A newborn has severe hemolytic anemia requiring exchange transfusion. Hemoglobin electrophoresis shows predominantly Hb Barts (γ4). This pattern is diagnostic of:
- A Beta-thalassemia major
- B Sickle cell disease with high fetal hemoglobin
- C Alpha-thalassemia with deletion of all four alpha-globin genes (Hb Barts hydrops fetalis) ✓
- D Hemoglobin H disease (three alpha-gene deletion)
Correct answer: C. Alpha-thalassemia with deletion of all four alpha-globin genes (Hb Barts hydrops fetalis)
Explanation
Hb Barts (γ4) forms when no functional alpha-globin chains are produced (--/--, deletion of all four alpha genes). Gamma chains form homotetramers (Hb Barts) with very high oxygen affinity and no Bohr effect, making them physiologically useless. This causes severe tissue hypoxia, hydrops fetalis, and is usually incompatible with extrauterine life. Hemoglobin H (β4) forms in three-gene deletion; Hb F predominates in beta-thalassemia major.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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