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Gene therapy
restores sight to blind dogs
A team of scientists led by Jean Bennett, at the University of Pennsylvania, reported their success in this month's Nature Genetics. Their experiment involved dogs with Leber congenital amaurosis (LCA), a form of blindness, that also affects human infants and for which there is no treatment. The disease involves a defect in the genes responsible for the retina's ability to translate light into nerve impulses. In humans, LCA causes severe rapid onset of blindness, a process which begins before birth so infants are born partially blind. The researchers said most efforts to treat LCA have focussed on trying to slow retinal degeneration and eventual blindness, but the restoration of sight to a blind eye has not been successful until now. Bennett's team injected the eyeballs of dogs born with LCA with cells modified to contain the appropriate functional genes which restored the animals' sight. Humans are next "This is a dog model of a human disease," said Dr Jonathon Stone of Sydney University who studies the environmental factors contributing to blindness. "It's impressive that the researchers have shown such a degree of improvement in sight - a several fold increase." However, Dr Stone told ABC Science Online that applying this work to humans would not be immediate nor straightforward. "In the dog, LCA shows a slow progression and so the researchers were able to work with adult dogs," he said. "In humans, any gene therapy would have to occur before birth". Dr Stone said a further challenge would be identifying the exact genetic defect for LCA. "Different people with LCA have defects in different genes, or different parts of the same gene, and this varies from one continent to another," he said. He was confident, nevertheless, that geneticists could achieve this. Sydney University biochemist Dr Merlin Crossley, who works on inherited diseases of the blood, was also excited about the report. Genetic cures becoming reality "People have always regarded genetic conditions as a sentence for life," he told ABC Science Online. "But this experiment seems to have cured a genetic disease". He said while the experiment only lasted four months, in the context of previous failures with gene therapy, this was a major advance. "You must see it in the context of the field," he said. "Since the first experiments in the 1980s there have been many disappointments. Only since last year have there been positive results". Dr Crossley said recent advances used the relatively new type of vector, called an adeno-associated virus, to deliver the functioning gene. Given safety concerns recently following the widely publicised death of a gene therapy trial participant, Dr Crossley said any medical intervention would have side-effects and caution was needed. LCA is one of a number of forms of retinal degeneration which affect 1 in 4,000 people. Anna Salleh - ABC Science
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