Gene therapy has partly restored the function of the retina's cone receptors in two children who were born completely color blind, reports a new study led by University College London (UCL) researchers.

The findings, published in Brain, provide hope that the treatment is effectively activating previously dormant communication pathways between the retina and the brain, drawing on the plastic nature of the developing adolescent brain.

The academically-led study has been running alongside a phase 1/2 clinical trial in children with achromatopsia, using a new way to test whether the treatment is changing the neural pathways specific to the cones.

Achromatopsia is caused by disease-causing variants to one of a few genes. It affects cone cells, which (along with rods) are one of two types of photoreceptors in the eyes. As cones are responsible for color vision, people with achromatopsia are completely color blind, while they also have very poor vision overall and find bright light uncomfortable (photophobia). Their cone cells do not send signals to the brain, but many remain present, so researchers have been seeking to activate the dormant cells.

Lead author Dr. Tessa Dekker, UCL Institute of Ophthalmology, said, "Our study is the first to directly confirm widespread speculation that gene therapy offered to children and adolescents can successfully activate the dormant cone photoreceptor pathways and evoke visual signals never previously experienced by these patients.

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