Question:medium
CD59 is a marker of which disease?
CD59 is a marker of which disease?
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CD59 is a GPI-anchored complement regulator lost when the GPI anchor fails.
Updated On: Jun 24, 2026
- PNH
- PTEN
- BRR
- Cowden syndrome
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The Correct Option is A
Solution and Explanation
Step 1: Trace the defect. PNH begins with an acquired $PIGA$ mutation that blocks synthesis of the GPI anchor, the tether that holds certain proteins on the cell surface.
Step 2: Among the proteins lost are the complement brakes CD55 and CD59. With CD59 missing, red cells cannot resist complement and undergo intravascular hemolysis, so CD59 deficiency is the marker pointing to PNH.
Step 3: This is why the diagnostic test is flow cytometry demonstrating absent CD55 and CD59 on blood cells, reflecting their heightened susceptibility to complement.
Step 4: The remaining options cluster as PTEN hamartoma tumor syndromes, namely Cowden and Bannayan-Riley-Ruvalcaba syndromes, which are unrelated to CD59. Thus the answer is PNH.
\[\boxed{\text{Paroxysmal nocturnal hemoglobinuria (PNH)}}\]
Step 2: Among the proteins lost are the complement brakes CD55 and CD59. With CD59 missing, red cells cannot resist complement and undergo intravascular hemolysis, so CD59 deficiency is the marker pointing to PNH.
Step 3: This is why the diagnostic test is flow cytometry demonstrating absent CD55 and CD59 on blood cells, reflecting their heightened susceptibility to complement.
Step 4: The remaining options cluster as PTEN hamartoma tumor syndromes, namely Cowden and Bannayan-Riley-Ruvalcaba syndromes, which are unrelated to CD59. Thus the answer is PNH.
\[\boxed{\text{Paroxysmal nocturnal hemoglobinuria (PNH)}}\]
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