Which one of the following statements about Hemoglobin S (HbS) is not true –
**Question:** Which one of the following statements about Hemoglobin S (HbS) is not true -
A. Hemoglobin S is a genetic disorder resulting from a single gene mutation
B. Hemoglobin S is the cause of sickle cell anemia
C. Hemoglobin S has a similar structure to normal hemoglobin (HbA)
D. Hemoglobin S does not affect the oxygen-carrying capacity of red blood cells
**Correct Answer:** D. Hemoglobin S does not affect the oxygen-carrying capacity of red blood cells
**Core Concept:** Hemoglobin S (HbS) is a hemoglobin variant that occurs due to a single gene mutation, specifically a valine to glutamic acid substitution at position 6 in the beta-globin chain. This mutation leads to a change in the protein structure of hemoglobin, causing it to precipitate when deoxygenated and forming polymer fibers within red blood cells (RBCs).
**Why the Correct Answer is Right:** The correct answer is not true because hemoglobin S does significantly affect the oxygen-carrying capacity of red blood cells. When HbS deoxygenates, it polymerizes, causing the RBCs to become rigid and crescent-shaped, known as sickle cells. These deformed RBCs are unable to flow easily through small blood vessels, leading to reduced blood flow and oxygen delivery to tissues, which causes the clinical manifestations of sickle cell anemia.
**Why Each Wrong Option is Incorrect:**
A. This statement is true, as HbS is indeed a genetic disorder resulting from a single gene mutation.
B. This statement is false, as HbS does contribute to the development of sickle cell anemia due to the shape change and reduced blood flow mentioned above.
C. This statement is incorrect because the altered structure of HbS does affect its binding affinity for oxygen compared to normal hemoglobin (HbA).
D. This statement is false because HbS does significantly affect the oxygen-carrying capacity of RBCs, as explained above.
**Clinical Pearl:** Understanding the pathophysiology of hemoglobin S is crucial for diagnosing and managing patients with sickle cell anemia. The clinical manifestations and complications related to HbS and sickle cell anemia are essential to comprehend for competent clinical practice and patient care.