Gene therapy against congenital blindness: another good result!
A new victory has just been won against amaurosis Congenital Leber, which most often leads to complete blindness in adulthood. Last year, four people had recovered some of their vision. Today, the same genetic technique has proven itself by demonstrating that it works much better in children.
9-year-old Corey Haas is now able to ride a bike, and a video shows him walking along a signposted path full of obstacles. Yet, Corey was born with one of the forms of Leber's Congenital Amaurosis (or LCA, its English name). This disease, which affects the photoreceptors, causes a big deficit of vision at birth which evolves most often in a total blindness towards forty years. We know today that the cause is genetic. One of the genes needed to synthesize a photoreceptor works poorly. Several genes are involved and so there are as many forms of this disease (at least 11 currently known).
Corey is suffering from the so-called LCA2 form. At home, it is the RPE65 gene that hurts its work whereas it should induce the synthesis of rhodopsin, one of the pigments of the retina, present in the sticks. These cells end up, over the years, by dying.
For years, researchers have been exploring the path of gene therapy to combat several forms of genetic blindness, including Leber's amaurosis. In 2006, a team from Inserm Nantes managed to partially restore the sight to dogs suffering from this disease (also due to a mutation of the RPE65 gene). In April 2008, a big first was announced in humans. Two independent teams, in the United States (University of Pennsylvania) and the United Kingdom (University College, London), improved the vision of four people with ACL2 out of the eight who received treatment.
In both cases, the method consists in integrating an RPE65 gene in a harmless adenovirus introduced into the retina, so that it then enters the photosensitive cells. This is the same way the Pennsylvania team used again today, announcing excellent results today.
Two years without side effects
Two years ago, Albert Maguire, Jean Bennet and their colleagues treated 12 patients, aged 8 to 44, including four children, the oldest being 11 years old. The results, which have just been published in The Lancet, show that in all cases, vision has improved significantly, according to experimental measurements and according to subjective criteria. Above all, the study shows what had already been noted in dogs, namely that the method gives much better results in the young.
The injection of the RPE65 gene, in fact, will have even more effects as the target cells still alive are more numerous. As the disease progressively leads to the death of these cells, the impact of treatment diminishes with age. The researchers note that the youngest of the 8-year-old treated children regained a sensitivity to light identical to that of a normal child of the same age. The positive effects are felt in the first months after treatment and have continued during the two years of the study, without undesirable side effects.
The gene therapy has just again scored points, at least against the congenital amaurosis of Leber. Other recent studies in mice show good results for another disease, retinitis pigmentosa and color vision have been restored in squirrel monkeys. However, there is still a lot of work to be done, starting with clinical trials on a larger number of patients.
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