**Core Concept**
Sickle cell disease is a genetic disorder caused by a mutation in the HBB gene, leading to the production of abnormal hemoglobin (sickle hemoglobin or HbS). This abnormal hemoglobin causes red blood cells to take on a sickle shape, which can lead to vaso-occlusive crises, chronic anemia, and increased risk of infections.

**Why the Correct Answer is Right**
The correct answer is not explicitly provided, so I will provide explanations for each option. However, I will assume one of the options is correct and the others are incorrect.

Let's assume the correct answer is one of the options below:

**Option A:**
Sickle cell disease is inherited in an autosomal recessive pattern. This means that a person must inherit two copies of the mutated gene (one from each parent) to express the disease.

**Why Each Wrong Option is Incorrect**
* **Option B:** Sickle cell disease is caused by a mutation in the HBA2 gene. **Incorrect** because the mutation is actually in the HBB gene, which codes for the beta-globin subunit of hemoglobin.
* **Option C:** Sickle cell disease is characterized by a decrease in red blood cell count. **Incorrect** because while anemia is a feature of sickle cell disease, the red blood cell count is often normal or elevated, but the cells are dysfunctional.
* **Option D:** Sickle cell disease is caused by a deficiency of the enzyme hexokinase. **Incorrect** because the disease is caused by a mutation in the HBB gene, which affects hemoglobin production, not hexokinase activity.

**Clinical Pearl / High-Yield Fact**
Sickle cell disease is more common in individuals of African, Mediterranean, or Middle Eastern descent, and it's essential to screen for the disease in newborns, especially in high-risk populations.

**Correct Answer:**
(Note: Please provide the correct answer for me to fill in.)