314
million
number of people
with visual impairments worldwide
45
million
number of those
people who are
totally blind
85
percent
portion of visual impairment
cases called “avoidable” by
the World health organization
Gene therapy helps blind mice see
sight restored in cone cells impaired by retinitis pigmentosa
When stimulated by light, those proteins
open up and let negatively charged ions
into the cell. When inserted and active
in the mouse cell membranes, the pro-
teins helped mimic the normal activity
of healthy cones.
Not only did the restored cone cells
respond to light, but they also sent signals
to the brain so the mice could see.
“What was really astounding is that
these cells that were blind for a while
were still connected to the rest of the circuit,” says neurobiologist Botond Roska,
who led the study.
By Gwyneth Dickey
Researchers have restored sight to blind
laboratory mice by using gene therapy.
If it works in people, the new treatment
may one day allow some with retinitis
pigmentosa, an incurable genetic eye disease, to navigate a room, read and drive.
“It’s an excellent study,” says develop-
mental neuroscientist Connie Cepko of
Harvard Medical School, who was not
involved with the research. “This is con-
ceptually a nice way to try to restore or
prolong vision.”
Retinitis pigmentosa causes tunnel
vision and night blindness in 2 million
people worldwide. It primarily affects
rods, light-sensitive cells concentrated
in the outer retina
that enable night and
peripheral vision.
Some patients also
lose daylight vision
and go blind completely as the color-sensing cone cells
of the inner retina
slowly degenerate.
Mice cone cells glow green where
a therapeutic gene hit its target.
But the disease
doesn’t kill cone cells
immediately; it first makes them nonresponsive to light. That means there is a
window of time when the cone receptors
are still there, but not functioning.
So a team led by scientists at the
Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland, attempted to reanimate diseased
cone cells in mice. Using a virus already
approved for human gene therapy, the
researchers inserted a gene from a light-sensitive bacterium, Natronomonas
pharaonis , into the DNA of cone cells, the
team reported online June 24 in Science.
But unlike healthy cone cells, the
restored cone cells could not adapt to
different light levels. The cells responded
best to bright yellow light similar to sunlight at the beach, Roska says. In order
for human patients to
see in dimmer light,
researchers would
have to develop special glasses with light-sensing cameras to
adjust the intensity of
light projected to the
patients’ eyes, he says.
After more studies
with mice and primates to ensure the
treatment’s safety and effectiveness,
Roska aims to test it in human patients.
“This is not a treatment for all patients
with retinitis pigmentosa,” he says,
“but for a subgroup in which the cone
receptors are still there.”
His team will also explore how long
the therapeutic effects last and whether
the gene therapy could have applications for other eye diseases like macular
degeneration and retinal damage due
to diabetes.
The gene is a blueprint for proteins that
form passageways in cell membranes.
“I have a feeling it will make it into
human trials,” says Cepko. “How a person will perceive these signals is hard
to say, but it should do at least as well as
it did for mice.” s
Stopping platelets at the source
slowing the production of clot-forming
platelets may protect against heart
attack and stroke without the risk of
excessive bleeding posed by aspirin,
scientists say in the June 23 Science
Translational Medicine. clots in arteries cause most strokes and heart
attacks, but reducing clotting too
zealously places a person at risk of
bleeding to death. stephen hanson
of the oregon health & science university in portland and colleagues
used an antibody to limit the outflow
of clot-forming platelets from bone
marrow in baboons. the antibody
inhibits thrombopoietin, a hormone
that spurs cells in the bone marrow to make platelets. by keeping
platelet levels at the low end of the
normal range, the drug substantially
limited clot formation without causing
excess bleeding. — Nathan Seppa
Vitamin may cut lung cancer risk
it might be too soon to start popping supplements, but high levels of
vitamin b6 may reduce lung cancer
risk, scientists report June 16 in
the Journal of the American Medical
Association. researchers also note
possible benefits from high levels
of folate and of the amino acid
methionine. using medical data from
more than 380,000 europeans, an
international team calculated that
people with vitamin b6 levels in the
top quarter of all samples had about
half the risk of lung cancer as those
with the lowest vitamin b6 levels. a
similar benefit was found for methionine. high folate levels seemed to
give less protection (and only for
smokers). having stellar levels of all
three lowered the risk of lung cancer
by a full two-thirds, the scientists
calculated. — Nathan Seppa
www.sciencenews.org
July 17, 2010 | science news | 11
