PNH is an acquired hematopoietic stem cell disorder caused by somatic mutations in the phosphatidylinositol glycan class A (PIGA) gene, leading to a deficiency of glycosylphosphatidylinositol (GPI)-anchored proteins such as CD55 and CD59 [2]. The gene discussed is CD55; the disease is paroxysmal nocturnal hemoglobinuria.