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Gene Therapy May Reverse Blindness

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Posted by on Monday, February 14, 2011, 5:55
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Gene therapy is a highly controversial topic, in both the political and moral arenas. Scientists have made great strides in certain areas of experimental testing, the most recent involving Leber’s congenital amaurosis, a rare type of blindness that affects approximately 2,000 Americans.

Gene Therapy May Reverse Blindness
Gene Therapy May Reverse Blindness

Currently, there is no known treatment for the disease which occurs in infancy and can cause severe loss of vision, particularly at night.

On Sunday, the New England Journal of Medicine published the scientific findings online. According to the report, the treatment showed great success in four of the six participants who received the treatment. Two of the participants who could previously see nothing more than hand motions were able to read a part of an eye chart within a few weeks.

Experts believe that if the studies are successful in large numbers the technique may be able to reverse blindness caused by other inherited diseases.

“It’s a phenomenal breakthrough,” said Stephen Rose, Chief Research Officer of the Foundation Fighting Blindness. The Foundation was one of the funding sources for a study performed at Children’s Hospital of Philadelphia.

“I think this is incredibly exciting,” said Dr. Jean Bennett, a professor of ophthalmology at the University of Pennsylvania and a leader of the Philadelphia study. “It’s the beginning of a whole new phase of studies.”

The concept behind gene therapy is relatively simple. Scientists have discovered the technique in which they can replace faulty genes, potentially curing the problem. Various gene therapy studies have been used on humans for the past fifteen years with some success.

There have been failures. A 1999 study at Penn resulted in the death of Jesse Gelsinger, 18, who was being treated for a liver disorder. There have also been children treated for “bubble boy disease”, a rare immune disorder, which later developed leukemia.

Scientists are optimistic the early results of the vision experiments will give the field a boost.

“I think it’s really a big shot in the arm for gene therapy and for medicine in general,” said Dr. Ronald Crystal, head of Genetic Medicine at Weill Cornell Medical College in New York.

Each of the participants showed mutations in a gene that produces a protein required by the retina. The retina is responsible for sensing light and sending images to the brain. Those without the gene gradually lose their vision and become blind in early adulthood.

Although the participants have the disease, their retinas tend to remain relatively healthy for a while, making the participant “a good candidate for gene therapy”, said Robin Ali, a professor at University College London, who led a British team. Ali compared the defective gene to a car that is missing a spark plug engine.

“The whole engine can be absolutely fine, but if it doesn’t have a spark plug, the car’s not going to work,” said Ali.

The experiment consisted of scientists injecting millions of copies of a “working gene” beneath a participant’s retina in the back of the eye. Only one of the patient’s eyes was treated — the worst one — in case anything went awry. The untreated eye was used a part of a control group. After the treatment, eyesight and light sensitivity were measured periodically. Later, the participant’s mobility was tested using a maze or an obstacle course.

Three participants treated in Philadelphia showed significant improvement with their sight, said researchers. The participants, two women and one man, were from Italy, where they had been previously screened by researchers there. To date, the longest follow-up on a participant has been six months.

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