Symtoms+of+SMA

The purpose of the SMN protein is to maintain motor neurons, which are key in normal muscle movement of the neck and spine. The mutation that causes SMA (see: SMA-Why Does it Happen? and Functions of the SMN Protein) lowers the production of SMN. Without SMN, less motor neurons can be maintained. Because the motor neurons control muscle movement, when there are less of them, the muscles grow weak and it is difficult for an individual to use them without the help of motor neurons. The motor neurons themselves are located in the spine and brainstem. It is for this reason that individuals who have SMA seem "floppy." They often have trouble sitting, lifting their head, turning their neck about, and, in some cases, swallowing and breathing. The muscles used for these actions are to weak, causing individuals to often need help crawling, sitting, and walking. (Spinal Muscular Atrophy)