Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life-threatening blood disorder characterized by the destruction of red blood cells (hemolysis). It is caused by a genetic mutation that results in the absence of certain proteins on the surface of red blood cells. This leads to the destruction of red blood cells by the body's own immune system. Symptoms of PNH include anemia, fatigue, abdominal pain, and blood clots. Treatment typically involves medications to reduce the destruction of red blood cells and to prevent blood clots.