Acquired mutation of PIGA gene that encodes a GPI anchor for decay-accelerating factor (DAF/CD55) and membrane inhibitor of reactive lysis (MIRL/CD59) in the cell membrane → ↑ complement-mediated intravascular RBC/WBC/platelet lysis.- Acquired mutation in a hematopoietic stem cell.

- ↑ incidence of acute leukemias- Associated with aplastic anemia

Findings: - Triad: Coombs ⊝ hemolytic anemia, pancytopenia, venous thrombosis- Venous thrombosis in unusual areas (eg, hepatic, cerebral, abdominal veins)- Patients may report red or pink urine (from hemoglobulinuria)- Labs: CD55/59-⊝ RBCs on flow cytometry

Treatment: Eculizumab (C5 complement inhibitor)