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Gene therapy helps blind children to see

Sunday, 25 October 2009

Born with a retinal disease that made him legally blind, and would eventually leave him totally sightless, the nine-year-old boy used to sit in the back of the classroom, relying on the large print on an electronic screen and assisted by teacher aides. Now, after a single injection of genes that produce light-sensitive pigments in the back of his eye, he sits in front with classmates and participates in class without extra help. In the playground, he joins his classmates in playing his first game of softball.

His treatment represents the next step toward medical science’s goal of using gene therapy to cure disease. Extending a preliminary study published last year on three young adults, the full study reports successful, sustained results that showed notable improvement in children with congenital blindness.

The study, conducted by researchers from the Center for Cellular and Molecular Therapeutics at The Children’s Hospital of Philadelphia and from the University of Pennsylvania School of Medicine, used gene therapy to safely improve vision in five children and seven adults with Leber’s congenital amaurosis (LCA). The greatest improvements occurred in the children, all of whom are now able to navigate a low-light obstacle course—one result that the researchers call “spectacular.”

“This result is an exciting one for the entire field of gene therapy,” said Katherine A. High, M.D., co-first author of the study and the director of the Center for Cellular and Molecular Therapeutics, the facility that sponsored the clinical trial at The Children’s Hospital of Philadelphia. High, an investigator of the Howard Hughes Medical Institute and a past president of the American Society of Gene Therapy, has been a pioneer in translational and clinical studies of gene therapy for genetic disease. “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.”

Although the patients did not attain normal eyesight, half of them (six of 12) improved enough that they may no longer be classified as 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,” said senior author Jean Bennett, M.D., Ph.D., F.M. Kirby professor of Ophthalmology at the University of Pennsylvania School of Medicine. For Bennett, the results build on nearly 20 years of gene studies on hereditary blindness, starting with pioneering work in mice and dogs. “These remarkable results,” she added, “have laid a foundation for applying gene therapy not only to other forms of childhood-onset retinal disease, but also to more common retinal degenerations.”

The study team reported their findings today in an online article in The Lancet.

“Children who were treated with gene therapy are now able to walk and play just like any normally sighted child,” said co-first author Albert M. Maguire, M.D., an associate professor of Ophthalmology at Penn and a physician at Children’s Hospital. “They can also carry out classroom activities without visual aids.”

Maguire and Bennett have been researching inherited retinal degenerations for nearly 20 years. Leber’s congenital amaurosis (LCA), the target of this current study, is a group of inherited blinding diseases that damages light receptors in the retina. It usually begins stealing sight in early childhood and causes total blindness during a patient’s twenties or thirties. Currently, there is no treatment for LCA.

For children and adults in the study, functional improvements in vision followed single injections of genes that produced proteins to make light receptors work in their retinas.
Walking along a dimly lit, simulated street route, the children were able to negotiate barriers they bumped into before the surgery. Another child, who since birth, could only see light and shadows, stared into his father’s face and said he could see the color of his eyes. Later they played soccer together.

The 12 subjects ranged in age from 8 to 44 years old at the time of treatment. Four of the children, aged 8 to 11, are the world’s youngest individuals to receive gene therapy for a non-lethal disease (A fifth subject was 17 years old). On the other end of the age scale, the 35-year-old man and 44-year-old woman are the oldest patients to ever receive gene therapy for retinal degeneration.