An inherited disease characterized by periods of relative health alternating with episodes of severe illness caused when sickle-shaped red blood cells block small blood vessels.

Sickle-cell anemia is a genetic disorder that causes the victim's red blood cells to become stiff and sickleshaped. The disease causes a variety of symptoms, the most prominent of which are crises, caused when the misshapen cells block small capillaries, preventing the flow of oxygen to limbs and organs. This blockage is called sludging. The crises range from mild bone aches to debilitating body pain and can last up to a week. In the most severe cases, stroke can occur. Currently, there is no cure for the disease.

A child with sickle-cell anemia has inherited one copy of the defective gene from each parent. Two sickle-cell carriers have a 25% chance of having a child with sickle-cell and a 50% chance of having...