Familial hypercholesterolemia (FH) is an autosomal disorder characterized by increased levels of total cholesterol and low density lipoprotein cholesterol. The FH clinical phenotype has been shown to be associated with increased coronary heart disease and premature death. Mutations in the low density lipoprotein receptor gene (LDLR) can result in the FH phenotype, and there is evidence that receptor-negative mutations result in a more severe phenotype than do receptor-defective mutations. Mutations in the apolipoprotein B-100 gene (APOB) can result in a phenotype that is clinically indistinguishable from familial hypercholesterolemia, and mutations in this gene have also been shown to be associated with coronary heart disease. Preliminary research indicates that the FH phenotype is influenced by other genetic and environmental factors; however, it is not clear if these are synergistic interactions or simply additive effects.