Spinal Muscular Atrophy (SMA) is a motor neuron disease. The motor neurons affect the voluntary muscles that are used for activities such as crawling, walking, head and neck control, and swallowing. Approximately 1 in 6000 babies born are affected, and about 1 in 40 people are genetic carriers.
SMA affects muscles throughout the body. In the most common types, weakness in the legs is generally greater than in the arms. Sometimes feeding, swallowing, and respiratory function (e.g., breathing, coughing, and clearing secretions) can be affected. When the muscles used for breathing and coughing are affected and weakened, this can lead to an increased risk for pneumonia and other respiratory infections, as well as breathing difficulty during sleep. The brain’s cognitive functions and the ability to feel objects and pain are not affected. People with SMA are generally grouped into one of four types (I, II, III, IV) based on their highest level of motor function or ability.