The nation's leading supporter of biomedical research on disorders of the brain and nervous system. The disorder causes weakness and atrophy of the voluntary muscles.
Weakness is often more severe in the legs than in the arms.
SMA type I , also called Werdnig-Hoffmann disease , is evident in utero or within the first few months of life. There may be a paucity of fetal movement in the final months of pregnancy. Affected children never sit or stand and usually die before the age of 2. II usually begin between 3 and 15 months of age. These children may learn to sit but do not stand.