Following the discovery that PCSK9 gain-of-function mutations were associated with familial hypercholesterolemia and loss-of-function mutations led to reduced levels of low-density lipoprotein cholesterol (LDL-C), PCSK9 rapidly became one of the most promising targets for modulating LDL-C levels [38, 39]. The gene discussed is PCSK9; the disease is familial hypercholesterolemia.