The researchers evaluated gene therapy in a mouse that had TMC1 completely deleted and in another mouse with a specific TMC1 mutation.
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Scientists from the Swiss Federal Institute of Technology in Lausanne and the Boston Children’s Hospital, tested hearing in newborn mutant mice by seeing how high they jumped when startled by a noise.
The researchers attached healthy copies of the gene to a harmless virus, which was injected into the inner ears of the mice and “infected” hair cells in the ears of the deaf mice.
Genetic defects affecting the sensory hair cells of the inner ear are a major cause of deafness among children.
Pioneer News published comments by one of the study’s leaders, scientist Jeffrey Holt, who reports that seeing the mices” ears begin to respond to sound was “one of those “Eureka!’ moments”.
“These new research findings are encouraging and open the door for gene therapies, providing hope for people with certain types of genetic hearing loss”, says Ralph Holme, of the United Kingdom research charity Action on Hearing Loss.
Mice that had defective genes replaces with working copies showed evidence of a restored ability to sense sound, researchers say.
“We need to tweak it a bit more, but in the not-to-distant future we think it could be developed for therapeutic use in humans”, Dr Holt said. (The force of their jump was measured by a plate on the floor underneath them; it was detectable at sounds beginning around 80 decibels.). Sensory hair cells contain tiny projections called microvilli, each tipped with a channel formed by TMC1 and TMC2 proteins.
A potential obstacle to the development of gene therapy for inherited deafness is funding, said Dr. Tobias Moser, as reported by NPR.
“I can envision patients with deafness having their genomes sequenced and a tailored, precision medicine treatment injected into their ears to restore hearing”, said Holt, adding, “This is a great example of how the basic science can lead to clinical therapies”.
“Current therapies for profound hearing loss like that caused by the recessive form of TMC1 are hearing aids, which often don’t work very well, and cochlear implants”, says Margaret Kenna, MD, MPH, a specialist in genetic hearing loss at Boston Children’s Hospital who is familiar with the work.
“Anything that could stabilise or improve native hearing at an early age is really exciting and would give a huge boost to a child’s ability to learn and use spoken language”, she said. “Cochlear implants are great, but your own hearing is better in terms of range of frequencies, nuance for hearing voices, music and background noise, and figuring out which direction a sound is coming from”.
It might even be possible to treat hereditary deafness and blindness at the same time, says Holt, because some mutations in TMC1 cause both through a condition called Usher Syndrome.
Babies born with severe to profound hearing deficits occur in up to three per 1,000 live births, the statement said. Arriving sound waves wiggle the microvilli, causing the channels to open. The opening of these channels transmits electrical signals from the inner ear to the brain, and mutations that prevent this from working make a person deaf.
The scientists tried this therapy on two different deafness-causing mutations.
“This is something clinicians can do without too much trouble”, Holt said. But when the gene is mutated, he says, this doesn’t happen.
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Jumping mice! Seeing them leap in surprise after a blast of loud noise was how a team of researchers could tell that they had cured these mice of their deafness.
