Spinal muscular atrophy (SMA) is a progressive, lethal disease that gets worse over time. Patients with the disease lack a gene that produces a protein called ‘survival motor neuron’ (SMN) protein, which is essential for the normal functioning and survival of motor neurons (nerves from the brain and spinal cord that control muscle movements). Without this protein, the motor neurons deteriorate and eventually die. SMA is divided into 4 subtypes, based on when the disease starts and how severe it is. SMA is an inherited disease and is usually diagnosed within the first few months of life for the most severe subtype (type 1). SMA causes the muscles to fall into disuse, leading to muscle wasting (atrophy) and weakness, and in its most common form (SMA type 1), loss of swallowing function, breathing failure and (absent treatment) death within the first few years of life.
AVXS-101 is a gene replacement therapy, made of a virus that has been modified to contain the primary gene for the SMN protein, which is lacking (or mutated) in patients with SMA. When injected into the patient, the virus is expected to carry the gene into the nerve cells, enabling them to start producing sufficient amounts of SMN. This is expected to improve the survival and function of the motor neurons, and so preserve muscle function. AVXS-101 is thought to address the root cause of SMA and therefore, if licensed, may offer an additional treatment option for patients with spinal muscular atrophy.