Spinal Muscular Atrophy

A group of hereditary diseases that are characterized by weakness and wasting of the voluntary muscles in the arms and legs of infants and children. The disorders are caused by the loss of motor neurons in the spinal cord. The type of SMA (I, II, or III) is determined by the age of onset and the severity of symptoms. Type I (also known as Werdnig-Hoffman disease, or infantile-onset SMA) is evident at birth or within the first few months. Symptoms include floppy limbs and trunk, feeble movements of the arms and legs, swallowing difficulties, a weak sucking reflex, and impaired breathing. Type II (also known as juvenile SMA, intermediate SMA, or chronic SMA), has an onset between 6 and 18 months. Legs tend to be more impaired than arms. Children with Type II are usually able to sit without support if placed in position. Some may be able to stand or walk with help. Type III (also called Wolhlfart-Kugelberg-Welander disease, or mild SMA) can begin as early as the toddler years or as late as adolescence. Children can stand alone and walk, but may have difficulty getting up from a sitting position. There is also a less common Type IV form of the disease that affects adults and is characterized by a slower progression of symptoms that particularly affect walking. Symptoms typically emerge after age 35. There is no cure for SMA. Treatment consists of managing the symptoms and preventing complications.