Spinal muscular atrophy (SMA) is a genetic disease affecting the part of the nervous system that controls voluntary muscle movement. Most of the nerve cells that control muscles are located in the spinal cord, which accounts for the word spinal in the name of the disease.
SMA is muscular, because its primary effect is on muscles, which don’t receive signals from these nerve cells. Atrophy is the medical term for wasting or shrinkage, which is what generally happens to muscles when they’re not active. SMA involves the loss of nerve cells called motor neurons in the spinal cord and is classified as a motor neuron disease. There’s a great deal of variation in the scope and severity of SMA in different people.
More information on Spinal Muscular Atrophy (SMA)
With thanks to MDNSW