Study to Evaluate the Effect of GBT440 on TCD in Pediatrics With Sickle Cell Disease

Inclusion Criteria:

1. Male or female participants with Sickle Cell Anemia (SCA) HbSS, HbSβ0 thalassemia genotype
2. TCD time averaged maximum of the mean velocity (TAMMV) arterial cerebral blood flow ≥ 170 to 200cm/sec during the Screening Period
3. Hb ≥ 5.5 and ≤ 10.5 g/dL during screening
4. For participants taking HU, the dose of HU (mg/kg) must be stable for at least 90 days prior to signing the informed consent form (ICF) and/or assent form, and with no anticipated need for dose adjustments (other than weight based) or for initiation of HU for non-chronic use during the study, in the opinion of the Investigator
5. Written informed parental/guardian consent and participant assent (where applicable) has been obtained per IRB/EC policy and requirements, consistent with ICH guidelines.

Exclusion Criteria:

1. Body weight < 10kg at the screening visit
2. Hospitalization for VOC or acute chest syndrome (ACS) within the 14 days prior to execution of informed consent/assent
3. More than 10 VOCs within the past 12 months that required hospitalization, emergency room, or clinic visit
4. Stroke resulting in focal neurological deficit; previous silent infarcts are permitted.
5. Known history or findings suggestive of significant cerebral vasculopathy
6. History of seizure disorder
7. Has been treated with erythropoietin or other hematopoietic growth factors within 28 days of signing informed consent/assent or if, in the opinion of the Investigator, there is an anticipated need for such agents during the study
8. RBC transfusion therapy (also termed chronic, prophylactic, or preventative transfusion) or has received an RBC transfusion or exchange transfusion for any reason within 90 days of signing the informed consent/assent