In a recent study, researchers from Harvard Medical School and the Swiss Federal Institute of Technology in Lausanne have successfully used gene therapy to correct hereditary hearing loss in mice.
About half of child hearing loss cases are caused by defects in a person’s DNA. This study focused on a gene called TMC1, which accounts for 4-8% of genetic hearing loss cases. This gene helps the brain convert sound waves into electrical signals so that they can be interpreted and “heard.”
If TMC1 is mutated, the brain has trouble with this process and the electrical signals are much weaker. If a child has two mutant copies of TMC1, they will likely have severe hearing loss beginning around the age of two. If they have just one mutant copy, they could become deaf around 10-15 years of age.
Scientists involved in this study injected a virus containing a healthy strain of TMC1 into the inner ears of profoundly deaf mice. After one month, many of the mice showed drastic improvements in their hearing ability. While they wouldn’t have noticed a jackhammer or a loud clap of thunder (volumes of about 115 dB) before, the gene therapy allowed them to be able to hear at volumes typical of a lawn mower (85 dB) and jump as a result of sudden sounds.
It’s important to note that there are over 100 other genes that have been linked to hearing loss and deafness, and that the mice’s hearing ability wasn’t completely restored. Gene therapy also cannot restore noise-induced hearing loss, which occurs as a result of overexposure to dangerously loud volumes.
However, the researchers are hopeful that they might begin similar clinical trials on humans within 5-10 years. First, they want to monitor the mice to make sure that the effects are not merely temporary.
One of the researchers, Dr. Jeffrey Holt, told BBC News, "We're very excited about it, but we're also cautiously optimistic as we don't want to give false hope. It would be premature to say we've found a cure. But in the not-too-distant future it could become a treatment for genetic deafness so it is an important finding."