LDLR and familial hypercholesterolemia: Familial hypercholesterolemia (FH) constitutes the most common inherited lipid disorder caused by mutations in any of the genes involved in the metabolism of low-density lipoprotein (LDL), including the LDL receptor (LDLR), Apolipoprotein B (APOB), or Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9).