A Study of Enlicitide Decanoate (MK-0616, an Oral PCSK9 Inhibitor) in Children and Adolescents With Heterozygous Familial Hypercholesterolemia (MK-0616-029)

This study is designed to learn if enlicitide decanoate is safe and effective to treat children and adolescents with heterozygous familial hypercholesterolemia (HeFH) and high amounts of low-density lipoprotein cholesterol (LDL-C) in the blood. The goals of this study are to learn about the safety of enlicitide and if children tolerate it, what happens to enlicitide in a child's body over time, and if enlicitide works to lower cholesterol levels in children more than a placebo.

Inclusion Criteria: Inclusion criteria include, but are not limited to: * Has possible or definite diagnosis of HeFH based on a locally accepted diagnostic algorithm or diagnosis by genetic testing results * Has a fasted LDL-C value (evaluated by the central laboratory) that is ≥130 mg/dL * Is receiving either an optimized daily dose of statin (± nonstatin LLT); or a nonstatin LLT with documented intolerance to at least 2 different statins or refusal of statin therapy by the participant or legally acceptable representative * Is on a stable dose of all background LLTs for at least 30 days prior to screening, with no medication or dose changes planned during participation in Part A or Part B Exclusion Criteria: Exclusion criteria include, but are not limited to: * Has a history of homozygous FH based on genetic or clinical criteria, or history of known compound heterozygous FH, or double heterozygous FH * Has a history of nephrotic syndrome * Has any clinically significant malabsorption condition based on principal investigator assessment * Was previously treated/is being treated with certain other cholesterol lowering medications, including proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors without adequate washout