An 11-year-old girl with a rare childhood blindness condition has become just the second person in the world to receive a “revolutionary” new gene therapy.

Catherine L’Estrange, from North Acton in London, was diagnosed with the rare condition Bardet-Biedl syndrome (BBS) as an infant, according to a release from Epsom and St Helier University Hospitals NHS [U.K.’s National Health Service] Trust.

The ultra-rare condition, which affects about one in 150,000 infants, can lead to almost total vision loss by the late teens as the retina deteriorates over time.

Per the Mayo Clinic, the condition can also cause symptoms including weight gain, kidney conditions and extra fingers and toes. It’s caused by changes in genes, whether new or passed down from parents to children.

Over her life so far, Catherine became night-blind, then colorblind, and then began to lose her peripheral vision.

The preteen was the first person in the U.K. and just the second overall to receive a new retinal gene therapy at St Helier Hospital in Sutton, a town in south London. She had the treatment in March, per U.K. newspaper The Times.

The hospital also treated the world’s first person — a 17-year-old girl from Canada — to have the surgery in August 2025, per the release.

BBS can be caused by mutations in more than 20 different genes, and the treatment is available for people with mutations in the BBS10 gene, per the release. The mutations cause small cells in the retina to die, leading to blindness.

Surgeons removed the gel inside one of Catherine’s eyes and injected healthy copies of the BBS10 gene into the retina, the Press Association (PA) reported, per a release obtained by PEOPLE.

Neruban Kumaran, a consultant eye surgeon at Epsom and St Helier University Hospitals NHS Trust, told the PA, “By giving a healthy copy of the gene, it helps save those cells, and the hope is to either [stabilize] or improve vision.”

He said that tests had already been done on the patients who’ve had the surgery — since Catherine, a third child has also received treatment — and some had already said their vision in dim light had improved.

“There is a hope that it may improve vision slightly, but it’s difficult to say,” he told the PA. “It’s not going to leave someone with perfect vision. But the hope is to [stabilize] and/or improve vision. Only time will tell.”

Catherine said, “If this treatment works, it will help me to carry on seeing things around me, and most of all I will be able to carry on reading books, which is one of my [favorite] things to do.”

Her father, the Reverend Timothy L’Estrange, explained that they didn’t expect gene therapies like this one to be available for many years, and likely after Catherine had lost her sight completely.

“Most children with BBS are undiagnosed until at least primary [elementary] school age, but we had a highly unusual infant diagnosis when Catherine was just a few weeks old,” he said.

He said in the hospital’s release that the family aimed to help Catherine develop her “independence and resilience” as much as possible in advance of her vision loss.

“We were surprised and delighted when we learned this treatment had become available, and that Catherine would be one of the first patients in the world to receive it,” he added, explaining that it would be “life-changing” for her to retain any vision as a result of the treatment.

Kumaran said, per the release, that the team was “so pleased to offer this novel treatment.”

He added, “Early positive feedback from the children and their families is very exciting and offers real hope to those affected by this condition.”