PNH is an acquired defect and is clonal. Eventually the clone dominates the RBC population. Spring from GPI linked proteins/anchor. It attaches many proteins to the surface. PIG-A gene mutations involved. Episodic hemolysis at night- n/n anemia, might evolve to AA or AML. CELLS HAVE diminished DAF (CD55) and diminished MIRL (CD59), decreased CD16 and CD48. Sucrose hemolysis test, enhanced hemolysis. And Ham test is positive. FLOW cytometry.