PCSK9 and familial hypercholesterolemia: Heterozygous mutations in LDL Receptor (Davis et al., 1986), Apolipoprotein B (Innerarity et al., 1987), PCSK9 (Abifadel et al., 2003), and Apolipoprotein E (Marduel et al., 2013) are linked to hypercholesterolemia.