(CIT): NIH Consensus Development Conference Sickle cell disease is an inherited blood disorder that affects between 50,000 and 75,000 people in the United States, and is most common among people whose ancestors come from sub-Saharan Africa, South and Central America, the Middle East, India, and the Mediterranean basin. Sickle cell disease occurs when an infant inherits the gene for sickle hemoglobin from both parents (Hb SS, or sickle cell anemia), or the gene for sickle hemoglobin from one parent and another abnormal hemoglobin gene from the other parent. Each year, approximately 2,000 babies with sickle cell disease are born in the United States. The condition is chronic and lifelong, and is associated with a decreased lifespan. In addition, approximately 2 million Americans carry the sickle cell trait, which increases the public health burden as this disorder is passed on to future generations. The red blood cells in people with sickle cell disease become deoxygenated (or depleted of oxygen), and crescent-shaped or "sickled." The cells become sticky, and adhere to blood vessel walls, thereby blocking blood flow within limbs and organs. These changes lead to acute painful episodes, chronic pain, and chronic damage to the brain, heart, lungs, kidneys, liver, and spleen. Infections and lung disease are leading causes of death. Pain crises are responsible for most emergency room visits and hospitalizations of people with sickle cell disease. Standard treatments for acute pain crises include painkilling medications, fluid replacement, and oxygen. In the mid-1990s, researchers began investigating the potential of hydroxyurea to reduce the number and severity of pain crises in sickle cell patients. Hydroxyurea is in a class of anti-cancer drugs and it acts to increase the overall percentage of normally structured red blood cells in the circulation. By diluting the number of cells that "sickle," it may, if taken on a daily basis, reduce their damaging effects. Hydroxyurea was approved by the FDA for use in adults with sickle cell anemia in 1998. However, there are a number of unresolved issues about the use of hydroxyurea, including a lack of knowledgeable providers who treat sickle cell disease, and patient and practitioner questions about safety and effectiveness, including concerns regarding potential long-term carcinogenesis.