According to FightSMA.org, "Spinal Muscular Atrophy (SMA) refers to a group of diseases which affect the motor neurons of the spinal cord and brain stem. These critically important cells are responsible for supplying electrical and chemical messages to muscle cells. Without the proper input from the motor neurons, muscle cells can not function properly. The muscle cells will, therefore, become much smaller (atrophy) and will produce symptoms of muscle weakness. There are dozens of diseases which affect the motor neuron."

"Degeneration and death of the motor neurons (also called Anterior Horn Cells) in the brain stem and spinal cord produces weakness in the muscles of swallowing, breathing, and limbs. This disease afflicts infants, children, and adults worldwide. It is estimated that spinal muscular atrophy occurs in between one-in-6,000 and one-in-20,000 births. Recent advances in our understanding of the genetics of this disorder confirm that the majority of children and adults afflicted with SMA, have inherited this disorder by receiving one gene from both their mother and their father. This is termed autosomal recessive genetic transmission."

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