A Study of ALN-PCSSC in Participants With Homozygous Familial Hypercholesterolemia (HoFH)

Inclusion Criteria:

- Males and females, ≥12 years of age with a diagnosis of homozygous familial
hypercholesterolemia by genetic confirmation or a clinical diagnosis based on a
history of an untreated low-density lipoprotein cholesterol (LDL-C) concentration >500
mg/deciliter (dL) [13 millimoles/liter (mmol/L)] together with either xanthoma before
10 years of age or evidence of heterozygous familial hypercholesterolemia in both
parents.

- Stable on a low-fat diet.

- Stable on pre-existing, lipid-lowering therapies (such as statins,
cholesterolabsorption inhibitors, bile-acid sequestrants, or combinations thereof) for
at least 4 weeks with no planned medication or dose change for the duration of study
participation.

- Fasting central lab LDL-C concentration >130 mg/dL (3.4 mmol/L) and triglyceride
concentration <400 mg/dL (4.5 mmol/L).

- Body weight of 40 kilograms (kg) or greater at screening.

Exclusion Criteria:

- LDL or plasma apheresis within 8 weeks prior to the screening visit, and no plan to
receive it during the study because of the attendant difficulty in maintaining stable
concentrations of LDL-C while receiving apheresis.

- Use of mipomersen or lomitapide therapy within 5 months of screening.

- Previous treatment with monoclonal antibodies directed towards PCSK9 within 8 weeks of
screening.

The above information is not intended to contain all considerations relevant to a
participant's potential participation in a clinical trial.