The study will test a new medicine, etavopivat, for sickle cell disease and see if it is safe and help-ful for participants with sickle cell disease who are at an increased risk of stroke. Participants will be divided into two cohorts depending on their transcranial doppler (TCD) ultrasound results and whether or not they receive hydroxyurea (medication that they may already be taking). In one cohort, participants with conditional transcranial doppler (TCD) or participants with abnormal TCD who are not able to receive hydroxyurea will be included. The study doctor will determine if the TCD result is conditional or abnormal. In another cohort, participants with conditional TCD or participants with abnormal TCD who are receiving a stable dose of hydroxyurea will be included. The study doctor will determine if the TCD result is conditional or abnormal. The participant will start a 52-week (1 year) treatment period. The participant will take 400 milligrams (mg) of etavopivat once a day for the 52 weeks. The dose of 400 mg will be taken as 2 tablets by mouth, each containing 200 mg of etavopivat. Etavopivat may be taken with or without food. Each dose should be taken with a glass of water. As part of the study, the participants will be asked to visit the clinic frequently. The participant will have the opportunity to participate in a 48-week optional extension treatment period. The optional extension treatment period will allow continued as-sessment of safety of etavopivat in paediatric patients. At the end of the study, if deemed appro-priate the participant, the caregiver, and the study doctor, the participant may be offered the op-portunity to participate in a separate study to continue receiving etavopivat. If/when this separate study becomes available, the participant may only transfer to the new study after completion of the 52-week primary treatment period and at any time during the 48-week optional extension treatment period.
Patient's parent, legal guardian, or legal representative has provided documented informed consent and patients have provided age-appropriate assent
12 to 16 years of age (inclusive) at time of screening
Confirmed diagnosis of SCD
TAMMV greater than or equal to (≥) 170 cm/s in the ICA and/or MCA during the Screening Period and confirmed on 2 occasions and without history of primary ischemic or hemorrhagic stroke, transient ischemic attack, or severe central nervous system (CNS) vasculopathy on magnetic resonance angiography (MRA). This includes patients with cTCD (170-199 centimeter per second [cm/s]) or aTCD (≥ 200 cm/s). Patients with aTCD cohort must have refused transfusion therapy.
Female who is breast feeding or pregnant
History of seizure disorder
Prior overt stroke (a focal neurological deficit of acute onset) by history or significant concerns for history of overt stroke based on Screening MRL, history of transient ischemic attack, focal neurological deficit on standardized neurological examination, or concern for moderate or severe neurological deficit (which could be due to stroke) based on a positive "10 questions" screening. Patients with significant or suggestive severe CNS vasculopathy (ie, moya moya) of Grade 4 or higher based on MRA read locally.
Significant cytopenias (absolute neutrophil count [ANC] < 1.5 × 10^3/microliter (µL), platelets < 150,000/µL, reticulocytes < 80,000/µL)