SMA is an inherited neuron disease that affects the central nervous system and skeletal musculature. SMA (Spinal Muscular Atrophy) affects motor nerve cells in the spinal cord, destroying their basic abilities such as walking, eating and breathing. It is the number one genetic cause of death for babies. It is an uncommon disease that causes muscle wasting and weakness. There are four different types of SMA disease. This classification represents the age at which the disease begins and the diseases it can cause. The older the age at which SMA shows its symptoms, the milder the disease.