1. PNH is a rare acquired clonal blood disorder caused by a mutation in the *PIGA gene*.
2. This mutation leads to loss of *GPI-anchored protective proteins* (CD55 & CD59) on RBC membranes.
3. Without these proteins, RBCs are vulnerable to *complement-mediated intravascular hemolysis*.
4. Some *extravascular hemolysis* also occurs via splenic macrophages.
5. Clinical features include *fatigue, dark urine (especially in the morning), abdominal pain, and thrombosis*.
6. *Venous thrombosis* in unusual sites (e.g., portal, cerebral veins) is a major cause of death.
7. Diagnosis is made by *flow cytometry* showing deficiency of CD55/CD59 on blood cells.
8. First-line treatment is *Eculizumab* or *Ravulizumab*, which block complement activation.
9. Patients require regular follow-up for *hemolysis, cytopenias, thrombosis, and kidney function*