Spinal muscular atrophy is a group of inherited disorders that cause progressive muscle degeneration and weakness. Spinal muscular atrophy (SMA) is the second leading cause of neuromuscular disease. It is usually inherited as an autosomal recessive trait (a person must get the defective gene from both parents to be affected).

There are several types of SMA called subtypes. Each of the subtypes is based on the severity of the disorder and the age at which symptoms begin. There are three types of SMA that affect children before the age of 1 year. There are two types of SMA, type IV and Finkel type, that occur in adulthood, usually after age 30. Symptoms of adult-onset spinal muscular atrophy are usually mild to moderate and include muscle weakness, tremor and twitching.

The prognosis for individuals with SMA varies depending on the type of SMA and the degree of respiratory function. The patient’s condition tends to deteriorate over time, depending on the severity of the symptoms.

Spinal muscular atrophy affects 1 in 6,000 to 1 in 10,000 people.