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Scientists have claimed a world first for a new form of gene therapy that could help the blind to see.
Specialists at University College London and Moorfields eye hospital are testing the revolutionary treatment on 12 patients, aged 8 to the mid-20s, with an inherited eye disorder in the first trial of its kind.
The technique has been shown to work in animals affected by the same disorder, inherited retinal degeneration, whose sight was restored.
If proved successful in humans, the scientists hope the technique can be extended to other eye diseases.
Professor Robin Ali, who is leading the research, said it was "very exciting" and represented "a huge step towards establishing gene therapy for the treatment of many different eye conditions".
But he warned the work was at an early stage aimed at establishing the safety and efficacy of gene transfer to the eye and that gene therapy for conditions including macular degeneration, which affects an estimated 500,000 mainly elderly people in Britain, was many years away.
Professor Ali said: "The advantage of using gene therapy over drugs is that you can give it as a single treatment ... We anticipate the gene transfer is life long."
Robert Johnson, 23, one of the 12 patients in the trial, was born with an inherited disorder called Leber's congenital amaurosis, which has caused his sight to progressively deteriorate.
He is able to see outlines of objects in daylight but very little after dark and he has been told that his sight will worsen as he ages.
On the day of his operation a few weeks ago, he told the BBC his mood was swinging from "extreme nervousness" to "a bit of excitement". It will be months before he experiences any benefits from the treatment and only then will the researchers be able to declare it a success.
Mr Johnson's disorder is caused by a fault in a single gene. The operation involved injecting normal versions of the defective gene into the pigment cells at the back of the eye. The gene is carried by a virus, modified to render it harmless, which inserts it into the cells' DNA.
The procedure had never been attempted and was the riskiest part of the treatment, requiring extreme surgical precision. In order to deliver the gene to as many cells as possible, a large volume of solution was injected, sufficient to lift the retina, causing a temporary detachment. The retina is delicate and one slip could have torn it, destroying Mr Johnson's remaining sight. Mr Johnson was monitored to ensure his retina reattached within 24 hours.
James Bainbridge, consultant ophthalmologist at Moorfields, who carried out the operation, said he was pleased with the outcome but there was no guarantee of success.
The research team have been experimenting with gene therapy for 15 years but this is the first trial in humans. Dogs affected by the eye disorder who were treated with the technique had their vision improved to the point where they could walk through a maze without difficulty, which they had previously been unable to do.
As inherited retinal degeneration is a progressive disorder, the best results are likely to be seen in the youngest patients whose sight has deteriorated least.
Professor Tony Moore, a University College retinal specialist and part of the research team, said: "Some indications of the results of the trial may be available within months. It will be many months before we have the full picture. We anticipate the best outcome in younger patients, where the disease is in the early stages of its development."
The announcement of the trial was welcomed by specialists in genetics. Professor Leonard Seymour, president of the British Society for Gene Therapy, said: "The retina is a really good place for gene therapy because it can be accessed by direct injection - overcoming the problem of gene delivery. When gene delivery is efficient, the whole power of gene therapy is unleashed."
The research is supported with £1 million ($2.7 million) from the Department of Health. Health Minister Lord Hunt says the UK leads Europe in gene therapy with over 40 per cent of clinical trials, second only to the US.
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