This study is researching an experimental drug called ALN-PNP. This study is focused on participants who are known to have nonalcoholic fatty liver disease (NAFLD), and a specific variant of the patatin-like phospholipase domain containing 3 (PNPLA3) gene.

The aim of this study is to see how safe, tolerable, and effective the study drug is.

This study is looking at several other research questions, including:

• What side effects may happen from taking the study drug
• How the study drug works to change liver fat content in NAFLD
• How much study drug and study drug metabolites (byproduct of the body breaking down the study drug) are in your blood at different times
• Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)
• Better understanding of the study drug and NAFLD

Key Inclusion Criteria:

1. Participants from 18 (or country's legal age of adulthood) to 65 years of age, inclusive, at screening visit 1
2. Body mass index (BMI) from 23.0 kg/m^2 to 40.0 kg/m^2, inclusive, for East Asians (including but not limited to South Koreans, Chinese, Taiwanese, and Japanese) and BMI from 27.0 kg/m^2 to 40.0 kg/m^2, inclusive, for any other ethnicity at screening visit 1
3. Meets genotype criteria for the rs738409:G PNPLA3 risk allele: homozygotes (for Part A and Part B) or heterozygotes (optional Part C); p.I148M variant (PNPLA3 rs738409:G [p.I148M]) at screening visit 1
4. Liver fat content ≥8.5% as measured by MRI-PDFF at screening visit 3
5. Generally stable diet (based on participant's recall) for at least 3 months prior to the screening visit

Key Exclusion Criteria:

1. Evidence of other forms of known chronic liver disease, as defined in the protocol
2. Has a contraindication to MRI examinations, such as persons with cardiac pacemaker and implants made out of metal (for example, cochlear implant, nerve stimulators, magnetic vascular clips, and metallic heart valve), severe claustrophobia, or other contraindications for MRI
3. Is taking a medication to treat a co-morbid condition that is not permitted during the study
4. Has any laboratory parameter assessments at screening, as defined in the protocol
5. History of Type 1 diabetes
6. Bariatric surgery within approximately 5 years prior or planned during the study period
7. Has lost or gained more than 4.0% body weight over the 3 months prior to or during the screening period
8. Has known human immunodeficiency virus (HIV) infection, evidence of current or chronic hepatitis B virus (HBV) infection, or current or chronic hepatitis C virus (HCV) infection, as defined in the protocol
9. Was hospitalized (ie, >24 hours) for any reason within 30 days of the screening visit

Note: Other protocol defined Inclusion/Exclusion Criteria apply

All Individual Patient Data (IPD) that underlie publicly available results will be considered for sharing.

When Regeneron has:

• received marketing authorization from major health authorities (e.g., FDA, European Medicines Agency (EMA), Pharmaceuticals and Medical Devices Agency (PMDA), etc.) for the product and indication or has globally discontinued development of the product for all indications on or after April 2020 and has no plans for future development
• made the study results publicly available (e.g., scientific publication, scientific conference, clinical trial registry)
• the legal authority to share the data, and
• ensured the ability to protect participant privacy

Qualified researchers can submit a proposal for access to individual patient or aggregate level data from a Regeneron-sponsored clinical trial through Vivli. Regeneron's Independent Research Request Evaluation Criteria can be found at: https://www.regeneron.com/sites/default/files/Regeneron-External-Data-Sharing-Policy-and-Independent-Research-Request-Evaluation-Criteria.pdf