thérapie génique daltonisme

Color blindness: gene therapy partially restores cone function in children

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Currently, there is no treatment for color blindness, a genetic condition that affects color vision and affects millions of people around the world. In recent years, gene therapy has made great strides in the hope of resulting in an effective treatment for the disease. Harnessing the plasticity of the brain, researchers at University College London attempted an early gene therapy approach to activate cone cells in the retinas of four children with total color blindness. Result: the therapy partially activated the dormant cones. A world first.

Depending on the person and the identity of the mutated gene, color blindness can manifest itself in different ways. In the case of achromatopsia, where the disease is said to be “total”, it is caused by the mutation of certain genes and affects the cone photoreceptors of the retina, the latter being responsible for color perception. People with total color blindness also have poor eyesight in general, photophobia (can’t stand bright light), and also something called nystagmus (involuntary eye movement).

In these people, the cone cells are completely or partially inactive and send little or no signals to the neurons. As each of these cones is responsible for the perception of a specific range of colors, colorblind people do not perceive colors or do so poorly when these cells are inactive.

In other words, the hereditary disease has a higher prevalence in men than in women, because the mutation is carried by the X chromosome. And although most cases are treated in a benign way, it represents daily challenges for patients, who tend to to be stigmatized and do not have access to certain activities and professions.

As cone cells are present in every individual from birth, therapeutic approaches against color blindness currently focus on means to activate these cells, the latter being “asleep” in patients. In recent years, gene therapy exploits have shown positive results in both primate and non-primate models, raising hope for a clinical treatment.

The researchers in the new study then tried to harness the plasticity of the developing brains of children with color blindness by giving them early gene therapy. In two children born with achromatopsia, cone receptors were partially activated, implying that processing may occur at the level of neural pathways specific to these cells.

We demonstrate the potential to harness the plasticity of the brain, which may be particularly capable of adapting to the effects of treatment when people are young. explains Tessa Dekker, lead author of the new study, published in the journal Brainand researcher in the department of ophthalmology at University College London. According to the expert, this study would be the first to confirm the widespread hypothesis that gene therapy administered to children and adolescents can successfully activate photoreceptor pathways in latent cones, and allow visual signals never seen before in this type of patient.

Positive results in two out of four children

To test the new therapy, four children (ages 10 to 15) with color blindness participated in two different trials. Each targeting a specific gene, both trials targeted genes known to cause disease. Using a functional MRI (fMRI) mapping approach, cone cell signals could be measured after treatment, to track any changes in activity.

After administration of the treatments, the children’s eyes were stimulated with light sources that were selectively aimed at the rod and cone cells. The nystagmus of the subjects was also taken into account. The results were then compared with those of nine untreated patients and 28 volunteers with normal vision. The four colorblind children only received the treatment in one eye, so they were able to compare its effectiveness with the untreated eye.

In two of the treated diseased children, signals emanating from the cone cells of the treated eye were observed 6 to 14 months after treatment administration. The activity of the cells was very similar to that observed in healthy individuals, and this type of activity was never observed before taking the treatment in the patients in question.

The participants also took psychophysical tests to assess the ability of their eyes to perceive different contrasts and colors. Perception related to cone cells was significantly improved in the two children mentioned above.

In the other two color blind children treated, the effectiveness of the therapy cannot be ruled out according to the researchers, because the effects could occur later. It is also possible that the tests that are carried out to detect an improvement in visual acuity are not sufficiently adapted. Also, not all results have been compiled yet. Therefore, the real efficacy of the treatment should be reassessed.

Source: Brain

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