PCSK9 and homozygous familial hypercholesterolemia: HoFH is most commonly caused by the occurrence of two LDL receptor (LDLR) gene mutations, but can also be caused by mutations in other genes that directly or indirectly act on the LDL/LDL-receptor pathway, including the genes encoding apolipoprotein B (apoB; APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and LDL-receptor adaptor protein 1 (LDLRAP1) [1].