Background. Sickle cell anaemia (SCA) is the most prevalentmonogenic disease in Brazil. In SCA, haemoglobin S (HbS) is formed, whichmodifies red blood cell morphology. Intravascular haemolysis occurs, in which free Hb and free radicals degrade nitric oxide (NO) and release arginase, which reduces arginine levels. Because arginine is a substrate for NO formation, this decrease leads to reduced NO (vasodilator) s...