A three-year-old boy has astounded doctors with his progress after becoming the first person in the world with his devastating disease to receive a ground-breaking gene therapy.
Oliver Chu has a rare, inherited condition called Hunter syndrome - or MPSII - which causes progressive damage to the body and brain.
In the most severe cases, patients with the disease usually die before the age of 20. The effects are sometimes described as a type of childhood dementia.
Due to a faulty gene, before the treatment Oliver was unable to produce an enzyme crucial for keeping cells healthy.
In a world first, medical staff in Manchester have tried to halt the disease by altering Oliver's cells using gene therapy.
Prof Simon Jones, who is co-leading the trial tells the BBC: "I've been waiting 20 years to see a boy like Ollie doing as well as he is, and it's just so exciting."
At the centre of this remarkable story is Oliver - the first of five boys around the world to receive the treatment - and the Chu family, from California, who have put their faith in the medical team at Royal Manchester Children's Hospital.
A year after starting the treatment, Oliver now appears to be developing normally.
"Every time we talk about it I want to cry because it's just so amazing," says his mother Jingru.
otters_raft in medicine
Hunter syndrome: Boy with rare condition amazes doctors after world-first gene therapy
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