Four-year-old Hunter Payne enjoys running around and playing like any other boy his age.

But a diagnosis of Duchenne Muscular Dystrophy means instead instead of growing stronger, Hunter could need a wheelchair by the age of 12.

The rare but debilitating genetic condition mostly affects boys and causes rapid muscle weakness.

But a world-first international medical trial is offering hope for children like Hunter, who is one of just ten young boys taking part globally.

Hunter is one of three boys in NSW to be among the first to receive the experimental gene replacement therapy.

Michelle Lorentzos, who is leading the clinical trials at The Children's Hospital at Westmead, says if successful, it could change the way the disease is treated.

"We think by treating the boys earlier, we may be able to prevent much of the weakness and disability that has already occurred in older patients," Dr Lorentzos said on Wednesday.

"(This is) a transformative intervention that may enable the boys to continue walking into adulthood and also improve their life expectancy."

Current treatment for muscular dystrophy involves high-doses of steroids, which can result in some improvement but is also associated with significant side effects.

The trial is using a benign virus to target muscular dystrophy at its root cause, delivering a healthy gene to replace the faulty or mutated one.

Hunter's mother Maddison Elphick says her son hasn't experienced any side effects.

"The trial's been amazing for us," she said.

"He's just up and moving and doing things that four-year-olds with this condition can't do."

Premier Chris Minns met Hunter and other trial participants at Westmead on Wednesday, saying the Sydney Children's Hospitals Network has the pediatric expertise to offer world-leading care.

"I'm very proud that NSW is a part of the world trial for this debilitating disease," Mr Minns said

"This new gene therapy represents a beacon of hope for these three young boys and their families."