A five-year-old boy who received the world’s most expensive drug as a baby has made “incredible progress” and can walk independently, his mother said.

Edward, from Colchester, has spinal muscular atrophy (SMA) which means he lacks a protein vital for muscle development.

He was one of the first children in England to be given the gene therapy Zolgensma, which costs £1.79m for the one-off treatment, through the NHS in 2021.

Mother Megan said Edward was her “pride and joy” and he had achieved milestones she never thought possible.

About 65 babies are born with SMA in England each year. It causes muscle weakness and affects movement and breathing, meaning most babies do not live past the age of two without intervention.

Megan said Edward had gone from being lethargic as a baby to a cheeky, playful boy, who was “full of life” and “a real character”.

He might need to use a wheelchair for the rest of his life, but she added: “It does not matter, as long as he is happy. We are so proud of him.”

“Edward had to have a double hip replacement in October and he’s only just getting back on his feet, but in general he is doing so well.

“He is learning to swim, he can float on his own, which is really hard for children with SMA because they don’t have natural buoyancy.

“This summer, he jumped off a boat into the sea and he went on a jet ski. He’s a very sweet, loveable little guy.”

Edward has just started school, where he has made lots of friends, and “does everything an ordinary five-year-old boy does”.

“We just didn’t think that was possible. We didn’t know what quality of life he would have,” she said.

Various doctors and medical professionals visited him whenever he was in hospital, even when they were not treating him, because they were amazed by his progress, she added.

“They want to see first-hand what gene therapy has done for him.”

The family moved to London so Edward can have physiotherapy up to five times a week.

Ms Willis gave up her job in event management to care full-time for Edward.

It was not certain he would receive the drug on the NHS, so she started a fundraising campaign, and has used the money to pay for specialist physio and equipment, to which she credits his progress.

“We raised £170,000 over five years but that money has nearly gone. It’s been put to a lot of good use,” she said.

“It has saved us as a family, not having to worry about the money. We’re fundraising again now because all of the progress he has made has been due to private care.”

Zolgensma is thought to be the most expensive drug in the world, though NHS England said it had negotiated an undisclosed discount on its £1.79m list price.

Edward, who was diagnosed at two months old, was receiving another drug called Spinraza, which involves regular spinal regular injections for life, compared to a one-off injection of Zolgensma.

Because it is such a new drug, long-term outcomes are not known, but Megan said she believed this generation of babies with SMA would be the first to reach adulthood.

Prof James Palmer, medical director for specialised commissioning at NHS England, said: “It is a huge pleasure to see the remarkable benefits that this innovative gene therapy has provided for Edward since he was treated four years ago.

“Edward is one of more than 150 children with SMA to benefit from this one-shot treatment which has had a huge impact on their lives, and I’m optimistic that many more conditions like SMA will also become treatable over the coming years as medical advances continue at pace.”