Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disease defined by bone marrow failure that results in the formation of abnormal blood cells. PNH occurs when there is an acquired (not inherited or born with) genetic mutation in the PIG-A gene, the gene that is responsible for producing normal blood cells for the body. When this gene becomes mutated, it creates a PNH clone of bone marrow cells that produce defective blood cells. These defective blood cells lack proteins that naturally occur on the surface of these cells, which normally function to protect these blood cells from being destroyed by a substance in the blood called complement. The absence of these proteins in people living with PNH leave the PNH clone blood cells vulnerable to attack from the complement system, which is part of the body’s normal immune system that is designed to fight infections.
In PNH, the attack of the complement system on these abnormal blood cells causes the blood cells to break apart, a process referred to as hemolysis. Hemolysis occurs in everyone and is how old blood cells are replaced by new ones. In people living with PNH however, hemolysis occurs much faster than normal and can cause an increased, rapid destruction of red blood cells. When red blood cells break apart, the hemoglobin inside of them is released into the body. Hemoglobin is the part of your red blood cells that carries oxygen around the body. The release of hemoglobin from the red blood cells into the body causes many of the PNH symptoms.