CD59 defect is seen as marker of which disease
**Core Concept**
CD59, also known as protectin, is a surface protein that inhibits the formation of the membrane attack complex (MAC) by preventing the insertion of C9 into the complement cascade. This prevents cell lysis and is an essential mechanism for protecting cells from complement-mediated damage.
**Why the Correct Answer is Right**
The correct answer is related to the Paroxysmal Nocturnal Hemoglobinuria (PNH). In PNH, a defect in the PIGA gene leads to a deficiency of glycosylphosphatidylinositol (GPI) anchors, resulting in the loss of surface proteins, including CD59. This loss of CD59 makes red blood cells more susceptible to complement-mediated lysis, resulting in the characteristic hemolytic anemia seen in PNH.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CD59 defect is not a marker of autoimmune hemolytic anemia, which is caused by antibodies against red blood cell antigens.
**Option B:** This option is incorrect because CD59 defect is not a marker of glucose-6-phosphate dehydrogenase (G6PD) deficiency, which is a genetic disorder affecting the enzyme G6PD.
**Option C:** This option is incorrect because CD59 defect is not a marker of hereditary spherocytosis, which is a genetic disorder affecting the red blood cell membrane.
**Clinical Pearl / High-Yield Fact**
PNH is a rare and life-threatening disease characterized by the destruction of red blood cells, bone marrow failure, and the presence of blood clots. A CD59 defect is a key diagnostic marker for PNH, and prompt recognition and treatment are essential to prevent complications.
**Correct Answer:** C. PNH.