The mother of a 10-year-old boy who met David Cameron to ask for a muscular dystrophy drug has described news it will be funded on the NHS 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.
The National Institute for Health and Care Excellence (Nice) has published new guidance recommending the drug (also called ataluren) after a patient access scheme was agreed with the manufacturer.
It means around 50 eligible children in England will be able to take the drug, which slows down progression of the disease and can help 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. They generally only live into their 20s or 30s.
Translarna could help around 10 to 15% of those affected by Duchenne in childhood.
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."
Last year, Archie, of Gerrards Cross, Buckinghamshire, had his wish come true when he handed a petition in person to Mr Cameron.
The Prime Minister surprised Archie and his family outside 10 Downing Street as they handed in the 22,785 signature petition calling on the NHS to end delays to offering Translarna.
Archie, who was diagnosed with the severe and progressive Duchenne at the age of three, also had his effort backed by England and Arsenal footballer Jack Wilshere.
The charity Muscular Dystrophy UK said the families of just over 50 eligible children in England - or 60 across the UK - have waited almost 18 months for a decision on the drug.
It said some youngsters may have lost the ability to walk during this time, meaning they will no longer meet the Nice criteria of being aged over five and still able to walk.
Those who do get the drug will be able to have it for five years, during which time they will be closely monitored and have their progress recorded.
Nice will then review the drug after five years.
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.
"A managed access agreement means that within a matter of months, NHS England will be supplying eligible children with the first genetic therapy available to treat the condition.
"Such an agreement will 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. Having waited 18 months for a decision, this is a delay boys and their families can ill afford.
"We call on NHS England to act with the urgency and resolve that these children and their families deserve."
In 2014, Translarna became the first genetic therapy for Duchenne muscular dystrophy to be approved within the EU. It is available in several other European countries.
Earlier this week, the Scottish Medicines Consortium (SMC) said it would not approve the drug for use in Scotland.