A drug that could delay children with a form of muscular dystrophy from needing a wheelchair for up to seven years has been given the green light by a health watchdog.
The National Institute for Health and Care Excellence (Nice) has published new guidance recommending the drug (also called ataluren) for use on the NHS.
A patient access scheme is under negotiation with the manufacturer although Nice said a deal had not yet been finalised with NHS England.
If a deal can be reached, around 50 eligible children in England will be able to take the drug, which slows down progression of the disease and can keep them walking for longer.
Translarna is for patients with a particular type of Duchenne muscular dystrophy, which is one of the most common and severe forms of the disease.
Duchenne usually affects boys in early childhood and is usually fatal by age 30.
Translarna could help around 10 to 15% of those affected by Duchenne in childhood.
The mother of a 10-year-old boy who met David Cameron to ask for the drug has described the news as "life-changing".
Louisa Hill said she was "immensely proud" of her son Archie, who took his fight for the drug Translarna to Downing Street.
Mrs Hill said: "This is amazing, life-changing news. We can't quite believe it, and just want to thank everyone who has supported us. We are immensely proud of Archie.
"Duchenne muscular dystrophy brings so many challenges into his life - and this will become even greater in the future.
"Yet now, for the first time, there is something in our corner. We can have real hope that when, one day, there may be a drug to not only slow down the condition, but completely stop it, our son will be strong enough to benefit."
Nice said Translarna, manufactured by PTC Therapeutics, was approved for children aged five and over.
It said youngsters with the disease typically become wheelchair dependent by the age of 12 and it believed Translarna had the potential to delay the loss of ability to walk.
Research presented to Nice's committee predicted the drug may delay loss of walking for up to seven years.
Nice also heard how some patients were so improved on the drug they could get in and out of bed independently and go to school.
The drug's list price is approximately £220,000 per year per child.
Negotiations are ongoing between the manufacturer and NHS England to agree a cost for the drug. Any agreement would run for five years so more data could be collected. Nice would then review the drug again at the end of this period.
Sir Andrew Dillon, chief executive of Nice, said there were very few treatment options for children with Duchenne caused by a nonsense mutation and described it as a "cruel" disease.
"Because of its very high cost, it is important that details of the financial and other arrangements to enable this new medicine to be offered to patients on the NHS are discussed and agreed between the company and NHS England, and set out in a managed access agreement," he said.
Duchenne muscular dystrophy is a severe progressive disease linked to the X chromosome.
Between 60 and 70 children are born with the disease in England each year.
In around six to nine children, it is caused by a nonsense mutation, which could be helped by the drug.
Last year, Archie, of Gerrards Cross, Buckinghamshire, handed a petition directly to Mr Cameron at 10 Downing Street calling on the NHS to end delays to offering Translarna.
He also had his effort backed by England and Arsenal footballer Jack Wilshere.
The charity Muscular Dystrophy UK said families had waited almost 18 months for a decision on the drug.
Robert Meadowcroft, chief executive of Muscular Dystrophy UK, said: "Parents of children eligible for Translarna have fought courageously for this outcome, and to give their children the chance to keep walking for longer.
"This announcement comes as wonderful news and a true victory for the families."
He said a managed access agreement would "allow us to gain a clearer picture of the full potential of Translarna, and, crucially, to buy precious time for other promising potential treatments to reach licensing stage. It is a chance to transform childhoods.
"However, we are concerned now that it could takes months for NHS England to implement the agreement and get the drug to clinic."
An NHS England spokesman said: "Nice's decision recognises that there is still uncertainty over the benefits of ataluren, so it should only be offered on the NHS with further substantial discount and with the ability to stop funding if evidence shows it's not as effective as claimed.
"It is now for the manufacturer to agree to terms which allow us to make ataluren available without a disproportionate impact on our ability to fund new treatments for other patients."