Familial hypercholesterolemia (FH) is an inherited disorder characterized by a high concentration of serum LDL cholesterol. The high LDL cholesterol level frequently gives rise to xanthomas, deposits of cholesterol in peripheral tissues, and accelerated atherosclerosis resulting from cholesterol deposition in the arterial wall, thereby increasing the risk of premature coronary heart disease (CHD).1 The precise mode of inheritance was difficult to establish in regions where noninherited hypercholesterolemia was common, and was first defined by Khachadurian in 1964 in Lebanese FH pedigrees.2 Khachadurian showed that individuals from affected families could be segregated into three clear groups on the basis of their plasma cholesterol concentrations: presumed homozygotes with levels four times higher than normal; heterozygotes with levels two times higher that normal; and unaffected individuals. He concluded that FH was inherited as a monogenic autosomal codominant trait—a dominant disorder with a gene–dosage effect. The frequency of heterozygous FH in most populations is about 1/500,1 so homozygous FH is rare (less than or equal to1/106) in European populations with a low rate of consanguineous marriage, but the pattern of inheritance observed by Khachadurian can also be seen in small families of this origin