**Core Concept**
Sickle cell anemia 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 become misshapen and break down prematurely. The treatment aims to reduce the frequency of painful crises, slow disease progression, and improve quality of life.

**Why the Correct Answer is Right**
Hydroxyurea (also known as hydroxycarbamide) is used to treat sickle cell anemia by increasing fetal hemoglobin (HbF) production, which helps to reduce the formation of sickle-shaped red blood cells. HbF competes with HbS for binding sites on the hemoglobin tetramer, thereby reducing the polymerization of HbS and the formation of sickle-shaped cells. This leads to a decrease in the frequency of painful crises and a reduction in the severity of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because hydrochlorothiazide is a diuretic used to treat hypertension and edema, not sickle cell anemia.
**Option B:** This option is incorrect because folic acid is a vitamin supplement used to prevent megaloblastic anemia, particularly in patients on long-term anticonvulsant therapy, but it does not directly treat sickle cell anemia.
**Option C:** This option is incorrect because acetazolamide is a carbonic anhydrase inhibitor used to treat glaucoma, epilepsy, and altitude sickness, but it is not used to treat sickle cell anemia.

**Clinical Pearl / High-Yield Fact**
Hydroxyurea is the first FDA-approved medication for the treatment of sickle cell anemia and has been shown to reduce the frequency of painful crises and the need for blood transfusions.

**Correct Answer:** C. Hydroxyurea