Spinal muscular atrophy is a genetic disorder that affects the control of muscle movement. It is caused by a loss of specific nerve cells called motor neurons in the spinal cord and the part of the brain that is connected to the spinal cord. The loss of motor neurons leads to weakness and deteriorating of muscles used for a wide range of activities from crawling and walking, to sitting up, and controlling head movement. In severe cases of spinal muscular atrophy, the muscles used for respiratory and digestive functions are affected. There are many types of spinal muscular atrophy distinguished by the arrangement of features, severity of muscle weakness, and age when the muscle problems
