HbS beta-zero thalassemia means no normal haemoglobin is produced.

• A. HbS beta-zero thalassemia means no normal haemoglobin is produced
• B. HbS beta-zero thalassemia means very high HbA production
• C. HbS beta-zero thalassemia is the same as HbS beta-plus
• D. HbS beta-zero thalassemia involves HbD

Answer: (A)

In HbS beta-zero thalassemia the beta-globin gene from one chromosome carries the sickle mutation (producing HbS), while the other beta-globin gene has a β0 mutation, meaning it does not produce any beta-globin chains at all. Since HbA (the normal adult hemoglobin) requires normal beta chains, it cannot form when one beta-globin gene is β0. The red cells can contain HbS from the HbS allele and small amounts of HbF or HbA2, but HbA, the normal adult hemoglobin, is absent. That’s why the statement describing no normal haemoglobin being produced is the best description.

The other options don’t fit because a β0 background does not produce high HbA; some HbA would require functional beta-globin production, which β0 precludes. It’s also not the same as HbS beta-plus, where some beta-globin is made and HbA can be formed. And HbD isn’t involved in this genotype, which centers on the HbS mutation paired with a β0 allele.