APOB and familial hypercholesterolemia: Familial hypercholesterolemia is characterized by the presence of one (HeFH) or two (HoFH) pathogenic variants in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), proprotein convertase subtilisin/kexin type 9 (PCSK9) or LDL-receptor adaptor protein 1 (LDLRAP1) genes, which cause very high levels of low-density lipoprotein (LDL) cholesterol (LDL-C) and premature atherosclerotic cardiovascular disease.