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Blind man regains partial vision after optogenetic therapy

1 June 2021
Appeared in BioNews 1097

A new type of gene therapy has helped a man regain some vision after 40 years.

The French man, who was diagnosed with retinitis pigmentosa (RP) in his teens, began to show signs of visual improvement a few months after the therapy, and was able to see things like the stripes of a pedestrian crossing, and objects on a table in from of him. 

'The findings provide proof of concept that using optogenetic therapy to partially restore vision is possible,' said co-author Professor Botond Roska, from the Institute of Molecular and Clinical Ophthalmology in Basel, Switzerland.

RP is a group of rare, genetic eye diseases where the light-detecting 'rod' and 'cone' cells in the eye gradually break down, leading to progressive loss of vision. There are different types of RP caused by different genes, this can affect the age of onset and the speed of degeneration, but together they affect around 1 in 4000 people worldwide. 

Optogenetic therapy offers patients a new way to detect light, rather than replacing the specific gene at fault. Thus it has the potential to treat vision loss from a variety of genetic causes, unlike traditional gene therapies which are specific to the gene causing the problem.

'Importantly, blind patients with different kinds of neurodegenerative photoreceptor disease and a functional optic nerve will potentially be eligible for the treatment,' said first author Professor José-Alain Sahel, chairman of ophthalmology at the University of Pittsburgh, Pennsylvania. 'However, it will take time until this therapy can be offered to patients.'

A traditional gene therapy (which seek to replace the faulty gene) does exist for one of the early-onset forms of the disease, but because RP can be caused by mutations in any of 71 different genes, it will not work for many patients. Not only that, but in RP once the light-sensitive cells have died they cannot be replaced, so traditional gene therapies can only be effective as an early intervention before the cells have gone.

Instead of replacing the faulty gene, the optogenetic approach delivers instructions to help cells in the retina (that are not normally light-sensitive) make a different light-sensitive protein called ChrimsonR which can sense amber light. This is paired with goggles that translate images in front of the patient into amber wavelengths that the new protein can detect. The idea has been around since the early 2000s but this study, published in Nature Medicine, is the first reported success in a human trial.

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