Gene therapy partially restored color vision in colorblind people

(ORDO NEWS) — Scientists managed to partially restore the function of cones (retinal photoreceptors that provide color vision) to two children born with achromatopsia – complete color blindness. Researchers have used gene therapy to repair the neural connection between the retina and the brain.

Monochromasia is a complete lack of color perception, absolutely normal for some animal species, such as cetaceans and some pinnipeds. In humans, this is a pathological condition called achromatopsia, color blindness, or complete color blindness.

It is caused by a mutation in one or more genes that code for cone proteins, one of two types of retinal photoreceptors.

Since cones are responsible for color vision, people with achromatopsia perceive the color of any wave as gray and distinguish only its brightness.

In addition, they have poor eyesight, they suffer from photophobia and nystagmus – involuntary oscillatory movements of the eyeballs.

In achromatopsia, cones do not send signals to the brain, but they may be present on the retina. Scientists from University College London (UK) have found a way to activate these dormant cells in order to partially restore color perception to patients with complete color blindness.

Four adolescents with achromatopsia aged 10 to 15 were selected for the experiment. Children’s brains are more neuroplastic than adults’ because neural connections develop more actively at an early age.

Gene therapy included the introduction of adeno-associated viral vectors expressing the CNGA3 or CNGB3 genes associated with color blindness.

Mutations were found in these genes in four patients. The treatment was performed on only one eye, so that scientists could fully evaluate the result.

The researchers used functional magnetic resonance imaging (fMRI) to separate new brain signals that emerged after treatment from pre-existing signals.

This made it possible to accurately record all changes in visual function. In the experiments, pairs of light sources were used to selectively stimulate cones or rods.

The results were compared with tests in which patients with achromatopsia and healthy volunteers took part.

Six to 14 months after treatment, two of the four children had signals sent from the cones of the treated eye to the brain. Their fMRI scores now resembled those of study participants with normal vision.

The subjects also underwent a psychophysical test that assessed their ability to distinguish levels of contrast. The same two children showed marked improvement in vision.

While the researchers cannot confirm that the treatment of the other two participants was ineffective – perhaps the result will appear later.

In addition, the study demonstrated unprecedented neuronal plasticity in children’s brains, raising hope that gene therapy can reactivate visual functions and neural pathways that have been dormant for years.

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