Sickle-cell disease (SCD), also known as sickle-cell anaemia (SCA), is a hereditary blood disorder, caused by an abnormality in the oxygen-carrying protein haemoglobin found in red blood cells. This leads to a propensity for the cells to assume an abnormal, rigid, sickle-like shape under certain circumstances. Sickle-cell disease is associated with a number of acute and chronic health problems, such as severe infections, attacks of severe pain ("sickle-cell crisis"), stroke, and an increased risk of death.