PCSK9 and Hypocholesterolemia: The development of a mouse model lacking PCSK9 specifically in hepatocytes (PCSK9 LivKO) indicated that the liver is responsible for two-thirds of the hypocholesterolemia observed in whole-body PCSK9-deficient mice (KO), suggesting that PCSK9 also controls cholesterol homeostasis through extrahepatic pathway(s) (6).