Given that humans with loss-of-function mutations in the PCSK9 gene[12] and mice lacking Pcsk9 expression exhibit significantly reduced circulating LDL cholesterol levels[13], whereas activating mutations in the PCSK9 gene result in severe familial hypercholesterolemia[14] accompanied by increased cardiovascular risk, PCSK9 is considered at present to be an important therapeutic target for combating hypercholesterolemia[15]. Here, PCSK9 is linked to familial hypercholesterolemia.