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. It is a relatively common "rare disorder":
approximately 1 in 6000 babies born are affected, and about 1 in
40 people are genetic carriers. Spinal Muscular Atrophy (SMA)
refers to a group of inherited diseases of the motor nerves that
cause muscle weakness and atrophy (wasting). The motor nerves
arise from the spinal cord and control the muscles that are used
for activities such as breathing, crawling, walking, head and
neck control, and swallowing. SMA is a rare disorder occurring
in approximately 8 out of every 100,000 live births, and
affecting approximately 1 out of every 6,000 to 10,000
individuals worldwide. 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, co