PCSK9 and familial hypercholesterolemia: However, a recent large-scale study showed that the known genetic variants identified from familial hypercholesterolemia, including mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9), LDL receptor (LDLR) and apolipoprotein B (APOB), could only explain 2.5% of severe hypercholesterolemia cases [3].