A disorder that causes abnormal red blood cells, and these cells can clog blood vessels. Sickle cell disease is the most common of the inherited blood disorders, and is seen primarily in black Americans and black Africans. A sickle cell crisis causes pain because blood vessels become blocked and the defective red blood cells can damage organs in the body. The most commonly affected organs include: lungs, liver, bone, muscles, brain, spleen, penis, eyes, and kidneys. Patients also experience chronic anemia.