Friday, August 14, 2009
Gene Therapy Creates a New Fovea
Treatment leads to an unexpected improvement in vision for one patient.
By Emily Singer
Twelve months after receiving an experimental gene therapy for a rare,
inherited form of blindness, a patient discovered that she could read an
illuminated
clock in the family car for the first time in her life. The unexpected findings
suggest that the brain can adapt to new sensory capacity, even in people
who have been blind since birth.
The patient, who remains anonymous, suffers from a disease called Leber
congenital amaurosis, in which an abnormal protein in sufferers' photoreceptors
severely impairs their sensitivity to light. "It's like wearing several pairs
of sunglasses in a dark room," says Artur Cideciyan, a researcher at the
University of Pennsylvania in Philadelphia, who oversaw the trial.
At the start of the study, physicians injected a gene encoding a functional
copy of the protein into a small part of one eye--about eight-to-nine
millimeters
in diameter--of three patients, all in their twenties and blind since birth. In
preliminary results published last year, Cideciyan and colleagues found
that all three patients showed substantial improvements in their ability to
detect light three months after treatment.
The researchers have now published new results of the study in the journal
Human Gene Therapy, showing that these improvements remained stable after one
year. And in a letter to the New England Journal of Medicine, they describe
surprising gains in one patient's vision. "It was unexpected because the major
improvement of vision had occurred within weeks after the treatment," says
Cideciyan.
Probing further, the researchers found that the patient appeared to be using
the treated part of her eye like a second fovea--the part of the retina that
is most densely populated with photoreceptors and is typically used for
detailed vision, such as reading. The patient could detect dimmer light using
the
treated region than she could with her natural fovea. "We realized she was
slowly adapting to her newfound vision by subconsciously focusing her attention
to the treated area as opposed to the untreated central fovea," says Cideciyan.
"It suggests that there is a plasticity, an ability to adapt in the adult
visual brain."
"It's very encouraging," says Kang Zhang, an ophthalmologist and director of
the Institute for Genomic Medicine at the University of California, San Diego,
who was not involved in the study. "The formation of almost another vision
center has implications as we go forward for patients with congenital blindness.
They might not be able to use their normal fovea, but they might be able to
develop a new center of vision."
Researchers now plan to study other patients in the trial to determine if they
have experienced similar improvements. They also hope to figure out how
to accelerate these gains, perhaps by using visual training targeted to the
area treated with gene therapy.
The scientists also say that the fact that patients' visual improvements held
for a year after injection is promising. "It means that for congenital or
childhood blindness," says Zhang, "there is the potential to at least
stabilize, if not improve, visual function."
Copyright Technology Review 2009.
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