A 52-year-old male shopkeeper from Delhi presents with chest pain on exertion for 3 months. He has a family history of premature coronary artery disease (father died of MI at age 55). Physical examination reveals xanthomas over the knuckles and Achilles tendons. Serum total cholesterol is 580 mg/dL, LDL-C 520 mg/dL, HDL-C 35 mg/dL, triglycerides 150 mg/dL. Genetic testing confirms homozygous familial hypercholesterolaemia (FH). Which of the following mechanisms best explains the severely elevated LDL cholesterol in this patient?