**Core Concept**
Sickle cell disease (SCD) is a genetic disorder caused by a mutation in the HBB gene, leading to the production of abnormal hemoglobin (HbS) that causes red blood cells to take on a sickle shape under low oxygen conditions. This abnormal hemoglobin polymerizes and causes red blood cells to become rigid, leading to vaso-occlusion, tissue ischemia, and chronic anemia.

**Why the Correct Answer is Right**
Sickle cell disease is an autosomal recessive disorder, meaning that a person must inherit two copies of the mutated gene (one from each parent) to express the disease. The disease is characterized by the polymerization of deoxyhemoglobin S (HbS), which is facilitated by low oxygen tension, dehydration, and increased temperature. This polymerization causes the red blood cells to become rigid and sickle-shaped, leading to vaso-occlusion and tissue ischemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true. Sickle cell disease is indeed caused by a mutation in the HBB gene.
**Option B:** This statement is true. The polymerization of deoxyhemoglobin S (HbS) is facilitated by low oxygen tension, dehydration, and increased temperature.
**Option C:** This statement is false. Sickle cell disease is an autosomal recessive disorder, meaning that a person must inherit two copies of the mutated gene (one from each parent) to express the disease. It is not an X-linked disorder.

**Clinical Pearl / High-Yield Fact**
It is essential to note that sickle cell disease is a genetic disorder, and therefore, there is no cure. However, various treatments are available to manage the symptoms and prevent complications, such as hydroxyurea, which can reduce the frequency of painful crises and the need for blood transfusions.

**Correct Answer: C. Sickle cell disease is an autosomal recessive disorder.