Patients with the devastating genetic condition, spinal muscular atrophy (SMA), could gain access to vital treatment earlier than expected, but charities are warning that some patients could still lose the ability to move, breathe or swallow before it is implemented.
Around 1,300 children and adults are living with the devastating effects of SMA in the UK.
Each year, more than 40 babies are born with the most severe SMA Type 1, but without access to the drug Spinraza, life expectancy is rarely longer than two years.
Some children who have received Spinraza have seen their muscle strength improve and have already lived long enough to crawl and even walk.
A proposed interim scheme from the National Institute for Health and Care Excellence (Nice), NHS England and pharmaceutical company Biogen has been welcomed by charities including Muscular Dystrophy UK, SMA Support UK, the SMA Trust and TreatSMA, which are urging those involved to put it into effect as quickly as possible.
They are also calling for Nice's current system for approving rare disease drugs to be overhauled so that patients can get faster access to treatments.
Robert Meadowcroft, chief executive of Muscular Dystrophy UK, said: "While we wait for the interim scheme to be implemented, the clock ticks away for those affected by this devastating, life-limiting condition who desperately need access to this treatment.
"An interim scheme, which looks at making Spinraza available in the short term, is welcome. We must, however, address the problems with the current system for approving rare disease drugs.
"A longer-term solution needs to be found. We need a more appropriate assessment route for rare disease drugs like Spinraza, which fall between Nice's appraisal routes for new treatments."
Liz Lockley, 35, said the drug could enable her son George, six, who has SMA Type 2, to maintain some of the strength he has left.
Ms Lockley, from Welwyn Garden City, Hertfordshire, said: "SMA is a cruel condition. As a parent, it's heart-breaking to see your child gradually lose their physical abilities, particularly when it happens in parallel to their twin brother gaining new skills every day.
"While Spinraza is not a cure, it could help George maintain some of the strength he has left and could potentially enable him to gain new skills. Even if Spinraza could give George the ability to cough effectively, the SMA would no longer be such a threat to his life.
"Simple things like having more arm strength could enable George to live a much more independent life. This would be invaluable to us and, more importantly, to George."
Spinraza proved so effective in a clinical trial for children with SMA Type 1 that the trial was stopped early so that children could potentially access it.
Treatment is now being delivered to some children with SMA Type 1 via a special compassionate access scheme, but the charities said not all can access it.
SMA causes progressive muscular weakness and loss of movement due to muscle wasting (atrophy). This may affect crawling and walking ability, arm, hand, head and neck movement, breathing and swallowing.