearing loss to a new kind of gene therapy first tested in mice. Now Hinrich and his team will test the procedure on humans—specifically, 45 volunteers with severe hearing loss.
Here’s Helen Thomson writing for New Scientist:
The trial will start at the University of Kansas Medical School before being widened to other institutions. As with the mice, the team will inject the viral gene package directly into the volunteers’ cochlea by peeling back their ear drum and passing a needle through a tiny hole made by a laser. The Atoh1 gene should reach the supporting cells, instructing them to divide and form new hair cells. Results are expected between two weeks and two months later.
“Today’s medical treatments are largely limited to hearing aids and cochlear implants, which are essentially just sticking plasters,” says Ralph Holme, head of biomedical research at UK charity Action on Hearing Loss. “This is why the planned trial is extremely encouraging and offers hope to the millions affected by hearing loss that a cure is possible.”
Unfortunately, the procedure wouldn’t help people with congenital deafness because they don’t have the innate ear structures necessary to support the growth of hair cells. But it could still revolutionize the lives of up to 7 million people with acquired hearing loss in the United States alone, giving them access to the very subtle acoustic cues that implants or hearing aids can’t provide.
Jeffrey Holt at Harvard Medical School, who isn’t involved in the trial, calls it ground-breaking and says he is cautiously optimistic about the work. “Hopes are high that the trial will yield positive results without introducing unnecessary complications.”
The only expected side effect is a brief period of dizziness or nausea, a common occurrence after ear surgery. In pre-clinical tests, Novartis researchers looked to see if the virus spread to any other tissues, but found it was restricted to the site of injection. It has also been designed to have limited potential to recombine with the volunteer’s DNA so it is unlikely to cause problems elsewhere.
“Many other species, such as fish and birds, can regenerate the hair cells in their inner ear over time and create new auditory circuits,” says Klickstein. “We’re just trying to tweak the mammalian system a little bit to do what a lot of other species do naturally”.