Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disease where red blood cells rupture due to the immune system mistakenly attacking them. This happens because of a mutation in the bone marrow stem cells, which prevents red blood cells from getting a necessary protective marker. Patients may experience anemia, fatigue, and dark urine, especially after sleep. Treatments include drugs that suppress the immune system’s attack or, in severe cases, risky bone marrow transplants. While current treatments can improve life quality, they also carry risks, and research for better options continues.