3-Year-Old Boy with Rare Condition Amazes Doctors by Becoming World's First Gene Therapy Patient

A California toddler is thriving after becoming the first person in the world with his rare genetic condition to be treated with gene therapy.

Three-year-old Oliver Chu was born with mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome. His older brother Skyler was also born with the condition. It causes the body to have difficulty breaking down certain sugar molecules, according to the Cleveland Clinic. 

As those molecules build up in the organs and tissues, it can lead to damage that affects physical and mental development. Symptoms include stiff joints, thickening of facial features, hearing loss, delayed growth, breathing and heart troubles and cognitive decline similar to childhood dementia. 

In severe cases, Hunter syndrome is life-threatening and patients typically die by age 20. 

Since Oliver’s diagnosis in April 2024, his parents, mother Jingru Chu and father Ricky Chu, have been overwhelmed with hospital visits, just as they had been with Skyler.

"When you find out about Hunter syndrome, the first thing the doctor tells you is 'Don't go on the internet and look it up because you'll find the worst cases and you'll be very, very disheartened.' " Ricky told the BBC. "But, like anybody, you look it up and you're like, 'Oh my goodness, is this what's going to happen to both my sons?' "

But in December 2024, they were able to connect with doctors from the clinical research facility at Royal Manchester Children's Hospital who had developed a “revolutionary” stem cell gene therapy treatment.

“Although it was a big commitment to travel to the UK, of course we want the best for our children,” Ricky said in a statement to the hospital on Monday, Nov. 24. “Due to Skyler’s age, he was not eligible to take part in the Manchester trial and is taking part in a different study in the United States. That has meant splitting up the family, but it was something we were willing to do for Ollie to have the opportunity to be in this trial.”

“There are very few times where your child can have a reset on life so if you can give them that chance, then it’s just something you do,” he added.

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The gene therapy involves removing the patient’s stem cells, sending them to a lab at Great Ormond Street Hospital (GOSH) in London for modification, and replacing the faulty gene by re-injecting the modified cells. 

“We use the machinery from the virus to insert a working copy of the faulty gene into each of the stem cells,” Dr. Karen Buckland of the Cell and Gene Therapy Service at GOSH explained to the BBC. “When those go back to Oliver, they should repopulate his bone marrow and start to produce new white blood cells, and each of these will hopefully start to produce the missing protein [enzyme] in his body.”

In February 2025, Oliver received the genetically modified stem cells with an infusion. He was the first of five boys around the world to undergo the groundbreaking treatment.

The gene therapy was deemed a success. Today, Oliver’s progress has exceeded his doctors’ hopes, and he appears to be developing normally.

“I’ve been waiting 20 years to see a boy like Ollie doing as well as he is, and it’s just so exciting,” researcher Simon Jones, who is co-leading the trial, told the BBC.

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Jingru and Ricky told the hospital that they are in awe of how much better their son is developing and they’re “forever grateful” for being a part of the research.

“Ollie is doing great since having the gene therapy,” Ricky said. “We have seen dramatic improvements, and he continues to grow physically and cognitively. Our hope for Ollie because of this treatment is that he will continue to make his own enzymes and live a normal life without infusions.”

“We’re excited for Ollie’s future,” he continued. “Seeing the difference for Ollie pre-and post-transplant has made us believers."

The parents said that they hope the success will lead to more children being treated, including their other son Skyler.

"Every time we talk about it I want to cry because it's just so amazing," Jingru told the outlet.

"My wish upon the star is for Skyler, to be able to get the same treatment," added Ricky. "It feels like Oliver has got a reset in his life, and I want the same thing for Skyler, even though he's a bit older."