That little Sidney Cooke is alive today is thanks to a dose of a new wonder drug labelled "the most expensive drug in the world".

Sidney, from Yalding near Maidstone, was born with type one spinal muscular atrophy (SMA), a muscle-wasting disease that in the past meant sufferers seldom reached their second birthday.

But in March 2021, the NHS announced it had reached a deal with the American manufacturers of the gene therapy drug Zolgensma, to make it available in Britain.

The NHS will not reveal exactly how much it is paying for the treatment, but in America, it was retailing at the equivalent of £1.8m a dose.

Sidney was only the 12th child in the UK to receive the drug on the NHS.

SMA is a rare genetic condition that affects only around one in every 6,000 babies.

The typical symptoms are that the baby is floppy and doesn't achieve the normal developmental growth stages of sitting up and then walking. Later they develop problems breathing and swallowing.

Sidney's mum Sophie Cooke, 34, said: "After three months, I had a beautiful blue-eyed smiling boy - but he couldn't hold his head up and barely moved."

That she noticed his problems early was enormously helpful to Sidney's chances. The trouble is a fault in the child's DNA which means normal muscle growth is not triggered. One shot of Zolgensma effectively replaces the damaged gene and tricks the body into action.

Unfortunately, although it stops any further deterioration of the muscles it cannot cure the damage already done and Sidney is now using a wheelchair.

Mrs Cooke said: "The Zolgensma saved Sidney's life, but now, no doubt because of the expense, the NHS seem to feel they have done their bit."

There are two other experimental drugs on the market which work in a slightly different way to Zolgensma, but which seem to have some restorative effect. They are cheaper, but still cost around £250,000 a shot, and a course of treatment is needed.

They work on the body's "back-up" growth gene

But Mrs Cooke said: "We can't get either on the NHS."

They have however, managed to get Sidney into a clinical trial for one of the drugs, Sprinraza with a pharmaceutical company in Barcelona.

It means the family have to fly repeatedly to Spain for treatment.

Mrs Cooke said: "We are throwing everything we can at Sidney's treatment. All the therapies and treatments we can access, because they are most likely to be effective while he is young."

"I liken it to going on a long car journey in a hybrid car, when you set off you would want to make sure you have a full tank and a fully charged battery."

But Sidney's treatment is taking a huge toll on the family, both financially and in the sacrifices they have to make.

Mrs Cooke said: "I used to be the main earner, working full-time as a PA at the Shard. Now I'm an at-home carer and I've had to give up work.

"My husband, Aden, is a gas engineer. He's still working but of course he's had to take a lot of time off. When Sidney first had his treatment, his immune syndrome was depressed so we all had to isolate for months."

The couple have another child, daughter Nancy aged four.

Mrs Cooke said: "She shows no signs of having SMA and in fact when she was a baby she hit all her development milestones ahead of time."

However, people can be carriers of the defective gene, without exhibiting symptoms themselves.

Mr Cooke said: "It turns out that both myself and my husband are carriers, though we didn't know that. We are both the youngest in our families and there have been no incidences of SMA before that we are aware of."

It is possible that Nancy too will carry the defective gene that could give her own children a roughly one in four chance of developing the condition.

The family are waiting until she is older before having her tested.

Mrs Cooke said: "People say the condition is rare, but it's really not that rare. It's just that not many people have heard of it because before babies with SMA did not survive very long."

Mrs Cooke was critical of the Government in taking so long to approve the life-saving treatment. She said: "Zolgensam had already been used in America for seven years."

Though she admitted, whether the drug would have the life-long effect claimed for it, was still unknown.

She said: "We only know as much about it as the eldest child who has been treated.

"We have to be positive and have learnt to live with a lot of uncertainty."

She was also critical that there was no automatic SMA screening of new-born babies.

She said: "If a child is given the drug before any symptoms appear, they can avoid damage.

"But once symptoms appear, their bodies degenerate very quickly."

Fortunately the care that Sidney is receiving seems to be doing some good.

He can now do some supported standing, though he still needs to be attached to a ventilator at night to sleep.

The family have only been able to afford his specialist care and equipment because of the generosity of well-wishers.

Family and friends have run a series of fundraising events, including football matches, sports days and even a nude Calendar Girls fundraiser in her parents' home village of Smarden.

Mrs Cooke said: "Everything is so expensive. If we find any bit of kit that's less than £1,000 now we think it's a bargain.

"We couldn't have helped Sidney like this without support from so many kind people.

The latest to come to their aid is family friend Adam Bevis, 37, from Orpington who will be running the Brighton Marathon tomorrow (Sunday) to raise funds for the family.

He said: "I have always wanted to push myself and run a marathon.

"Training has been tough as I have two young children myself, who aren’t the best sleepers!

"However, I’m delighted to be able to help raise funds to get Sid the equipment he needs to help make his mobility as best as possible.

"His little face will help get me through when the run starts to get tough."

Sidney will turn two on April 14.

His mum said: "He is already turning into a terrible two-year-old, getting very bossy and frustrated when he can't do things.

"He's started to realise that he is different from other children."

The Cooke family are being supported by the Tonbridge-based children’s charity Tree of Hope.

To sponsor Mr Bevis on his marathon run or to donate to Sidney’s fund, visit the charity here.

You can follow Sidney's progress on Instagram here.

Mrs Cooke said: "Sidney is coming on in leaps and bounds. He loves animals and can’t wait to go to nursery, but his continued progress relies on our being able to fund the equipment and therapies to enable it."