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Glucose-6-phosphate-dehydrogenase deficiency
88%
231/264
Pyruvate kinase deficiency
1%
2/264
Paroxysmal nocturnal hemoglobinuria
4%
10/264
Hereditary spherocytosis
5%
12/264
Cold immune hemolytic anemia
2%
5/264
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Normocytic anemia, back pain and hemoglobinuria following oxidant stresses (dapsone therapy in this vignette) in a patient of Mediterranean descent are highly suggestive of Glucose-6-phosphate-dehydrogenase (G6PD) deficiency. G6PD deficiency is an X-linked recessive disorder most commonly found in Greeks, Italians, and African Americans. The deficiency of G6PD reduces the synthesis of the reduced form of NADPH, which subsequently decreases glutathione (GSH) levels. Because GSH neutralizes hydrogen peroxide, the absence of GSH in G6PD deficiency allows peroxidase to oxidize hemoglobin. Anemia is often precipitated by oxidant stresses that induce hemolysis. Infections are the most common cause, followed by drugs including dapsone, antimalarials, and sulfonamide antibiotics. Frank discusses the diagnosis and management of G6PD deficiency, concluding that diagnosis is best made using a fluorescent spot test that assesses how readily NADPH is converted to its reduced form. Hemolysis is often self-limited, and therapy should center around primary prevention via avoidance of oxidative stressors that precipitate hemolysis. Mason et al. review clinical findings in G6PD deficiency anemia. Early findings include jaundice and elevated LDH levels. Blood smears often show anisocytosis, polychromasia, and poikilocytes with abnormal forms in the early stages of acute episodes. Figure A depicts bite cells in the main panel and Heinz bodies in the panel inset. Heinz bodies consist of denatured hemoglobin that precipitates within RBCs. Bite cells appear after splenic macrophages remove Heinz bodies from RBCs. Illustration A summarizes the biochemical pathway involved in G6PD deficiency. Incorrect Answers: Answer 2: Pyruvate kinase deficiency is an autosomal recessive disease in which decreased RBC ATP levels lead to membrane damage. Peripheral blood smear shows echinocytes ('burr cells,' or red blood cells with thorny projections). Answer 3: A deficiency in decay accelerating factor (DAF) causes paroxysmal nocturnal hemoglobinuria in which RBCs are vulnerable to complement attachment and the membrane attack complex. Peripheral blood smear shows pancytopenia. Answer 4: Hereditary spherocytosis is an autosomal dominant (75%) or recessive (25%) disorder marked by a deficiency in RBC membrane proteins, leading to RBC membrane fragility. Peripheral blood smear shows spherocytes. Answer 5: Cold immune hemolytic anemia is caused by IgM-mediated RBC hemolysis. Peripheral blood smear shows RBC agglutination.
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