should prevent further loss of nerve cells. it's been massive, massive ups and downs, but being able to now have the treatment is just going to be a game—changerfor us and give arthur the best possible life he could have. around one in every 10,000 babies is born with spinal muscular atrophy. what is remarkable is that this one—off treatment may permanently stop any further decline in arthur's muscle function. so how does zolgensma work? it contains a healthy copy of a missing orfaulty gene called smn—i. this is inserted into a harmless virus. in the body, the virus delivers the replacement gene into the nucleus of motor neuron cells. this is essential to prevent those cells from gradually dying. the now healthy motor neuron cells start producing the missing smn protein,