Gene Therapy Shows Early Success in Treating Common Cause of Blindness

A light-sensitive retinal protein was administered to blind mice, which showed improved awareness of their surroundings after one year.

It might be possible to reverse a common cause of blindness, retinitis pigmentosa, with the use of gene therapy, according to a University of Oxford study.

The researchers found they could increase light sensitivity in the eyes of mice, which have an inherited form of retinal degeneration, using a light-sensitive retinal protein called human melanopsin. They administered the melanopsin with a viral vector, which is a method for transferring therapeutic genes to modify cells or tissue. After one year, they observed that the mice who received the gene therapy were more aware of their surroundings than the untreated mice.

“Treated mice showed a number of visual responses including the ability to detect their environment based on visual information alone, whereas control mice were completely blind by this time point,” Samantha de Silva, lead study author and clinical research associate in medical sciences at Oxford, told Seeker. “We wouldn’t expect the mice to have the same level of vision as a completely normal mouse, but this would equate to a completely blind person being able to recognize their visual environment after treatment. It would be hugely beneficial in terms of navigation and quality of life.”

The findings were published in the journal Proceedings of the National Academy of Sciences.

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The method is unlikely to become a cure-all for every form of blindness. For example there is specific circuitry that must be maintained in the retina for it to work, but it is a big step toward treating retinal degeneration and in developing future treatments for blindness.

“[R]etinal degenerations such as retinitis pigmentosa would be the ideal conditions to treat, and this would have significant impact since they are now the leading cause of blindness in the working age population,” De Silva said. “With future developments, we hope to use this approach to target further conditions.”

The research team is confident the treatment will work in humans because the viral vector that delivered the melanopsin in the mice is based on a design that has already been effective in clinical trials. But the results will vary depending on a person’s ability to interpret the new visual signals their brain receives.

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“We know from work in our department with the bionic eye (a retinal implant that helps restore vision) that patients have to learn to interpret the new visual input,” De Silva commented. “The only way to know how much vision can be restored in patients using human melanopsin gene therapy is through a clinical trial which would be the next step in our work.”

Two other Oxford gene-replacement therapies aimed at treating choroideremia and X-linked retinitis pigmentosa are already undergoing clinical trials.

“We hope to do the same for human melanopsin gene therapy,” De Silva said. “We’re excited to see what improvements in vision we can achieve.”

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