This is a Phase 3 single-arm, open-label, international, multi-center clinical trial to evaluate the efficacy and safety of lomitapide in pediatric patients with HoFH who are receiving stable lipid-lowering therapy, including LDL apheresis. The study is comprised of a 12-week Run-in Period, a primary 24-week Efficacy Phase, followed by an 80-week Safety Phase.

Inclusion Criteria:

1. Male or female aged ≥5 and <18 years with diagnosed functional HoFH
2. Patient must weigh at least 15 kg and be at or above the 10th percentile in BMI and at least 10th percentile in height for age and gender based on CDC growth charts
3. Negative pregnancy test at Screening and during the study for females of child bearing age
4. Potentially sexually active female patients who are of child-bearing age must either be sexually abstinent or follow two acceptable methods of contraception

Exclusion Criteria:

1. Other forms of primary hyperlipoproteinemia and secondary causes of hypercholesterolemia (e.g., nephrotic syndrome, hypothyroidism).
2. Abnormal liver function test at Screening
3. Moderate or severe hepatic impairment or active liver disease
4. Serum creatine phosphokinase (CPK) level >2 × ULN.
5. Chronic renal insufficiency
6. History of drug abuse within the last 3 years or habitual alcohol consumption
7. New York Heart Association (NYHA) Class III or IV congestive heart failure.
8. Uncontrolled hypertension
9. In the judgment of the PI, precocious or delayed puberty or endocrine disorder that would affect growth
10. History of non-skin malignancy or other cancers occurring within the past 3 years
11. History of inflammatory bowel disease or other malabsorption syndrome or a history of bowel resection, gastric bypass, or other weight loss surgical procedure.
12. Use of mipomersen within 6 months of Screening.
13. Any medical condition for which the life expectancy is predicted to be less than 5 years.
14. Any patient who is unable to avoid treatment with strong or moderate cytochrome P450 3A4 (CYP3A4) inhibitors, or other drugs contraindicated for use with lomitapide during the study.
15. Participation in an interventional clinical study within 6 weeks for a statin therapy or within 6 months for any other unapproved therapy.