## **Core Concept**
Sickle cell anemia is a genetic disorder that affects hemoglobin production, leading to abnormal red blood cells. It is caused by a mutation in the HBB gene that codes for the beta-globin subunit of hemoglobin. This results in the production of sickle hemoglobin (HbS).

## **Why the Correct Answer is Right**
The correct answer, , corresponds to a point mutation in the HBB gene, specifically a glutamic acid to valine substitution at position 6 of the beta-globin chain (Glu6Val). This mutation leads to the production of abnormal hemoglobin (HbS), which under low oxygen conditions, causes red blood cells to assume a sickle shape. This sickling process results in the clinical manifestations of sickle cell anemia, including vaso-occlusive crises and hemolytic anemia.

## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option does not accurately describe the genetic basis of sickle cell anemia.
* **Option B:** - While gene therapy is being explored as a treatment for sickle cell anemia, it is not the cause of the disease.
* **Option C:** - This option is not relevant to the cause of sickle cell anemia.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that sickle cell anemia is more prevalent in areas where malaria has been or is still prevalent. This is because the sickle cell trait (HbAS) offers some protection against malaria, which has led to the natural selection of the sickle cell allele in these populations.

## **Correct Answer:** . Glu6Val point mutation in the HBB gene.