PIGA and paroxysmal nocturnal hemoglobinuria: Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal stem cell disease characterized by venous thrombosis and intravascular hemolysis, caused by a somatic mutation in the phosphatidylinositol N-acetylglucosaminyltransferase subunit A (PIGA) gene located on chromosome X [1–3].