Groundbreaking gene therapy gives hope to kids with Hunter syndrome

A three-year-old boy from California has become the first patient with Hunter syndrome to receive an experimental gene therapy developed in Manchester, marking a potential advance for treating the rare and progressively disabling disorder.

Hunter syndrome mostly affects boys and causes the body to slowly fill up with substances it cannot break down, says the BBC.

Normally, the body uses special enzymes-like tiny cleaning tools-to get rid of certain waste materials inside cells. In Hunter syndrome, one of those enzymes (called IDS) is missing because of a faulty gene. Without that enzyme, large sugar-like molecules build up in different parts of the body.

Over time, this buildup causes a range of problems, including:

• Changes in facial features
• Shorter height than expected
• Stiff joints
• Hearing loss
• Heart and breathing issues
• Learning difficulties, because the buildup can also affect the brain

Children with Hunter syndrome are usually born looking healthy. Most start showing signs around age two, and the symptoms gradually get worse.

Oliver Chu was treated as part of a clinical trial co-led by Prof Simon Jones at Royal Manchester Children's Hospital. His older brother, Skyler, also has the condition. The trial uses a one-time infusion of gene-modified stem cells intended to replace the missing enzyme and reach the brain.

The project was nearly halted in 2023 after partner biotech company Avrobio returned the licence, citing financial constraints and results from another study. The British medical research charity LifeArc provided £2.5 million to keep the programme running.

Oliver underwent stem cell collection in Manchester in December 2024. The cells were sent to a laboratory at Great Ormond Street Hospital in London, where researchers inserted a functional IDS gene using a modified virus. The gene was adapted to produce an enzyme capable of crossing the blood–brain barrier. In February 2025, Oliver received two infusions containing around 125 million modified stem cells.

Doctors reported early signs of improvement by May 2025, three months after treatment. Oliver's parents said he appeared more mobile and communicative, and his weekly enzyme infusions were halted after tests showed he was producing his own enzymes. By August, nine months after the procedure, clinicians said checks confirmed sustained enzyme production. Prof Jones said Oliver, who previously produced none, was now generating "hundreds of times the normal amount."

According to clinicians, Oliver's development a year after treatment appears consistent with children who do not have the condition, with improvements noted in speech, agility and cognitive skills.

Oliver is the first of five boys from outside the UK to receive the therapy. All participants will be monitored for at least two years. Researchers are applying the same approach to other metabolic disorders, including MPS I (Hurler syndrome) and MPS III (Sanfilippo syndrome).

Oliver's parents said they are "eternally grateful" and hope the treatment will eventually be made available to their older son.