The boy receiving treatment.University of Manchester
A three-year-old Oliver (Ollie) Chu has become the world’s first patient to receive a revolutionary stem cell gene therapy for Hunter syndrome.
This rare, progressive, inherited disorder damages the body and brain, with effects often likened to a form of childhood dementia. The condition is life-threatening, with a typical life expectancy between 10 and 20 years.
Developed over 10 years at the University of Manchester and tested at the Royal Manchester Children’s Hospital (RMCH), the therapy is a one-off procedure.
The boy received the gene therapy in February 2025. Several months post-procedure, Ollie has made a full recovery from the transplant.
“Gene therapy is not only safer and more effective, but it enables us to use the child’s own cells, which cuts out the need to find a donor, and means we can produce more enzyme for the patient,” said Professor Rob Wynn, Consultant Paediatric Haematologist and Director of Paediatric Bone Marrow Transplant Programme at RMCH and joint clinical lead.
Gene therapy treatment
Also known as mucopolysaccharidosis type II (MPS II), this syndrome is caused by a faulty gene that prevents the body from producing a vital enzyme.
Without this enzyme, complex sugar molecules (mucopolysaccharides) start to form in organs and tissues. This leads to progressive damage, including joint stiffness, hearing loss, heart/breathing issues, developmental delays, and cognitive decline (childhood dementia).
At present, the licensed treatment is a costly (£375,000 per year), weekly, lifelong Enzyme Replacement Therapy (ERT) called Elaprase.
Elaprase can help manage physical and organ problems, but cannot treat or improve mental decline because it is inefficient at crossing the blood-brain barrier.
In this clinical study, the experts use a one-off gene therapy treatment that involves taking the child’s stem cells, correcting the faulty gene in a laboratory, and then re-injecting the modified cells back into the patient.
Notably, these modified stem cells can produce high levels of the missing enzyme. Moreover, the treatment reaches the brain to break down the toxic sugar build-up, which could hopefully prevent dementia-like decline.
“Since having the gene therapy Ollie is no longer having weekly Elaprase infusions, but instead of seeing levels of the previously missing enzyme dropping we are seeing very high levels in his blood, and this is an extremely encouraging sign that the treatment is working,” said Professor Simon Jones, Consultant in Paediatric Inherited Metabolic Disease at the Manchester Centre for Genomic Medicine at Saint Mary’s Hospital.
First of five children
The therapy has been initiated with California-resident Ollie, who is the first of five children with Hunter syndrome participating in the trial.
His older brother, Skyler, also has Hunter syndrome but was not eligible for this specific trial due to his age.
“Ollie is doing great since having the gene therapy. 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,” said Ricky Chu, Ollie’s father.
“We’re excited for Ollie’s future. Seeing the difference for Ollie pre-and post-transplant has made us believers,” he added.
The researchers highlighted that the success of this blood cell gene therapy approach offers an exciting blueprint for treating many other genetic conditions.