Sickle cell anaemia is a non-infectious chronic disease. If not treated, sickle cell anaemia can be painful and life-threatening. Sickle cell anaemia is caused by a base substitution mutation in the gene coding for the ẞ-globin polypeptide of haemoglobin. This leads to a change in the primary structure of the polypeptide, as valine is present instead of glutamine. This results in abnormal sickle-shaped red blood cells, which stick together in blood vessels. Symptoms of sickle cell anaemia include painful attacks when red blood cells block capillaries in tissues and organs.