Which is not a feature of paroxysmal nocturnal hemoglobinuria-
**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 the potential for blood clot formation. It results from mutations in the PIGA gene, leading to a deficiency of glycosylphosphatidylinositol (GPI)-anchored proteins on the surface of blood cells.
**Why the Correct Answer is Right**
PNH is characterized by the complement-mediated destruction of red blood cells, which leads to hemolytic anemia and the release of free hemoglobin into the urine. This is due to the deficiency of CD55 and CD59, which are GPI-anchored proteins that protect red blood cells from the complement system. The other features of PNH include bone marrow failure, thrombosis, and the presence of PNH clones in the bone marrow, blood, or both.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a feature of PNH. While PNH can be associated with other hematologic abnormalities, such as anemia and thrombocytopenia, the specific mention of "increased platelet count" is not a characteristic of the disease.
**Option B:** This option is a feature of PNH. The disease is indeed associated with the destruction of red blood cells, which leads to hemolytic anemia and the release of free hemoglobin into the urine.
**Option C:** This option is a feature of PNH. Bone marrow failure is a hallmark of the disease, which can lead to pancytopenia and an increased risk of infections.
**Option D:** This option is a feature of PNH. Thrombosis is a significant complication of the disease, which is thought to be related to the activation of the coagulation pathway and the presence of PNH clones in the blood.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that PNH is often associated with a history of unexplained hemolytic anemia, bone marrow failure, and thrombosis. A high index of suspicion is necessary for diagnosis, and bone marrow biopsy may be required to confirm the presence of PNH clones.
**Correct Answer:** A.