A Study to Evaluate ALN-CIDEB in Adult Participants With Metabolic Dysfunction-Associated Steatotic Liver Disease or With Metabolic Dysfunction-Associated Steatohepatitis (MASLD/MASH)

This study is researching an experimental drug called ALN-CIDEB, also referred to as "study drug". The study is focused on participants with metabolic dysfunction-associated steatotic liver disease (MASLD) (Part A) and metabolic dysfunction-associated steatohepatitis (MASH) (Part B). MASLD and MASH are long-lasting liver conditions caused by having too much fat in the liver. The aim of the study is to see how safe and tolerable the study drug is. The study is looking at several other research questions, including: * What side effects may happen from taking the study drug…

• Key Inclusion Criteria: 1. Part A: 18 to 55 years at Screening Visit 1 with MASLD, at Screening Visit 1 Part B: 18 to 65 years at Screening Visit 1 with a diagnosis of MASH, at Screening Visit 1 2. Body Mass Index (BMI) ≥30 kg/m2 and ≤40 kg/m2 at Screening Visit 1 3. Controlled-Attenuation Parameter (CAP) ≥285 dB/m by FibroScan during screening as described in the protocol 4. Liver fat content ≥8.5% by MRI-PDFF during screening 5. If on anti-hypertensive and/or lipid lowering medications and/or glucose lowering medications, must be on generally stable dose(s) for at least 12 weeks prior to screening and no changes to the dose(s) are anticipated during the study 6. Part B: A diagnosis of MASH documented in the participant's medical history, or a clinical suspicion of MASH based on non-invasive biomarkers (eg, evidence of fatty liver on imaging and elevated liver enzymes) and clinical risk factors, including having a history of 2 or more elements of metabolic syndrome, as defined in the protocol 7. Part B: Screening percutaneous liver biopsy NAFLD Activity Score (NAS) ≥3 and fibrosis stage, as defined in the protocol Key

Use the source registry for the full inclusion and exclusion criteria before discussing referral or enrolment.