A 16-year-old boy from Thailand has moderate chronic hemolytic anemia with splenomegaly. Hb is 8.2 g/dL, MCV 58 fL. Hemoglobin analysis shows HbA 70%, HbH 25%, HbA2 1.5%, with trace Hb Bart's. Smear shows microcytosis, target cells, and inclusion bodies on supravital staining. This pattern results from:
- A Deletion of three of the four alpha globin genes ✓
- B Deletion of all four alpha globin genes
- C Deletion of one of the four alpha globin genes
- D Homozygous beta-zero thalassemia mutation
Correct answer: A. Deletion of three of the four alpha globin genes
Explanation
Loss of three alpha genes leaves a single functional alpha gene, producing excess beta chains that tetramerize into HbH (beta-4), detectable as 5 to 30 percent of hemoglobin with Heinz-like inclusions on brilliant cresyl blue staining. Deletion of all four genes causes Hb Bart's hydrops fetalis, lethal in utero, while single gene deletion is silent carrier state with normal electrophoresis. Homozygous beta-zero thalassemia shows absent HbA and elevated HbF, not HbH.
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.