What Is Spinal Muscular Atrophy?

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by the loss of motor neurons, the nerve cells that control muscle movement. It is caused by a mutation in the SMN1 gene, which leads to a deficiency in the production of the survival motor neuron (SMN) protein. SMN is essential for the survival of motor neurons, and its deficiency leads to the progressive degeneration of these cells.

SMA is classified into different types based on the age of onset and the severity of symptoms. The most common type is SMA type 1, also known as infantile SMA, which typically manifests in infants before 6 months of age. Infants with SMA type 1 have severe muscle weakness and difficulty breathing and swallowing. They may also experience respiratory failure and death in early childhood.

SMA type 2, also known as intermediate SMA, usually develops in children between 6 and 18 months of age. Children with SMA type 2 have less severe muscle weakness compared to SMA type 1, and they may be able to sit or stand but are unable to walk.

SMA type 3, known as juvenile SMA, develops later in childhood or adolescence. Individuals with SMA type 3 may have mild to moderate muscle weakness and can usually walk but may have difficulty running or climbing stairs.

Treatment options for SMA include medications, such as nusinersen (Spinraza) and risdiplam (Evrysdi), that can increase the production of SMN protein. Physical therapy and other supportive measures are also important in managing the symptoms of SMA.