A Phase 1, multiple center, nonrandomized, open-label, parallel group study of a single oral dose of GBT440 administered in subjects with mild (Child-Pugh A), moderate (Child-Pugh B), or severe (Child-Pugh C) hepatic impairment disease and healthy subjects with normal hepatic function.

Approximately 24 to 28 subjects will be enrolled. Safety and PK assessments will be performed at selected time points throughout the study.

Inclusion Criteria:

All subjects:

• Males or females, 18 to 75 years old
• Willing and able to give written informed consent

Patients with hepatic impairment:

• Mild hepatic impairment (Child-Pugh A [5-6 points])
• Moderate hepatic impairment (Child-Pugh B [7-9 points])
• Severe hepatic impairment (Child-Pugh C [10-15 points])

Healthy subjects:

• Match in age, gender and body mass index with hepatic impaired subjects
• Healthy and without clinically significant abnormalities in vital signs, ECGs, physical exam, clinical laboratory evaluations, medical and surgical history

Exclusion Criteria:

All subjects:

• Participation in another clinical trial of an investigational drug (or medical device) within 30 days of the last dose of investigational drug or 5 half-lives whichever is longer, prior to screening, or is currently participating in another trial of an investigational drug (or medical device)
• Any signs or symptoms of acute illness at screening or Day -1
• History or presence of clinically significant allergic, hematological, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, or neurological disease

Patients with hepatic impairment:

• History of liver transplantation, hepatic mass suggestive of hepatocellular carcinoma or acute liver disease
• Screening serum ALT or AST >5 times the upper limit of normal