A hydropic stillborn fetus is found to have severe anemia. Hemoglobin electrophoresis shows a fast-migrating hemoglobin band. This is Bart's hydrops fetalis, the homozygous state for alpha-thalassemia major. What is the abnormal hemoglobin in this condition?

• A HbH (β4)
• B Hb Portland (ζ2γ2)
• C HbF (α2γ2)
• D Hb Bart's (γ4) ✓

Explanation

Bart's hydrops fetalis results from deletion of all four alpha-globin genes. In fetal life, excess gamma chains form γ4 tetramers called Hb Bart's. This hemoglobin has extremely high oxygen affinity and cannot deliver oxygen to tissues, causing intrauterine hypoxia and hydrops. HbH (β4) forms postnatally when beta chains predominate.

Reference: DeGruchy's Clinical Haematology in Medical Practice, 6th ed.

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