Gene therapy finds a way to restore hearing

‘‘A lot of the techniques would fairly easily translate into a clinical setting’’ for use in humans, said Matthew Kelley, a neuroscientist with the National Institute on Deafness and Other Communication Disorders.Humans have about 16,000 hair cells in the cochlea of each ear, which convert sound waves into nerve impulses. Once damaged, they cannot regenerate on their own. The key to the generation of new hair cells is a gene called Atoh1, first discovered in fruit flies in 1998 by Huda Y. Zoghbi of the Baylor College of Medicine.

Variants of the gene have since been discovered in almost all species of animals.Researchers showed that the gene could convert supporting cells into hair cells.

Two years ago, Yehoash Raphael and Kohei Kawamoto of the University of Michigan Medical School reported inserting the gene into supporting cells in live guinea pigs produced thousands of new hair cells.

This time, the animals were deafened using toxic chemicals to kill the hair cells in both ears. On the fourth day, they used gene therapy with a viral vector to insert the Atoh1 gene into the guinea pigs’ left ears. Within two months, new hair cells had appeared in the treated ears, but not in the untreated right ears.

The team used tests of auditory brainstem response to measure the guinea pigs’ ability to hear sounds. In effect, they observed increases in brain activity when they exposed the animals to noises.