Deletion of two alpha-globin genes primarily results in which condition?

• A. Thalassemia trait
• B. HbH disease
• C. Hydrops fetalis
• D. Sideroblastic anemia

Answer: (A)

The key idea is that how many alpha-globin genes are deleted determines the severity of alpha-thalassemia. With two of the four alpha-globin genes deleted, enough alpha chains remain to form adult hemoglobin, but production is reduced, producing alpha-thalassemia trait (mild microcytic, hypochromic anemia). Many individuals are carriers and have little to no symptoms, though red cell indices show small, pale cells. If three genes were deleted, HbH disease would result due to excess beta chains forming HbH, a more serious hemolytic condition. Deleting all four genes causes hydrops fetalis, typically fatal before or shortly after birth. So two-gene deletion most directly corresponds to thalassemia trait.