In hemolytic disorders, such as sickle cell disease, thalassemia, or paroxysmal nocturnal hemoglobinuria, NO deficiency is caused by release of arginase-1 from erythrocytes, leading to consumption of L-arginine finally resulting in vasoconstriction and pulmonary hypertension [13, 16, 22, 23]. The gene discussed is ARG1; the disease is paroxysmal nocturnal hemoglobinuria.