Baby gets world's first personalised gene therapy treatment

A baby born with a rare genetic disease is "growing and thriving" after getting bespoke gene therapy.

It's the first time anyone in the world has been given an experimental gene-editing treatment designed specifically for their disease and took scientists just seven months to develop.

Nine-and-a-half-month-old KJ Muldoon, from Clifton Heights, Pennsylvania, has a rare metabolic condition - known as severe carbamoyl phosphate synthetase 1 (CPS1) deficiency - that meant he has spent the first months of his life in a US hospital on a very restrictive diet.

In February, however, the boy received the first dose of his bespoke treatment and then follow-up doses in March and April.

"We prayed, we talked to people, we gathered information, and we eventually decided that this was the way we were going to go," said KJ's father Kyle Muldoon.

KJ has been able to eat more normally and has recovered well from illnesses like colds, which can strain the body and exacerbate his symptoms.

He also now takes fewer medications.

Some experts estimate severe CPS1 deficiency affects one in a million babies. Those infants lack an enzyme needed to help remove ammonia from the body, so it can build up in their blood and become toxic.

"We're still very much in the early stages of understanding what this medication may have done for KJ," said study author Dr Rebecca Ahrens-Nicklas, a gene therapy expert at the Children's Hospital of Philadelphia (CHOP).

"But every day, he's showing us signs that he's growing and thriving."

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Considering how poorly KJ had been, "any time we see even the smallest milestone that he's meeting - like a little wave or rolling over - that's a big moment for us", said his mother Nicole Muldoon.

The team behind KJ's treatment, made up of experts from CHOP and the University of Pennsylvania, published the results of their work in the New England Journal of Medicine.

Gene therapy

Gene therapy is an innovative treatment that aims to cure disease at the source, by editing the DNA causing the problem.

The scientists working on KJ's case used CRISPR, the gene editing tool that won its inventors the Nobel Prize in 2020.

In KJ's case, the team found the disease-causing mutation in his genes and created the treatment to flip a "letter" in his genetic code to the correct type.

"This is the first step towards the use of gene editing therapies to treat a wide variety of rare genetic disorders for which there are currently no definitive medical treatments," said Dr Kiran Musunuru, a University of Pennsylvania gene-editing expert who co-authored the study.

The scientists hope that by publishing the results of their treatment quickly, it'll help others to test out similar bespoke treatments.

"Once someone comes with a breakthrough like this, it will take no time" for other teams to apply the lessons and move forward, said Carlos Moraes, a neurology professor at the University of Miami, who wasn't involved in the study.

"There are barriers, but I predict that they are going to be crossed in the next five to 10 years. Then the whole field will move as a block because we're pretty much ready."

(c) Sky News 2025: Baby gets world's first personalised gene therapy treatment