Three-year-old Oliver Chu has Hunter Syndrome. It's a devastating life-limiting disease and currently has no cure.

But little Oliver is the first person in the world to receive a groundbreaking gene therapy that scientists hope will save his life.

Hunter Syndrome is a rare, inherited condition which causes progressive damage to the body and brain.

Due to a faulty gene, patients are unable to produce an enzyme vital for keeping cells healthy.

In severe cases, those with the disease usually die before the age of 20.

In a world first, medical staff in Manchester, UK, have tried to halt the disease, by altering Oliver's cells using gene therapy.

The Chu family, from California, USA, were overwhelmed when they found out Oliver qualified for the trial.

"We went home and just waited, and waited, and waited to see if we could be approved for this trial. And when we got the news, we just cried. Because with Hunters, there's no real treatment," says Ricky Chu, Oliver's dad.

Sadly, Oliver's older brother also has the genetic condition.

But, nearly a year after starting the treatment, Oliver has astounded doctors at Manchester Children's Hospital and appears to be developing normally.

"When the kids were born, I always knew they would make a difference in the world. Him being the first, even though it wasn't his choice, I feel like he's a superhero in his own right, because if he paves the way for other kids to get the same treatment and to be healthy and live normal lives, it's his super power," says Ricky Chu.

The new therapy removes stem cells from the patient's blood.

A working version of the faulty gene is then inserted.

The altered stem cells are then put back into the patient, creating white blood cells which reproduce the working gene around the body.

Professor Simon Jones, who is co-leading the trial, is delighted by Oliver's progress.

"We work on a study like this and prepare for this sort of day for 15 years, and you don't know what the outcome is going to be. That's why these are trials. And you prepare the best possible treatment you can do, but the reality is you don't know," he says.

For Oliver and the rest of the Chu family, the future is filled with hope.