HbS beta-zero thalassemia is defined as

HbS beta-zero thalassemia is defined as

• A. HbS beta-thalassemia with normal haemoglobin
• B. HbS beta-thalassemia with elevated normal haemoglobin
• C. HbS beta-thalassemia with some normal haemoglobin
• D. HbS beta-zero thalassemia

Answer: (D)

This definition hinges on how mutations in the beta-globin genes affect what hemoglobin is produced. HbS beta-zero thalassemia occurs when one chromosome carries the sickle mutation (HbS) and the other chromosome has beta-zero thalassemia, meaning that no beta-globin chains can be produced from that gene. Without beta-globin production from that chromosome, normal hemoglobin (HbA) cannot be formed. The result is blood that contains HbS and often elevated HbF, but no HbA. This pattern is what identifies HbS beta-zero thalassemia as a form of sickle cell disease with absent HbA. In lab tests, HbA is absent while HbS is present; HbF may be increased. If the beta-thalassemia were beta-plus, some HbA would be produced, making the pattern different.

This definition hinges on how mutations in the beta-globin genes affect what hemoglobin is produced. HbS beta-zero thalassemia occurs when one chromosome carries the sickle mutation (HbS) and the other chromosome has beta-zero thalassemia, meaning that no beta-globin chains can be produced from that gene. Without beta-globin production from that chromosome, normal hemoglobin (HbA) cannot be formed. The result is blood that contains HbS and often elevated HbF, but no HbA. This pattern is what identifies HbS beta-zero thalassemia as a form of sickle cell disease with absent HbA. In lab tests, HbA is absent while HbS is present; HbF may be increased. If the beta-thalassemia were beta-plus, some HbA would be produced, making the pattern different.