Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a genetic disease, which causes progressive degeneration of neurons in the spinal cord, leading to weakness and wasting of the voluntary muscles, often most severe in the legs. There are many types of SMA.

One type, Werdnig-Hoffmann disease, is evident before birth or within the first few months of life. The mother may notice a reduction in fetal movement in the final months of pregnancy. Symptoms include floppiness of the limbs and trunk, feeble movements of the arms and legs, swallowing and feeding difficulties, and impaired breathing. The prognosis for this disease is poor.

Type II SMA usually begins between 3 and 15 months of age. Children may have respiratory problems, floppy limbs, decreased or absent deep tendon reflexes, and twitching of arm, leg, or tongue muscles. These children may learn to sit but not stand or walk. Life expectancy varies.

Kugelberg-Welander disease, another form of SMA, appears between 2 and 17 years of age, and causes abnormal walking; difficulty running, climbing steps, or rising from a chair; and slight tremors of the fingers.

Congenital SMA with arthrogryposis is a rare disorder that causes curvature of the spine, chest deformity, severe contractures, an unusually small jaw, and drooping upper eyelids.