The purpose of this study is to investigate the pharmacokinetics and safety of a single dose of VX-770 in subjects with moderate hepatic impairment.

Inclusion Criteria:

Group A (Subjects with Hepatic Impairment):

• male or female between 18 and 65 years of age
• subjects must have a Child-Pugh total score of 7 to 9
• subjects must agree to use 1 highly effective method of contraception during the study and for 90 days after the completion of the study
• subjects must have a body mass index (BMI) of 18 to 35 kg/m2

Group B (Healthy Subjects):

• male or female between 18 and 65 years of age
• subjects will match subjects with hepatic impairment for sex, BMI, cigarette smoking habit, and age
• subjects must agree to use 1 highly effective method of contraception during the study and for 90 days after the completion of the study

Exclusion Criteria:

Group A (Subjects with Hepatic Impairment):

• subjects who are not clinically stable or who have a history of any illness that, in the opinion of the investigator or the subject's general practitioner, might confound the results of the study or pose an additional risk in administering study drug(s) to the subject
• subjects who are unwilling or unable to discontinue use of any inhibitors or inducers of CYP3A
• subjects who have a history of alcohol abuse within 1 year or illicit drug abuse within 2 years
• subjects who smoke more than 10 cigarettes per day
• subjects who have fluctuating or rapidly deteriorating hepatic function
• subjects who have significant renal dysfunction
• subjects who have HIV, or active hepatitis B
• subjects who have previous solid organ or bone marrow transplantation

Group B (Healthy Subjects):

• subjects who have a history of any illness that, in the opinion of the investigator or the subject's general practitioner, might confound the results of the study or pose an additional risk in administering study drug(s) to the subject
• subjects who are unwilling or unable to discontinue use of any inhibitors or inducers of CYP3A
• subjects who have a history of alcohol or illicit drug abuse within 2 years
• subjects who smoke more than 10 cigarettes per day
• subjects who have HIV, hepatitis C, or active hepatitis B