PCSK9 and familial hypercholesterolemia: In addition, a pathogenic mutation in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene has been proposed to cause FH, indicating that the disease is genetically heterogeneous.1–3 Several studies have demonstrated that mutations in the LDLR, APOB or PCSK9 genes can result in hypercholesterolemia.