In PNH, a mutation in the endogenous X‐linked PIG‐A gene in hematopoietic bone marrow stem cells causes a disruption in the synthesis of glycosyl phosphatidyl inositol (GPI), which makes erythrocytes originating from the mutant bone marrow stem cells deficient in CD55 and CD59 GPI‐anchored surface proteins vulnerable for complement‐mediated lysis.31 The gene discussed is CD55; the disease is paroxysmal nocturnal hemoglobinuria.