Paroxysmal nocturnal haemoglobinuria (PNH) results from a somatic mutation in PIGA gene causing absence of which cell surface anchor proteins that protect RBCs from complement?

• A CD35 (CR1, complement receptor 1) and CD46 (MCP)
• B CD55 (DAF — decay-accelerating factor) and CD59 (MIRL — protectin) ✓
• C Complement factor H and factor I
• D Clusterin (SP-40/40) and vitronectin

Explanation

PIGA mutation causes deficiency of GPI (glycosylphosphatidylinositol) anchor synthesis, leading to absence of all GPI-anchored proteins including CD55 (DAF — inhibits C3/C5 convertase assembly) and CD59 (MIRL/protectin — inhibits C5b-9 MAC formation). Without these complement regulators, RBCs are vulnerable to terminal complement-mediated intravascular haemolysis. Treatment with eculizumab (anti-C5 monoclonal antibody) prevents MAC formation. CD35 and CD46 are complement regulatory proteins but are NOT GPI-anchored, and are preserved in PNH.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.