In this autoimmune disease, the body attacks its own nervous system, destroying the myelin sheath that protects the nerve cells. This prevents the nerves from carrying signals properly, and afflicted persons can experience problems with muscular coordination, vision and other sensory problems, and paralysis. The root cause of the disease is unknown; many scientists believe an as-yet-unidentified virus or virion may be the culprit, but recent research points strongly to a genetic factor as well.