Spinal muscular atrophy (SMA) is a genetic condition that results in weakened muscles and difficulties with movement. There are several different types of SMA, but the most common - and most severe - is type 1, which manifests during the first six months of a child's life. The condition progresses (gets worse) over time, and babies with type 1 spinal muscular atrophy rarely live longer than two years.

But a gene therapy called Zolgensma may be able to change that. Zolgensma is manufactured by Novartis Gene Therapies, an American biotechnology company, and while the list price is almost £1.8 million, the NHS has negotiated an undisclosed discount and infants in the UK can now receive this potentially life-saving treatment for free.

Yesterday, it was reported that a baby boy from London had become the first patient in the UK to receive this treatment. "Baby Arthur is just five months old," wrote the BBC's medical editor Fergus Walsh. "He has no way of knowing the treatment he is receiving in his right arm is the world's most costly medicine."

SEE ALSO: What is Gene Therapy?