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A defect in the complement mediated pathway
1%
1/76
A mutation from glutamic acid to valine
11%
8/76
A mutation from glutamic acid to lysine
42%
32/76
A mutation in red blood cell cytoskeletal proteins
9%
7/76
An inability to produce reducing equivalents
36%
27/76
Select Answer to see Preferred Response
This patient with conjunctival pallor, fatigue, and a normal mean corpuscular volume with crystals seen within red blood cells on a smear most likely has hemoglobin C disease, which is associated with a glutamic acid to lysine mutation in hemoglobin. Hemoglobin C disease is caused by a mutation from glutamic acid to lysine in hemoglobin leading to a normocytic, hemolytic anemia. The appearance of crystals along with target cells on peripheral blood smear is characteristic of this disorder. Another method of diagnosing hemoglobin C disease is hemoglobin electrophoresis or high-performance liquid chromatography, where patients will have mostly hemoglobin C and absent levels of hemoglobin A. Finally, since hemoglobin C disease leads to extravascular hemolysis, it results in indirect hyperbilirubinemia with increased lactate dehydrogenase levels. Figure A shows target cells and red blood cells with internal crystals consistent with hemoglobin C disease. Incorrect Answers: Answer 1: A defect in the complement-mediated pathway can caused paroxysmal nocturnal hemoglobinuria, which presents with intravascular hemolysis related to complement mediated destruction of red blood cells. Crystals are not seen on histology for this disorder. Answer 2: A mutation in hemoglobin from glutamic acid to valine leads to sickle cell trait or disease, which presents with anemia and pain crises after destruction of red blood cells. It would not present with crystals on peripheral blood smear. Answer 4: A mutation in red blood cell cytoskeletal proteins is associated with hereditary spherocytosis, which would present with hemolytic anemia due to abnormally round cells rather than cells with crystals on peripheral blood smear. Answer 5: An inability to produce reducing equivalents is associated with glucose-6-phosphate dehydrogenase deficiency, which can lead to hemolytic anemia after a trigger like fava beans. It would not present with crystals in the peripheral blood smear. Bullet Summary: Hemoglobin C causes a mild extravascular hemolytic anemia and is associated with a mutation from glutamic acid to lysine on the hemoglobin protein.
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