Pure red cell aplasia (PRCA) is a rare condition that affects the bone marrow. Bone marrow contains stem cells which develop into the red blood cells that carry oxygen through the body, the white blood cells that fight infections, and the platelets that help with blood clotting. In people with PRCA, the bone marrow makes a reduced number of red blood cells (called anemia). As a result, affected people may experience fatigue, lethargy, and pale skin. PRCA has many different causes. A rare congenital form of PRCA, called Diamond Blackfan syndrome, is an inherited condition that is also associated with other physical abnormalities. PRCA can also be due to certain medications, infections, pregnancy, renal failure, and conditions such as thymomas, autoimmune disease (such as systemic lupus erythematosus), cancers of the blood, and solid tumors. In many cases, the cause of the condition is unknown (idiopathic).