Spinal muscular atrophy (SMA) is a disorder which affects the nerves which control muscle movement (the motor neurons). Due to the motor neurons in the spinal cord not working properly, messages are not sent to the muscles through these motor neurons, causing the muscles to become weak and damaged. This occurs throughout the muscles in the body, including shoulders, hips, and back (most severely affected), muscles used for feeding and swallowing, and muscles used for breathing. Children with SMA type 1 usually die before the age of 2 years old. The other forms of SMA are less severe and lifespans can range.