November 25, 2025: In a remarkable medical breakthrough, three-year-old Oliver Chu, son of Ricky and Jingru from California has become the first person in the world to receive a pioneering gene therapy for Hunter syndrome, offering new hope for families affected by this devastating inherited condition.
Oliver was the first of five boys around the world to receive the treatment.
Hunter syndrome, also known as MPS2 (mucopolysaccharidosis type 2), is a rare genetic lysosomal storage disorder that predominantly affects males. The condition occurs due to the deficiency of crucial enzyme called iduronate-2-sulfatase (IDS), which is responsible for breaking down large sugar molecules known as glycosaminoglycans. 1
Without this enzyme, harmful chemicals accumulate in multiple organs of the body.
The estimated incidence is approximately 1 in 162,000 live male births. 1
Hunter syndrome follows an X-linked recessive inheritance pattern. Because boys have only one X chromosome and therefore a single copy of the IDS gene, they are primarily affected by the condition.
Carrier mothers can transmit the malfunctioning IDS gene to 50% of their sons, who will then develop the disease.
While extremely rare, a few sporadic cases have been reported in carrier females due to the chromosomal rearrangement or inactivation of the normal gene expressing the X-chromosome. 1
Children with Hunter syndrome typically appear healthy at birth and develop normally for the first few years of life. Symptoms usually begin to manifest between ages 3 and 4, when parents may notice behavioral changes, attention difficulties, speech delays, cognitive decline, and poor school performance. 1
The condition was first identified in 1917 by Canadian physician Charles Hunter, who documented the disease in two brothers from the same family.
The symptoms of Hunter syndrome are progressive and affect multiple body systems:
Physical Characteristics:
Coarse facial features (thick lips, broad nose, flared nostrils)
Large head with protruding tongue (macroglossia)
Short stature
Pebbly skin rash, typically over the shoulder blades
Skeletal Issues:
Spinal deformities
Thickening of long bones
Respiratory Problems:
Frequent upper respiratory infections
Hoarse voice
Obstructive sleep apnea due to enlarged tonsils, blocked nasal passages, and narrow airways
Organ Involvement:
Enlarged liver and spleen causing abdominal distension
Heart complications leading to high blood pressure and potential heart failure
Recurrent ear infections and hearing loss
Neurological Symptoms:
Delayed development and intellectual disability
Behavioral problems
Loss of previously attained developmental milestones
Seizures
Life expectancy varies significantly depending on disease severity. According to medical data, individuals with severe Hunter syndrome and brain involvement typically do not survive beyond their second decade of life.
Those with milder forms of the disease may live up to their sixth decade.
Before Oliver's groundbreaking therapy, only medicine available was: Elaprase, prescription medicine for Hunter’s syndrome that costs approximately £300,000 per patient per year.
Elaprase has a critical limitation: it cannot cross the blood-brain barrier. This means it does nothing for the cognitive symptoms.
Then came an unexpected opportunity. Researchers at the National Institute for Health and Care Research (NIHR) Royal Manchester Children's Hospital met Oliver and his dad Ricky in December 2024.
Oliver was diagnosed with Hunter Syndrome in April 2024.
On that day, Oliver was hooked up to a machine and had some of his cells removed, that became the first crucial step in trying to halt his genetic disorder.
"His blood is being passed through a fancy machine that is collecting a specific type of cell called stem cells which will be sent to a lab to be modified and then given back to him," explained Dr. Claire Horgan, consultant pediatric hematologist explained to BBC.
Oliver’s cells were carefully packed and sent to the laboratory of Great Ormond Street Hospital (GOSH) in London.
Dr. Karen Buckland, from the Cell and Gene Therapy Service at GOSH and UCL senior research fellow, explained: "We use the machinery from the virus to insert a working copy of the faulty gene into each of the stem cells."
Doctors collected Oliver’s own stem cells (the “mother cells” that make all blood cells) from his blood.
In a London lab, they used a harmless virus as a delivery van to insert a healthy copy of the missing IDS gene into these stem cells. The inserted gene is also modified so that the enzyme it produces can cross the blood-brain barrier (BBB).
The corrected stem cells were frozen and dripped back into Oliver through simple infusions.
These new stem cells produce white blood cells, which produce the missing enzyme and deliver it around the body.
Each of these cells carries the working gene and would produce the missing enzyme in his body.
That time, Oliver was accompanied by his mother Jingru to the clinical research facility at Royal Manchester Children's Hospital.
A member of the research team opened a large metal cryopreservation tank. Inside, frozen at extreme temperatures, were Oliver's genetically modified stem cells, transported back from London.
A small, clear infusion bag was carefully removed and slowly brought to body temperature in a tray of liquid. After multiple safety checks, a nurse drew the clear fluid, containing approximately 125 million gene-modified stem cells into a syringe.
The infusion took about 10 minutes. An hour later, a second identical infusion was administered.
In just over two hours, the gene therapy was complete.
After a couple of days, Oliver and Jingru flew back to California.
Three months later, the Chu family returned to Manchester for crucial follow-up tests.
Then came the news that seemed almost too good to be true: Oliver had been able to stop his weekly enzyme infusions entirely. His body was now making its own enzymes.
"I want to pinch myself every time I tell people that Oliver is making his own enzymes," Jingru told BBC News, her voice filled with emotion. "Every time we talk about it I want to cry because it's just so amazing."
Skyler, the five-year-old brother of Oliver was protective and caring toward him, delighting in the world around him despite his own challenges with delayed speech and motor skills. Skyler, also suffering from Hunter Syndrome continues to receive infusion therapy that helps his body but cannot reach his brain.
Initially, doctors thought Oliver might be too old for the trial, as the treatment cannot reverse existing damage. But tests showed he was still largely unaffected.
By late August, Oliver was nine months post-treatment, and follow-up tests provided definitive confirmation: the gene therapy was working spectacularly.
This medical triumph nearly didn't occur. Behind Oliver's success lies a story of scientific perseverance and last-minute rescue.
Researchers at the University of Manchester, led by Professor Brian Bigger, had spent more than 15 years developing the gene therapy for Hunter syndrome. In 2020, the university announced a partnership with Avrobio, a small US biotech company, to conduct a clinical trial.
For three years, preparation continued. Then disaster struck: Avrobio handed the license back to the university following poor results from another gene therapy study and a lack of funds. The first-in-human trial was in jeopardy before it had even begun.
In a crucial intervention, British medical research charity LifeArc stepped in, providing £2.5 million in funding to save the trial.
Without this eleventh-hour rescue, Oliver and other families would have lost their chance.
1. Hashmi MS, Gupta V. Mucopolysaccharidosis Type II. [Updated 2023 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK560829/
(Rh/VK)
