The purpose of this study is to evaluate the safety and tolerability of givosiran (ALN-AS1) in AIP patients as well as to characterize pharmacokinetics (PK) and pharmacodynamics (PD) of ALN-AS1 in AIP patients.

Parts A and B

Inclusion Criteria:

• Diagnosis of AIP
• Urine PBG at Screening indicating patient is a high excreter
• No clinically significant health concerns
• Women of child bearing potential must have a negative pregnancy test, not be nursing, and use effective contraception
• Willing to provide written informed consent and willing to comply with study requirements.

Exclusion Criteria:

• Porphyria attack within 6 months of screening
• Started a new prescription medication within 3 months of screening
• Clinically significant abnormal laboratory results
• Received an investigational agent within 90 days before the first dose of study drug or are in follow-up of another clinical study
• History of multiple drug allergies or intolerance to subcutaneous injection

Part C

Inclusion Criteria:

• Diagnosis of AIP
• Patient experienced a porphyria attack or was taking medication to prevent attacks recently
• No clinically significant health concerns
• Women of child bearing potential must have a negative pregnancy test, not be nursing, and use effective contraception
• Willing to provide written informed consent and willing to comply with study requirements.

Exclusion Criteria:

• Stared a new prescription medication within 3 months of screening
• Clinically significant abnormal laboratory results
• Received an investigational agent within 90 days before the first dose of study drug or are in follow-up of another clinical study
• History of multiple drug allergies or intolerance to subcutaneous injection