A 25-year-old West African man has mild hemolytic anemia with splenomegaly. Peripheral smear shows numerous target cells and hexagonal red cell crystals within erythrocytes. Hemoglobin electrophoresis shows a beta globin variant accounting for nearly all adult hemoglobin. The underlying mutation substitutes which amino acid?

• A Valine for glutamic acid at position 6
• B Lysine for glutamine at position 26
• C Glutamic acid for valine at position 6
• D Lysine for glutamic acid at position 6 ✓

Explanation

Hemoglobin C disease results from a point mutation substituting lysine for glutamic acid at the sixth position of the beta globin chain, the same codon affected in sickle hemoglobin but with a different amino acid. Reduced solubility of HbC causes crystal formation and target cells with mild extravascular hemolysis. Valine for glutamate at position 6 defines HbS, glutamic acid for valine is the reverse and nonexistent, and lysine for glutamine at position 26 describes hemoglobin E, common in Southeast Asia.

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.