Genetic breakthrough for blindness

New gene therapy restores some sight in
people born with inherited form of blindness Posted in: Medical Science News | Medical Research News | Medical Condition News Published on January 16, 2014 at 8:17 AM A new gene therapy has restored some sight in
people born with an inherited, progressive form of
blindness. The technique replaces a defective gene
in the eye with a normal working copy of the gene
using a single injection. The findings of this phase 1 trial, published in The
Lancet, support the further development of this
state-of-the-art treatment for other more common
genetic causes of blindness including degenerative
diseases of old age, such as macular degeneration,
and inherited defects like retinitis pigmentosa. Choroideremia is caused by a mutation in the CHM
gene on the X chromosome and affects an
estimated 1 in every 50 000 people. The condition
causes progressive loss of vision due to
degeneration of the choroid, retinal pigment
epithelium, and retina. There is no treatment for choroideremia and eventually the photoreceptor
cells—the rods and cones in the retina that respond
to light by sending signals to the visual processing
areas of the brain—also degenerate leading to
complete blindness by middle age. “The cellular degeneration in this disease is fairly
slow, providing a reasonably large window of time in
which to intervene before the onset of visual loss”,
explains Professor Robert E MacLaren from the
University of Oxford in the UK who led the research. MacLaren and colleagues assessed the effect of
gene therapy on retinal and visual function in six
patients aged 35–63 years with different stages of
choroideremia. They injected patients’ retinas with a
vector—a genetically engineered adeno-associated
virus (AAV)—to deliver a corrective copy of the gene into the appropriate part of the eye to halt
photoreceptor cell death. The treatment caused no harm and resulted in
improvements in subjective measurements of
vision. Six months after delivery of the gene, all
patients recovered their visual acuity from before
the procedure, and two patients showed substantial
improvements in how well they could see, with one reading over three additional lines on an eye chart.
Importantly, the patients developed increased
sensitivity to light, compared to a loss in sensitivity
in the untreated eyes. According to Professor MacLaren, “This is first time
that gene therapy has been used to treat patients
with normal visual acuity before the onset of
clinically significant retinal thinning. Our findings
hold great promise for gene therapy to prevent loss
of sight in other retinal diseases such as age-related macular degeneration.” Writing in a linked Comment, Hendrik Scholl from
John Hopkins University, Baltimore, USA, and José
Sahel from the Institut de la Vision, Paris, France,
say, “The ultimate goal of gene therapy in
choroideremia would be to save the central retina
from further degeneration. The short follow-up of the new study prevents any conclusion about preventing
degeneration in the long term; indeed, results from
the morphological assessment suggested that
degeneration is rather continuous…It remains to be
determined if gene therapy targeting REP1 will have
an effect on the progression of photoreceptor degeneration. Even if the effect turns out to be only
slight, this might have important positive
implications because there are additional therapeutic
avenues targeting photoreceptors that could help to
save or restore visual function." Source: http://www.thelancet.com/