PIGA and paroxysmal nocturnal hemoglobinuria: PNH is a monogenic disease caused by acquired mutations in the phosphatidylinositol glycan anchor biosynthesis class A gene (PIGA) in hematopoietic stem cells, giving rise to red blood cells (RBCs), platelets, and white blood cells (WBCs) with the PNH phenotype.1,24,25 The disease starts with the expansion of the hematopoietic stem cell that has the PIGA mutation conferring lack of glycophosphatidylinositol (GPI) anchors.