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 thalassemiagenotype

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 90days prior to signing the informed consent form (ICF) and/or assent form, and withno anticipated need for dose adjustments (other than weight based) or for initiationof 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 ICHguidelines.

Exclusion Criteria:

1. Body weight < 10kg at the screening visit

2. Hospitalization for VOC or acute chest syndrome (ACS) within the 14 days prior toexecution of informed consent/assent

3. More than 10 VOCs within the past 12 months that required hospitalization, emergencyroom, or clinic visit

4. Stroke resulting in focal neurological deficit; previous silent infarcts arepermitted.

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 28days 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 preventativetransfusion) or has received an RBC transfusion or exchange transfusion for anyreason within 90 days of signing the informed consent/assent