Scientists think injecting gene-carrying viruses could be 'holy grail' for curing deafness

A team of researchers led by Hinrich Staecker at the University of Kansas Medical Center will attempt to cure profound deafness by injecting deaf people with a harmless virus containing a gene that, if all goes according to plan, will trigger the regrowth of sensory receptors in their ears.

Other technologies that treat deafness do so either by amplifying sounds (hearing aids) or translating the sounds into electrical waves that the brain interprets (cochlear implants). Staecker hopes that the gene therapy he and his team have designed will restore "a more natural sense of hearing."

"The holy grail is to give people natural hearing back," he told New Scientist. "That's what we hope to do – we are essentially repairing the ear rather than artificially imitating what it does."

Although much about how the ear works is not fully understood, it is known that sound waves are funneled into the ear, cause the eardrum to vibrate, and that these vibrations are transmitted to the cochlea via three tiny bones. Once inside the cochlea -- in an area known as the organ of Corti -- the tiny hair cells that function as sensory receptors trigger electrical activity in cochlear neurons, and that information is relayed to the brain.

The tiny hair cells are fragile, and can be damaged by, among other things, regular exposure to loud noise and certain antibiotics. Once damaged, they don't regrow. However, in 2005 a team of researchers at the University of Michigan in Ann Arbor discovered that when a harmless virus containing the gene Atoh1 -- which, in embryos, stimulates the development of hair cells -- was smuggled into the cochlea of deaf guinea pigs, they recovered between 50 and 80 percent of their original hearing.

Staecker's team now has permission to run a similar trial on human subjects. Those chosen for the experiment are profoundly deaf -- because as another member of the team noted, Lloyd Klickstein, noted, "the biggest risk is that we interfere with residual hearing, so we're starting with people who have lost almost all hearing already."

Other species, including many fish and birds, can regenerate these hair cells naturally. "We're just trying to tweak the mammalian system a little bit to do what a lot of other species do naturally," Klickstein said.