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.
Sickle cell anemia is a genetic disease that causes the red blood cells to develop as a crescent shape. This can lead to blood clots when the red blood cells clump together. The disease also causes anemia, fatigue, and shortness of breath.ay Sachs Disease. Tay Sachs is a recessive genetic disease caused by a mutation in the hexosaminidase A gene, HEXA. A mutation in the gene causes fat molecules to accumulate in the brain.