Two to three out of every 1,000 children born in the United States have a diminished level of hearing or can’t hear at all. Around half of these children are born this way because of genes they inherit from their parents. Although hearing loss can be treated with hearing aids and cochlear implants, these technologies don’t correct an underlying genetic problem.
The researchers tested their base editing technique on deaf mice bred to have the TMC1 mutation, converting a C-G base pair into a T-A pair, which corrected the error… Only a quarter of the cells in the mice’s ears ended up getting edited (scientists haven’t yet figured out how to edit 100% of cells yet), but that was enough to restore some amount of hearing. A single injection of the editing treatment reversed abnormalities in inner ear hair cells, which are vital for hearing.
To test whether the treatment worked, the researchers clapped their hands next to the mice. The previously deaf mice that got the treatment jumped, turning to look at the source of the sound. More formal tests involved attaching electrodes below the mouse’s ears and measuring their brain wave activity in response to different sound levels. The mice that received the treatment could hear sounds as quiet as 60 decibels — the level of a normal conversation.