'Editing' out faulty gene responsible for hearing loss

Print edition : January 19, 2018

Promising gene-editing technologies can prevent hearing loss in young animals. Photo: Getty Images

In a major feat that could go a long way towards treating hereditary hearing impairments, researchers have, for the first time, found a way to “edit” out the faulty gene that causes progressive hearing loss, using a promising gene-editing technology called CRISPR-Cas9.

It is also called molecular scissors because the enzyme Cas9 has the ability to snip strands of the DNA double helix, which can ultimately disable a gene.

Researchers in the United States, led by David Liu, professor of chemistry and chemical biology at Harvard University, showed that in mice, molecular scissors can disrupt the mutant version of a gene called Tmc1, which is important for the growth of inner ear’s hair cells, which help detect sound. A single spelling error in this gene can trigger progressive hearing loss in humans as well as in mice.

The findings, announced in the prestigious journal Nature on December 20, are clinically significant as genetic factors are responsible for nearly half of all deafness cases.

Liu and his colleagues designed a lipid-encapsulated Cas9–guide RNA complex that can specifically target a deafness-causing genetic mutation in a mouse model of human deafness. A single treatment involving injection of the genome-editing complex can prevent hearing loss in young animals.

One of the challenges encountered by the scientists was directing Cas9 to target only the bad copy of Tmc1, and not the good one. This can be tricky because the two copies differ by just one DNA letter. But the scientists managed to do so by using an RNA guide to lead Cas9 to the mutant copy of the gene.

After eight weeks, hair cells in treated ears resembled those in healthy animals—densely packed and tufted with hairlike bundles.

The scientists are not sure whether it would work in humans. “We hope that the work will one day inform the development of a cure for certain forms of genetic deafness in people,” Liu said.

Compiled by T.V. Jayan