This is an exciting area of research. I hope we aren’t far from restoring human hearing with it.

In the summer of 2015, a team at Boston Children’s Hospital and Harvard Medical School reported restoring rudimentary hearing in genetically deaf mice using gene therapy. Now the Boston Children’s research team reports restoring a much higher level of hearing—down to 25 decibels, the equivalent of a whisper—using an improved gene therapy vector developed at Massachusetts Eye and Ear.

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More than 5 percent of the world’s population suffers from profound hearing loss, and about 60 percent of the deafness in infants is caused by gene mutations. That’s why scientists at the Boston Children’s Hospital and Harvard Medical School have spent several years refining a technique to repair one of the common genetic disorders that cause deafness, offering hope to millions. The genetic disorder they repaired is Usher Syndrome.
The disorder stems from an abnormality in a gene called ush1c, which encodes the proteins in the inner-ear hair cells. These hairs convert sound vibration into electrical signals for the brain. In people with Usher Syndrome, that conversion does not happen, leaving them with devastating deafness, loss of balance and sometimes even blindness.

The researchers wanted to see if tackling the syndrome at its root – the abnormal gene – could reverse the damage. For this, they turned to a pioneering approach called adeno-associated viral vector, which uses a harmless virus to deliver new genes. They replaced DNA from a virus with a healthy ushc1 gene from a mouse. That altered virus was multiplied in a petri dish, then injected into the inner ears of deaf mice suffering from Usher Syndrome. After six weeks, the mice had almost perfect hearing and full recovery of sensory hair growth, brain auditory function, balance and sound sensitivity down to a whisper. (High-pitch frequency sensitivity was only partially restored.) …

Biotechnology last February, the Boston team started preparing for human trials. In March, they exposed human outer-ear hair cells in the lab to the same ush1c-carrying virus. After 10 days, the virus penetrated about 83 percent of the targeted cells. Although cell function was not tested, the team’s ability to reach so many cells has brought real hope that this technique might be able to cure not just a human ush1c gene defect but other hearing disorders caused by genetic mutations.

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The investigators caution the approach is years away from use in humans, but gene therapy carries the promise of restoring hearing in people with several forms of both genetic and acquired deafness. Some 30 million Americans suffer from hearing loss, and every year about one in 1,000 babies are born with hearing impairment, according to the Centers for Disease Control and Prevention.

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