August 13, 2009
Gene Therapy Shows Promise In Three Blind Patients
U.S. researchers said on Wednesday that a year after receiving gene therapy for a condition that causes total blindness by age 30, three people continue to see better and one has improved enough to read the digital numbers on a clock, Reuters reported.
Doctors involved in the experiment reported in the New England Journal of Medicine that improvements in the vision of the three volunteers, who were all in their 20s and legally blind, has not deteriorated over time.
One of the subjects has even developed a kind of "second sight" because her brain has learned to tap information from an area of the retina rejuvenated by gene therapy.
Dr. Artur Cideciyan of the University of Pennsylvania said the initial improvements were very substantial and occurred in a matter of weeks.
However, he noted that the one patient's vision has continued to improve because her brain has apparently learned to use information from the treated portion of the eye, giving her the ability to read the clock.
Cideciyan called it "very encouraging" to see that the adult brain seems to be adapting to this vision.
The two men and the woman in the experiment suffer from a form of Leber's congenital amaurosis, an otherwise-untreatable condition that causes a loss of vision in infants and children. A gene known as RPE65, which produces a special form of vitamin A for retinal cells, was defective in all three subjects, causing them to be legally blind since birth.
Researchers have been attempting to fix genetic problems by injecting properly functioning DNA into a virus and using the virus to deliver the healthy DNA to individual cells.
In the recent attempt, all three patients were able to detect dim lights they were previously unable to see before the treatment just 3 months after doctors injected them in the eye with healthy versions of the gene.
The female patient was even able to use her right eye -- which was initially her worst -- to read a dashboard clock for the first time in her life.
She was seeing the light using a portion of the eye that had been injected with the healthy DNA, and not the usual spot used for reading and seeing detail, the researchers said.
Cideciyan said she either uses her normal gaze straight ahead or, under other conditions, she switches to this treated area.
"So she has two loci for gaze and she switches between the two. That took a while to occur," he said.
The team noted that the therapy has not caused an immune response in the eye or in the body a year after their treatments began.
"The RPE65 gene therapy appears to be safe and leads to a stable visual improvement in the patients studied. We are cautiously optimistic about these results and look forward to additional reports that address the key issues of safety and effectiveness," Cideciyan said in a statement
The patients will continue to be monitored over several years and they are experimenting with other patients to see if injecting different amounts of DNA is more effective.
Some 2,000 people in the United States are affected by Leber congenital amaurosis type 2 -- one of several incurable forms of blindness collectively known as retinitis pigmentosa, which affects about 200,000 Americans.
Gene therapy research suffered a serious setback in 1999 after the death of a volunteer in a University of Pennsylvania study who received a corrective gene in a deactivated virus to treat a liver defect. The test subject died four days later.
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