Gene discovery offers hope against deafness

Scientists have taken a step towards treating the most common cause of deafness, finding the genetic ‘‘master switch’’ that produces a critical type of soundsensitive cell.

The discovery could lead to a treatment where cells in the ear are genetically ‘‘reprogrammed’’ to reverse age-related hearing loss.

Most deafness linked to ageing or noise is caused by the death of what are known as ‘‘outer hair cells’’, found in the cochlea of the inner ear. These expand and contract in response to the pressure of sound waves.

The vibrations are transmitted to another type of cell – inner ear cells – which convert them to electrical signals, which are then relayed to nerve cells to create the sounds we hear.

Scientists had previously been able to produce artificial hair cells, but had failed to coax them to become the highly specialised inner or outer cells.

In a study published in the journal Nature, researchers say they have tracked down a gene that governs whether one or the other is produced.

‘‘Our finding ... will provide a previously unavailable tool to make an inner or outer hair cell. We have overcome a major hurdle,’’ said Professor Jaime Garcia-Anoveros, of the Northwestern University Feinberg School of Medicine in Chicago, who led the study.

The gene in question is called TBX2. When it is silenced in a hair cell, it produces an outer cell. When it is activated, an inner cell is produced.

Garcia-Anoveros believes that the discovery could pave the way for a new therapy. Two genes would first be activated to turn a non-hair cell into a cochlear hair cell. The TBX2 gene would then be deactivated to produce new outer cells, which are not normally produced after birth.

He stressed that other hurdles still had to be overcome. One is that the inner and outer cells work closely with very specific, and distinct, types of supporting cells.

‘‘We are making progress in figuring this out,’’ he said. ‘‘The other [challenge] is that the newly generated inner or outer cells will need to be reconnected with the brain by the right neurons nerves connecting the cochlea and the brain. We are also advancing on this front.’’