A Study of ALN-HSD in Healthy Adult Subjects and Adult Patients With Nonalcoholic Steatohepatitis (NASH)

Inclusion Criteria: * Part A Only * Has body mass index (BMI) ≥18 kg/m\^2 and ≤28 kg/m\^2 * Has normal 12-lead electrocardiogram (ECG) * Parts B and C Only: * Has BMI ≥18 kg/m\^2 and ≤40 kg/m\^2 * Has a diagnosis of NASH documented in the patient's medical history or a clinical suspicion of NASH based on defined study criteria * Has screening liver biopsy with NASH activity score (NAS) score of ≥3 per NASH Clinical Research Network (CRN) criteria Exclusion Criteria: * Parts A, B and C: * Has any clinical safety laboratory result considered clinically significant and unacceptable by the Investigator * Has known active human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV) infection * Has known history or evidence of drug abuse, within 12 months prior to screening * Has evidence of other forms of known chronic liver disease * Has recently received an investigational agent * Has any uncontrolled or serious disease, medical or surgical condition that my interfere with participation or data interpretation * Has excessive alcohol intake for ≥ 3 months during past year * Has history of intolerance to SC injection(s) * Has international normalized ratio (INR) \>1.2 * Has platelet count \<140x10\^9/L * Part A Only * Has systolic blood pressure (BP) \>140 mmHg and diastolic \>90 mmHg; * Has used certain prescription drugs within last 14 days prior to screening * Has used certain over the counter (OTC) medication within 7 days prior to screening * Has estimated glomerular filtration rate (GFR) \<90 mL/min/1.73m\^2 at screening * Parts B and C Only * Has abnormal ECG * Has changes in certain prescription medications defined in the protocol within the specified timeframe prior to screening * Has GFR\<45ml/min/1.73m\^2