**Core Concept**
Sickle cell anemia is a genetic disorder characterized by the production of abnormal hemoglobin, leading to distorted red blood cells that can cause vaso-occlusion and tissue damage. The disease is caused by a mutation in the HBB gene, resulting in the production of hemoglobin S (HbS), which is more prone to polymerization under low oxygen conditions.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of sickle cell anemia. The disease is caused by the polymerization of hemoglobin S (HbS) under low oxygen conditions, leading to the formation of sickle-shaped red blood cells. This process is facilitated by the deoxygenated state of the hemoglobin, which causes the T-state of hemoglobin to bind to the HbS polymer. The polymerization of HbS leads to the distortion of the red blood cell membrane, resulting in the characteristic sickled shape.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a true statement about sickle cell anemia. The disease is indeed characterized by the production of abnormal hemoglobin, which leads to the formation of sickle-shaped red blood cells.

**Option B:** This option is incorrect because it is a true statement about sickle cell anemia. The disease is indeed caused by a mutation in the HBB gene, which results in the production of hemoglobin S (HbS).

**Option C:** This option is incorrect because it is a true statement about sickle cell anemia. The disease is indeed characterized by vaso-occlusion, which occurs when sickled red blood cells obstruct the blood vessels and cause tissue damage.

**Clinical Pearl / High-Yield Fact**
One important clinical correlation to remember is that sickle cell anemia is more common in individuals of African descent, and it is often associated with other genetic disorders, such as alpha-thalassemia.

**Correct Answer: A. This option is the only one that is not true about sickle cell anemia.**