APOB and familial hypercholesterolemia: Familial hypercholesterolemia (FH) results from either heterozygous or homozygous mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), or proprotein convertase subtilisin/kexin type 9 (PCSK9) genes, leading to significantly elevated low-density lipoprotein cholesterol (LDL-C) levels, generally in a pattern of autosomal dominance.