PCSK9 and homozygous familial hypercholesterolemia: Although a small proportion of HoFH cases is caused by mutations in apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9), and low-density lipoprotein receptor adaptor protein 1 (LDLRAP1) [2], the most predominant form of HoFH is attributed to the inheritance of two copies of low-density lipoprotein receptor (LDLR) null mutant genes [3].