With gene-editing technology, scientists can remove harmful genes from a person's DNA and replace them with genes that function properly. CC0 Creative Commons

Scientists have used gene editing tools to prevent hearing loss in mice with a genetic disposition to gradually turn deaf later in their life.

An international team of scientists made this breakthrough using CRISPR-Cas9, a gene editing tool that has gained importance in the recent past.

The researchers used a type of mouse known as a Beethoven mouse, which carry a defect that causes them to lose their hearing starting early in life.

The researchers cut out only the copy of a gene that causes the condition without modifying the rest of the DNA. By targeting more cells near inside the ear, the team was able to prevent the mice from going completely deaf.

The international team of researchers used the nuclease Cas9, which cuts DNA at a specific site by using a snippet of RNA that binds to both the enzyme and the target DNA.

The team says that the process could be applied to humans with a similar genetic disorder that leads to deafness. It is known that genetic reasons are one of the major causes of deafness.

-How does CRISPR gene editing work. Video explanation by McGovern Institute for Brain Research at MIT.

The study focused on a mutation in a gene called Tmc1 that leads to deafness in mice.
This mutation causes the hair in the inner ear to fall out; these hair pick up vibrations and form the gateway of the hearing process.

These very delicate hair sit on top of the cochlea, a spiral-shaped organ that vibrates in response to sound waves. Nerve cells pick up the physical motion of the hair and send it to the brain, where it is processed as sound.

In families with a history of deafness caused by the Tmc1 gene, future generations are very susceptible. If a child inherits one copy of the mutated Tmc1 gene they will suffer progressive hearing loss, normally starting in the first decade of life and resulting in profound deafness within 10 to 15 years.

The team hopes that as knowledge of gene editing grows — along with the results of this study to back up claims— doctors could reverse or even prevent deafness in humans too.

“That could be an important step forward,” says bioengineer Charles Gersbach of Duke University in Durham, North Carolina in a study commentary published in Nature.

“The vast majority of papers that you see where they’re using CRISPR to correct a mutation in an animal model, they are using delivery systems that aren’t applicable to treating diseases in humans,” he says. “Delivery is still a challenge.”

“This is a nice extension of previous work,” says Daniel Anderson, a biomedical engineer at the Massachusetts Institute of Technology in Cambridge. "The ability to selectively knock out the mutant form of the gene, despite a difference of just one DNA letter between it and the normal form, highlights the potential of CRISPR–Cas9 gene editing," he noted in the same commentary.

The results were reported Dec. 20 in the journal Nature.