<qa>  What is the main feature of sickle cell disease?Sickle cell disease is a genetic red blood cell disorder that can result in blocking of the small blood vessels from sickle shaped red blood cells. This causes pain, the main feature of sickle cell disease. Also, low amounts of nitric oxide can occur in sickle cell disease, a substance important for widening the blood vessel wall and therefore preventing blockage of the small blood vessels. 