0 or 1 of previous expression; also forces minimal matching when an expression might match several strings within a search string. \. Preceding one of the above, it makes it a literal instead of a special character. Preceding a special matching character, see below.
sickle cell disease. Sickle cell anemia, a common form of sickle cell disease, is caused by a particular mutation in the HBB gene. This mutation results in the production of an abnormal version of beta-globin called hemoglobin S or HbS. In this condition, hemoglobin S replaces both beta-globin subunits in hemoglobin.
1 People with sickle-cell anemia have a gene that causes the blood protein hemoglobin to form abnormally. 2  As a result, red blood cells are produced in a sickle shape. â 3 This can cause painful episodes called crises, and even strokes and heart attacks,â Murray says. Sickle-cell anemia. 2  People with sickle-cell anemia have a gene that causes the blood protein hemoglobin to form abnormally. 3  As a result, red blood cells are produced in a sickle shape.