Nine-year-old Corey Haas can ride his bike alone now, thanks to an experimental gene therapy that has boosted his fading vision with a single treatment.
The gene therapy helped improve worsening eyesight caused by a rare inherited disease called Leber congenital amaurosis, or LCA, which makes most patients blind by age 40.
Twelve treated patients, including Corey, now have better vision, their doctors told a joint meeting of the American Academy of Ophthalmology and Pan-American Association of Ophthalmology in San Francisco on Saturday.
"All 12 patients given gene therapy in one eye showed improvement in retinal function," Dr Katherine High of The Children's Hospital of Philadelphia and the Howard Hughes Medical Institute and colleagues wrote in a report to be released at the same time by the Lancet medical journal.
LCA causes the retina to degenerate and the researchers found that the younger the patient treated with the therapy, the better the effects.
"Before, I used to ride my bike just in front of the house and now I just ride around the neighborhood with no one watching," Corey told a news conference.
While the experiment was meant mostly to show the treatment was safe, it showed remarkably strong effects, High and Dr Jean Bennett of the University of Pennsylvania found.
"This study reports dramatic results in restoring vision to patients who previously had no options for treatment," said High. "These findings may expedite development of gene therapy for more common retinal diseases, such as age-related macular degeneration."
They could also help restore the tarnished image of gene therapy, battered by the death of an 18-year-old volunteer in a clinical trial in 1999 and cases of leukemia in a few young children treated in France.
"The study by Bennett and co-workers will further boost gene therapy trials and provide hope for patients with inherited blindness and other genetic disorders," Dr Frans Cremers and Dr Rob Collin of Nijmegen Medical Center in the Netherlands wrote in a commentary.
A faulty gene means patients with LCA start to lose their vision in childhood. There is no treatment.
High, Bennett and colleagues worked with 12 volunteers, aged 8 to 44. They reported on three of the adult patients in April of 2008.
They designed a harmless virus, called an adeno-associated virus, to carry corrective DNA directly into the eyes. The gene they used, called RPE65, is mutated in up to about 16 percent of LCA patients and the normal gene restored light-sensitive pigments in the retina at the back of the eye.
The treatment did not restore normal eyesight to any of the patients but half are no longer legally blind.
"The clinical benefits have persisted for nearly two years since the first subjects were treated with injections of therapeutic genes into their retinas," Bennett said.
Four children aged 8, 9, 10, and 11 can now walk unaided.
Corey's father, Ethan Haas, from Hadley, New York, said they embraced the experiment.
"You start to think of what could happen — he could go completely blind. And then it's like, well, he may go blind in the future anyway because it's degenerative, so I decided to try it now and see if we could stop it and correct it," Haas said.
Corey's mother, Nancy Haas, said it was worth the risk.
"It's hard to see a child not be able to play like he should with his other friends, and then to have shortly after surgery, he's out there with his friends, playing, being able to see things coming from his peripheral vision, noticing other kids," she said, beginning to cry.
"It's all worth it."