This study focuses on children with Sickle Cell Anemia (SCA), a blood disorder causing pain and other health issues. The study tests a medicine called hydroxyurea. Hydroxyurea helps reduce SCA pain and is used worldwide. Here, we're checking if a higher dose, called the Maximum Tolerated Dose (MTD), is better and safe for children in Uganda. The study will look at long-term effects on their organs and if some children respond better because of their genes.

• Children will visit the clinic every three months for up to 5 years.
• They will undergo tests like blood and urine samples, heart and lung checks, and brain scans.
• This study is done by experts at Cincinnati Children's Hospital and Mulago Hospital in Uganda.

Participants are 11-16 years old, taking hydroxyurea. Another group of untreated children will be compared to see differences in health outcomes. The study aims to find the best dose for children with SCA, while checking for side effects and benefits like improved growth and organ health.