To compare the safety, tolerability and LDL-C response after 24 Weeks of monthly (every 4 weeks [Q4W]) subcutaneous (SC) dosing of LIB003 300 mg with monthly (Q4W) SC dosing of 420 mg evolocumab (Repatha®) in patients with HoFH on stable diet and oral LDL-C-lowering drug therapy

Patients with verified HoFH on stable and continuing doses of oral lipid lowering therapy will be randomized to either evolocumab 420 mg Q4W or LIB003 300 mg Q4W for 24 weeks (Period A). At Week 24, subjects will be crossed over to LIB003 if they were on evolocumab and vice versa for the next 24 weeks (Period B).

Inclusion Criteria:

• HoFH diagnosed clinically and confirmed by genotyping
• Weight of >30 kg and body mass index (BMI) >17 and <40 kg/m2
• stable diet and lipid-lowering oral therapies for at least 4 weeks

Exclusion Criteria:

• mipomersen within 6 months of screening;
• LDL or plasma apheresis <2 months prior to randomization
• history of non-response to PCSK9 mAb or presence of receptor negative/null LDLR activity expected to result in non-response to PCSK9 inhibition
• prior or active clinical condition or acute and/or unstable systemic disease compromising subject inclusion

treatment is open label but lipid results are masked to participant, investigator and sponsor