Silent carriers of alpha-thalassemia are missing how many alpha genes?

• A. 1
• B. 2
• C. 3
• D. 4

Answer: (A)

In alpha-thalassemia, there are four alpha-globin genes in total—two on each chromosome 16. The severity of the condition depends on how many of these genes are deleted. A silent carrier has a deletion of just one alpha-globin gene, leaving three functional alpha genes. That gene dosage is enough to maintain normal hemoglobin production and RBC appearance, so there are no symptoms, and the person is clinically silent. Deleting two genes can cause a mild trait with some microcytosis, deleting three leads to HbH disease with more significant anemia, and deleting all four results in hydrops fetalis.