Gene therapy may boost hearing, study finds

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WASHINGTON Australian researchers are trying a novel way to boost the power of cochlear implants: They beamed gene therapy into the ears of deaf animals and found the combination improved hearing. The approach reported Wednesday isnt ready for human testing, but its part of growing research into ways to let users of cochlear implants experience richer, more normal sound.

Normally, microscopic hair cells in the cochlea detect vibrations and convert them to electrical impulses that the brain recognizes as sound. Hearing loss typically occurs as those hair cells are lost, whether from aging, exposure to loud noises or other factors.

Cochlear implants substitute for the missing hair cells, sending electrical impulses to directly activate auditory nerves in the brain. Theyve been implanted in more than 300,000 people but, while highly successful, they dont restore hearing to normal, missing out on musical tone, for instance.

The idea behind the project was a closer connection between the implant and the auditory nerves, whose bush-like endings can regrow if exposed to nerve-nourishing proteins called neurotrophins, usually provided by the hair cells.

Researchers at Australias University of New South Wales figured out how to deliver one of those growth factors. They injected a growth factor-producing gene into the ears of deaf guinea pigs, animals commonly used as a model for human hearing. Then they adapted an electrode from a cochlear implant to beam in stronger-than-normal electrical pulses. That made the membranes of nearby cells temporarily permeable, so the gene could slip inside. Those cells began producing the growth factor, which in turn stimulated regrowth of the nerve fibers closing some of the space between the nerves and the cochlear implant, the team reported in the journal Science Translational Medicine. The animals still needed a cochlear implant to detect sound but those given the gene therapy had twice the improvement, they concluded. Senior author Gary Housley estimated small studies in people could begin in two or three years.

Thats a really clever way of delivering the nerve booster, said Stanford University otolaryngology professor Stefan Heller, who wasnt involved with the Australian work. But Heller cautioned that its an early first step and its not clear how long the extra improvement would last or if it really would spur richer sound. He said other groups are exploring such approaches as drug coatings for implants; Hellers own research aims to regrow hair cells.

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Gene therapy may boost hearing, study finds