In a path-breaking development, US scientists have been able to make deaf mice hear a tiny whisper with a landmark gene therapy. They said restoring near-normal hearing in the animals paved the way for similar treatments for people "in the near future".
According to studies, published in Nature Biotechnology, the therapy corrected errors that led to the sound-sensing hairs in the ear becoming defective. The researchers were able to correct the defect using a synthetic virus.
"It's unprecedented, this is the first time we've seen this level of hearing restoration," said researcher Dr Jeffrey Holt, from Boston Children's Hospital, told BBC.
About half of all forms of deafness were caused by an error in the DNA.
In the experiments conducted at the Boston Children's Hospital and Harvard Medical School, the mice had a genetic disorder called Usher syndrome, which meant there were inaccurate instructions for building microscopic hairs inside the ear.
In healthy ears, sets of outer hair cells magnified sound waves and inner hair cells then converted sounds to electrical signals that were transmitted to the brain.
The hairs normally formed neat V-shaped rows, but in Usher syndrome they are disorganised which left them hearing severely affected.
The researchers developed a synthetic virus that ''infected'' the ear with the correct instructions for building hair cells.
After being treated with the therapy, several of the profoundly deaf animals could hear well enough to respond to whispered sounds.
It also helped improve their sense of balance greatly.
"Now, you can whisper, and they can hear you,"said Dr Gwenaelle Geleoc, from Boston Children's Hospital, who led the research, Mail Online reported.
Nineteen out of 25 mice heard sounds quieter than 80 decibels - about twice the normal volume of a human conversation and few could even hear sounds as soft as 25-30 decibels, demonstrating a normal level of hearing.