Gene-editing in mice minimizes hearing loss

Scientists are one step closer to using CRISPR-Cas9 to cure some types of hearing loss.

In a paper published this week in Nature, researchers describe how they used the CRISPR-Cas9 complex to alter a faulty gene associated with a form of inherited, progressive hearing loss in the tiny ears of newborn mice.

Eight weeks after receiving the treatment, the mice were able to hear significantly better than their untreated peers.

Specifically, the treated mice could hear at the level of a quiet conversation, while the untreated mice could hear at the level of an old-fashioned garbage disposal.

The authors said that while the new work is promising, much more research needs to be done before they know if the same technique will work in humans.

“Sometimes the mouse model is a good approximation of how the human patient behaves and sometimes not,” said David Liu, a professor in the department of chemistry and chemical biology at Harvard University who led the work.

Still, he said there are reasons to be optimistic. In part, that’s because the same mutation leads to progressive hearing loss in both mice and humans.

Previous studies have shown that genetic factors are responsible for nearly half of all cases of deafness.

In addition, approximately 20 per cent of genes associated with genetic deafness are dominantly inherited. That means that if you get one good copy of the gene from one parent and one bad copy from the other, it’s the bad gene that will prevail.

In this study, the authors worked with a strain of mice known as the Beethoven strain, after the famous composer who suffered progressive hearing loss over the course of his life.

Beethoven mice have a single erroneous letter in a gene called TMC1 that causes the animals to gradually lose their hearing. The genetic defect affects the function of small hair cells in the inner ear that detect acoustic vibrations. As time goes on, most of the hair cells die off in mice — and people — with the genetic mutation. To keep this from happening, the authors set out to use the CRISPR gene editing system to bind to and cut the faulty TMC1 gene, allowing the good copy to become dominant.