PCSK9 is a proprotein convertase which is involved in the degradation of low-density lipoprotein (LDL) receptors in the liver. Mutations in the PCSK9 gene cause familial hypercholesterolaemia in a subset of patients by reducing the number of LDL receptors on the surface of hepatocytes. This decreases their ability to clear LDL cholesterol from plasma. Conversely, other PCSK9 mutations result in unusually low concentrations of plasma LDL cholesterol and a reduced risk of atherosclerotic disease. Blocking the activity of PCSK9 with monoclonal antibodies reduces the degradation of LDL receptors and increases the clearance of LDL cholesterol. An injection of PCSK9-specific antibody suppresses LDL-cholesterol concentrations for several weeks. © 2016, Australian Government Publishing Service. All Rights reserved.