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 Now aged 56, two years after his retina was
deliberately infected with a virus carrying a gene to correct a
protein deficiency that was destroying its cells, he is a regular on
the tennis court and has a successful career in law.
"For the last 30 years I've been living under the insidious
inevitability of going blind," Stroh told reporters at a briefing
about his experimental treatment. "Now there is a very real prospect
I will continue to be able to see."
Stroh is one of a handful of patients with an inherited cause of
progressive blindness called choroideremia who took part in an early
stage trial of a potential gene therapy treatment designed to
correct a genetic defect that means retina cells gradually die.
Although the results are from only six patients in a very early
stage Phase I trial, researchers said they suggest more studies
should be done to see if similar gene therapies could be developed
for other more common genetic causes of blindness such as macular
degeneration and retinitis pigmentosa.
Choroideremia is caused by a mutation in a gene that makes a protein
called REP1. It affects an estimated 1 in 50,000 people and causes
sufferers — mainly men — to lose their sight gradually as the cells
in the retina degenerate.
DELIVERING DNA
There is currently no licensed treatment for the condition and
eventually the photoreceptor cells — the rods and cones in the
retina that respond to light by sending signals to the brain — die
completely, leading to blindness by middle age.
In the trial, a team led by Robert MacLaren of the University of
Oxford, a consultant surgeon at the Oxford Eye Hospital, injected
the patients' retinas with a vector — in this case a genetically
engineered virus — to deliver a corrective copy of the gene to the
appropriate part of the eye.
"The virus has to be delivered to the target cells, which are the
cells of the retina," MacLaren explained. To do that, the surgeon
performs an operation similar to cataract surgery in which the
patient's retina is detached and lifted, and the virus is then
injected underneath with a fine needle.
"The virus goes in, infects the cells and puts the protein back into
the cells — so we're harnessing the capability of the virus to
infect cells and deliver its DNA," he said.
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"This is the exciting thing about gene therapy," said MacLaren,
whose trial results were published in The Lancet medical journal on
Thursday. "We're talking about a single one-off genetic correction
... that has long-standing effects that so far have not been shown
to diminish."
The results showed that of the six patients treated — each of them
only in one eye so the other could act as a comparison — the two
with the least good sight before the gene therapy had significantly
improved vision six months later.
In the other four patients, whose vision was only slightly
impaired before treatment as they were at earlier stages of the
condition, the results confirmed the gene therapy is safe, with the
virus delivering its DNA without damaging the retina.
"It is still too early to know if the ... treatment will last
indefinitely," MacLaren said. "But we can say that the vision
improvements have been maintained for as long as we have been
following up the patients, which is two years in one case."
He stressed that the therapy is still in the experimental stage,
with more trials likely to take up to five years before it could be
submitted for a licence with a view to making it available to all
patients.
"If we were able to treat people early, get them in their teens or
late childhood, we'd be getting the virus in before their vision is
lost," he said. "If the treatment works, we would be able to prevent
them from going blind."
(Editing by Janet Lawrence)
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