A Trial to Learn if ALN-PNP is Safe and Well Tolerated in Healthy Adults and Adult Participants With Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Key Inclusion Criteria:

Part A (Healthy Adults):

1. From 18 to 55 years of age

2. For Japanese cohorts ONLY; the Japanese participant must:

3. Be Japanese, born in Japan, and have both biologic parents and 4 biologicgrandparents who are ethnically Japanese and born in Japan

4. Have maintained a Japanese lifestyle, with no significant change since leavingJapan, including having access to Japanese food and adhering to a Japanese diet

5. Be living <10 years outside of Japan

6. Has a Body Mass Index (BMI) between 18 and 32 kg/m^2, inclusive, at the screeningvisit

7. Is judged by the investigator to be in good health, as described in the protocol

8. Is in good health based on laboratory safety testing obtained at the screening visitand approximately within 24 hours prior to administration of study drug

Part B and Part C (Participants with MASLD):

1. Part B: From 18 to 65 years of age

2. Part C: From 18 to 75 years of age

3. BMI from 23.0 kg/m2 to 40.0 kg/m2, inclusive, for East Asians (including but notlimited to South Koreans, Chinese, Taiwanese, and Japanese) and BMI from 27.0 kg/m2to 40.0 kg/m2, inclusive, for any other ethnicity at screening visit 1

4. Liver fat content ≥8.5% as measured by MRI-PDFF at screening visit 3

Key Exclusion Criteria:

Part A:

1. History of clinically significant cardiovascular, respiratory, hepatic, renal,gastrointestinal, endocrine, hematological, psychiatric, neurological, ordermatologic disease, as assessed by the investigator, that may confound the resultsof the study or poses an additional risk to the participant by study participation

2. Presents any concern to the study investigator that might confound the results ofthe study or poses an additional risk to the participant by their participation inthe study

3. Hospitalized for any reason within 30 days of the screening visit

4. Using the Modification of Diet in Renal Disease equation, has a glomerularfiltration rate as described in the protocol at the screening visit

5. Has Alanine Aminotransferase (ALT) or Aspartate Aminotransferase (AST) or totalbilirubin above the Upper Limit of Normal (ULN) range

6. Is a current smoker or former smoker, including e-cigarettes, who stopped smokingwithin 3 months prior to the screening visit

7. Has a history of alcohol or drug abuse per investigator opinion

8. Is positive for hepatitis C antibody and if so, positive for qualitative (ie,detected or not detected) Hepatitis C Virus (HCV) Ribonucleic Acid (RNA) test at thescreening visit

Part B and Part C:

1. Evidence of other forms of known chronic liver disease, as defined in the protocol

2. Has a contraindication to MRI examinations, as defined in the protocol

3. History of Type 1 diabetes

4. Has lost or gained more than 4.0% body weight over the 3 months prior to or duringthe screening period

5. Has known Human Immunodeficiency Virus (HIV) infection, evidence of current orchronic Hepatitis B Virus (HBV) infection, or current or chronic HCV infection, asdefined in the protocol

6. Bariatric surgery within approximately 5 years (Part B) or 3 years (Part C) prior orplanned during the study period

NOTE: Other protocol defined inclusion / exclusion criteria apply