A 24-year-old pregnant woman of Southeast Asian origin presents at 28 weeks with hydrops fetalis on ultrasound. Hemoglobin analysis of cord blood shows predominantly Hb Bart's (gamma-4 tetramers). What is the underlying genetic defect?
- A Deletion of all four alpha-globin genes ✓
- B Deletion of two alpha-globin genes on the same chromosome (cis deletion)
- C Homozygous beta-globin gene mutation
- D Deletion of one alpha-globin gene
Correct answer: A. Deletion of all four alpha-globin genes
Explanation
Hb Bart's hydrops fetalis syndrome results from deletion of all four alpha-globin genes (--/-- genotype), producing only gamma-4 tetramers (Hb Bart's) which cannot deliver oxygen to tissues. This is most common in Southeast Asian populations where the cis deletion (--SEA) carrier state is prevalent. It is incompatible with extrauterine life without intrauterine transfusions.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.