thérapie génique daltonisme

Color blindness: Gene therapy partially restores cone function in children

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There is currently no treatment for color blindness, a genetic condition that affects color vision and affects millions of people worldwide. Gene therapy has made great strides in recent years in hopes of leading to effective treatments for diseases. Researchers at University College London used brain plasticity and attempted an early gene therapy approach to activate cone cells in the retinas of four children with complete 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 in different forms. Achromatopsia, which is a “total” disease, is caused by mutations in certain genes and affects the cone-shaped photoreceptors in the retina that are responsible for color perception. People with complete color blindness also generally have poor eyesight, photophobia (can’t stand bright light), and also something called nystagmus (involuntary wiggling of the eyes).

In these people, the cone cells are partially or completely inactive, sending little or no signals to the neurons. Because each of these cones is responsible for perceiving a specific range of colors, color-blind people perceive colors poorly or not at all when these cells are inactive.

In fact, the hereditary disease is more common in men than in women because the mutation is carried by the X chromosome, and although the majority of cases are benign, it represents a problem for patients who tend to be stigmatized and discriminated against daily challenge do not have access to certain activities and professions.

Because the cone cells are present in every individual from birth, therapeutic options for color blindness are currently focused on the means of activating these cells, the latter being “dormant” in patients. In recent years, the achievements of gene therapy have shown positive results in non-primate and primate models, raising hopes for 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, suggesting that processing may occur at the level of the neural pathway specific to these cells.

We demonstrate the potential of harnessing the plasticity of the brain, which can adapt to the effects of treatment, particularly at a young age ‘ explains Tessa Dekker, first author of the new study, which was published in the journal Brain, and researchers in the Department of Ophthalmology at University College London. According to the expert, this study would be the first to confirm the widely held hypothesis that gene therapy given to children and adolescents can successfully activate the pathways of photoreceptors in dormant cones and enable visual signals never before seen in this type of patient have been seen before.

Positive results in two out of four children

To test the new therapy, four children (10 to 15 years old) with color blindness took part in two different studies. Both studies each targeted a specific gene and targeted genes that are known to cause the disease. Using a functional MRI (fMRI) mapping approach, post-treatment cone cell signals could be measured to monitor any changes in activity.

After the treatments were administered, the children’s eyes were stimulated with light sources that selectively targeted rod and cone cells. The nystagmus of the subjects was also taken into account. The results were then compared to those of nine untreated patients and 28 subjects with normal vision. The four color-blind children only received the treatment in one eye 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 administration of the treatment. The activity of the cells was very similar to that seen in healthy people and this type of activity had never been seen in affected patients before taking the treatment.

Participants also performed psychophysical tests to assess their eyes’ ability to perceive different contrasts and colors. Cone cell-related cognition was significantly improved in the above two children.

According to the researchers, the effectiveness of the therapy cannot be ruled out in the two other color-blind children treated, as the effects could occur later. It is also possible that the tests performed to detect an improvement in visual acuity are not sufficiently adapted. In addition, not all results have been compiled yet. The actual effectiveness of the treatment should therefore be re-evaluated.

Source: brain


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