**Core Concept**
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, bone marrow failure, and blood clot formation. It results from a defect in the production of complement regulatory proteins on the surface of blood cells.

**Why the Correct Answer is Right**
PNH is caused by mutations in the PIGA gene, which is responsible for the synthesis of the glycosylphosphatidylinositol (GPI) anchor. The GPI anchor is essential for the attachment of complement regulatory proteins, such as CD55 and CD59, to the surface of blood cells. Without these proteins, the complement system can activate and cause the destruction of red blood cells, leading to hemolysis and the characteristic symptoms of PNH.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because PNH is not caused by defects in the complement system itself, but rather by the lack of complement regulatory proteins on the surface of blood cells.
**Option B:** This option is incorrect because PNH is not a result of bone marrow failure, but rather a consequence of the destruction of red blood cells.
**Option C:** This option is incorrect because PNH is an acquired disease, not a congenital disorder.

**Clinical Pearl / High-Yield Fact**
A key feature of PNH is the presence of schistocytes (fragmented red blood cells) in the peripheral blood smear, which is a result of the complement-mediated destruction of red blood cells.

**Correct Answer: C. PIGA gene mutations**