A Study of Etavopivat in Patients With Thalassemia or Sickle Cell Disease

Inclusion Criteria: * Provision of consent * Female patients of childbearing potential must use acceptable methods of contraception, male patients are willing to use barrier methods of contraception Cohort A (Sickle Cell Disease Transfusion Cohort) * Confirmed diagnosis of sickle cell disease * Chronically red blood cell transfused (sample or exchange \[manual or via electrophoresis\]) for primary stroke prevention or due to previous stroke. Chronic red blood cell transfusion is defined as: ≥ 6 red blood cell units in the previous 24 weeks before the first dose of study treatment and no transfusion-free period for \> 35 days during that period * At least 24 months of chronic monthly red blood cell transfusions for secondary stroke prevention/treatment of primary stroke (initial completed overt clinical stroke with documented infarction on brain computed tomography \[CT\] or magnetic resonance imaging \[MRI\]) * Prior to screening OR at least 12 months of chronic RBC transfusions for primary stroke prevention (abnormal TCD) prior to screening * Documented adequate monthly transfusions with average HbS ≤ 45% (the upper limit of the established academic community standard) for the previous 12 weeks of red blood cell transfusions before the first dose of study treatment Cohort B (Thalassemia Transfusion Cohort) * Documented diagnosis of β-thalassemia, Hemoglobin E/ β-thalassemia or Hemoglobin H (α-thalassemia), or other thalassemia variant * Chronically transfused, defined as: ≥ 6 red blood cell units in the previous 24 weeks before the first dose of study treatment and no transfusion-free period for \> 35 days during that period Cohort C (Thalassemia Non-transfused Cohort) * Documented diagnosis of β-thalassemia, Hemoglobin E/ β-thalassemia or Hemoglobin H (α-thalassemia), or other thalassemia variant * Hemoglobin ≤ 10 g/dL Exclusion Criteria: * Female who is breast feeding or pregnant * Hepatic dysfunction characterized by: * Alanine aminotransferase (ALT) \> 4.0 × upper limit of normal (ULN) * Direct bilirubin \> 3.0 × ULN * History of cirrhosis * Known human immunodeficiency virus (HIV) positivity * Active hepatitis B or hepatitis C infection * Severe renal dysfunction or on chronic dialysis * History of malignancy within the past 2 years prior to treatment Day 1 requiring systemic chemotherapy and/or radiation. * Patients with malignancy considered surgically cured are eligible (eg, non- melanoma skin cancer, cancer of the cervix in-situ, ductal carcinoma in situ \[Stage 1\], Grade 1 endometrial cancer) * History of unstable or deteriorating cardiac or pulmonary disease within 6 months prior to consent including but not limited to the following: * Unstable angina pectoris or myocardial infarction or elective coronary intervention * Congestive heart failure requiring hospitalization * Uncontrolled clinically significant arrhythmias * Symptomatic pulmonary hypertension