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 Separately, a clinical trial backed by Novartis is under way to
help a different group of people who have lost their hearing through
damage or disease.
After missteps in the late 1990s and early 2000s, when safety scares
set back research, gene therapy is enjoying a renaissance, with
positive clinical results recently in conditions ranging from blood
diseases to blindness.
"We are somewhat late in the auditory field but I think we are
getting there now," said Tobias Moser of the University Medical
Center Gottingen, Germany, who was not involved in the new research.
"It's an exciting time for gene therapy in hearing."
A key element in current optimism is the development of better and
safer viral delivery systems for getting corrective genes into the
body. In the case of deafness, this involves injecting a
gene-carrying engineered virus into the inner ear.
 There are currently no approved disease-modifying treatments for
disabling hearing loss, which affects some 360 million people, or 5
percent of the world's population, according to the World Health
Organization. Hearing aids can amplify sounds, while cochlear implants turn sounds
into electrical signals for the brain to decode, but such devices
cannot fully replicate natural hearing.
Much of the hearing loss in older people is noise-induced or
age-related, but at least half of deafness that occurs before a baby
learns to speak is caused by defects in one of more than 70
individual genes.
It is these infants Swiss and U.S. researchers hope to help, after
showing that replacing a mutated gene improved the function of hair
cells of the inner ear and partially restored hearing in deaf mice.
Scientists from the Ecole Polytechnique Federale de Lausanne and the
Boston Children's Hospital, who reported their work in the journal
Science Translational Medicine, tested hearing in newborn mutant
mice by seeing how high they jumped when startled by a noise.
The team focused on a gene called TMC1, which is a common cause of
human genetic deafness, accounting for 4 to 8 percent of cases. But
other forms of hereditary deafness could also be fixed using the
same strategy.
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Jeffrey Holt of Boston Children's said the technique still needed
"tweaking" but he hopes clinical trials will start within five to 10
years.
Work at Novartis is more advanced, with the first patient treated
last October in an early-stage clinical trial that will recruit 45
subjects in the United States, with results due in 2017. (https://clinicaltrials.gov/ct2/show/NCT02132130?term=NCT02132130&rank=1)
The Swiss company's product, acquired in a 2010 deal with GenVec
worth up to $214 million, delivers a gene called Atoh1 that acts as
a master switch for turning on the growth of inner ear hair cells
that are central to hearing.
Novartis research head Mark Fishman describes it as a "spare parts"
approach to fixing ageing-related frailty.
The process offers hope to adults whose hair cells have been damaged
by excessive noise, disease or exposure to certain drugs, including
some antibiotics. But it will not help the one to three babies per
1,000 born with severe genetic hearing loss in both ears.
"There are a big range of deafness types needing different
approaches," said Moser.
(Editing by Keith Weir)
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