A Study to Investigate the Effect of Mitapivat on Transfusion Burden in Subjects With Sickle Cell Disease (SCD)

Inclusion Criteria: * Age ≥12 years. * Documented diagnosis of SCD (hemoglobin SS (HbSS), combined heterozygosity for hemoglobins S and C (HbSC), sickle cell hemoglobin (HbS)/β0-thalassemia, HbS/β+-thalassemia, or other sickle cell syndrome variants). * No more than 10 SCPCs in the 12 months before providing informed assent/consent. * At least 1 transfusion of packed RBCs in the 12 months before informed assent/consent. * Hb ≥5.5 and ≤10.5 g/dL. Hb concentration must be based on an average of at least 2 Hb concentration measurements (separated by ≥7 days) collected during the Screening Period. * Additional signs or symptoms of hemolysis, as evidenced by any laboratory assessment during the Screening Period with * Hb \<8 g/dL, or * Absolute reticulocyte count \> upper limit of normal (ULN), or * Indirect bilirubin \>ULN, or * LDH \>ULN * If taking hydroxyurea, the hydroxyurea dose must be stable for at least 90 days prior to randomization. Discontinuation of hydroxyurea requires a 90-day washout prior to informed assent/consent. * Women of childbearing potential (WOCBP) and pediatric female subjects who have attained menarche must be abstinent of sexual activities that may induce pregnancy as part of their usual lifestyle or agree to use a highly effective method of contraception from the time of providing informed assent/consent, throughout the study, and for 28 days after the last dose of study drug; if the highly effective method of contraception is hormonal contr…