Zolgensma delivers a new, working gene into the body which mimics SMN1, the gene that is reduced, missing or faulty in people with SMA. The gene is delivered to the motor neurons by a viral vector called AAV9, which is a virus that is not harmful or known to make people sick but instead has been modified to be used for transporting. To make the vector, the DNA of the virus is removed so that the new SMN gene can be put inside. 

Once the gene reaches the motor neuron, it helps the body produce enough SMN protein. The increased amount of SMN protein available to motor neurons can help slow or stop the muscle weakness and wasting in people with SMA from getting worse. Given this, it is important treatment is started as early as possible.