A newborn screening program identifies an infant with hemoglobin Bart in 12% of red cells at birth, which disappears by 3 months. The child remains healthy. What is the most likely genotype?

• A One alpha-globin gene deletion (-alpha/alpha-alpha)
• B Four alpha-globin gene deletions (--/--)
• C Three alpha-globin gene deletions (--/-alpha)
• D Two alpha-globin gene deletions on the same chromosome (--/alpha-alpha) ✓

Explanation

Two alpha-gene deletions cause alpha-thalassemia trait with mild microcytosis; excess gamma chains form small amounts of Hb Bart detectable only in the neonatal period, disappearing as gamma switches to beta. One deletion produces a normal electrophoresis even at birth, while three deletions give persistent HbH disease and four deletions cause fatal hydrops fetalis with massive Hb Bart.

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.