APOB and familial hypercholesterolemia: The risk of coronary heart disease and myocardial infraction is increased by the appearance of autosomal dominant hypercholesterolemia, which occurs in three forms: (1) familiar hypercholesterolemia resulting from a mutation in the LDLR gene, (2) familial defective apolipoprotein B resulting from a mutation in the APOB gene, and (3) hypercholesterolemia, autosomal dominant, 3, which is caused by one of three missense mutations in the PCSK9 gene.