Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder characterized by the destruction of red blood cells, leading to the release of hemoglobin into the urine. This condition occurs due to a mutation in the PIGA gene, which affects the surface of blood cells, making them more susceptible to destruction by the immune system. Symptoms may include dark-colored urine, fatigue, and abdominal pain. The disorder can lead to serious complications, such as blood clots and bone marrow failure. Diagnosis typically involves blood tests and flow cytometry to detect the absence of certain proteins on blood cells. Treatment options may include medications, blood transfusions, or bone marrow transplantation.