low-density lipoprotein (LDL) receptor disorder, an inherited disorder transmitted as a dominant trait and characterized by a high level of serum cholesterol, tendinous xanthomas, and early evidence of atherosclerosis, especially of the coronary arteries. Affected individuals at 50 years of age have 3 to 10 times greater risk of ischemic heart disease than the general population. Cholesterol levels are elevated at birth, increase with age, and average 250 to 500 mg/dL in heterozygous adults and 500 to 1000 mg/dL in adults who are homozygous for the gene. Xanthomas begin to appear at 20 years of age and occur most frequently on the Achilles tendon, extensor tendons of the hands, elbows, and tibial tuberosities. In type IIA familial hypercholesterolemia, only low-density lipoprotein (LDL) level is elevated, whereas in type IIB LDL and very low–density lipoprotein levels are increased. The disorder occurs in Caucasians, African-Americans, and Asian-Americans; the prevalence of the gene in the United States is 1:1000. Treatment includes a diet that is low in cholesterol and saturated fat. Cholestyramine may be given to patients with type IIA familial hypercholesterolemia but not to those with type IIB. Also called familial hypercholesterolemia, hypercholesterolemic xanthomatosis, hyperlipidemia type IIA, hyperlipidemia type IIB.
