familial hyperlipoproteinemia type II
Definition: hyperlipoproteinemia characterized by increased plasma levels of β-lipoproteins and cholesterol, elevated or normal levels of triglycerides; heterozygotes have mild lipid changes and are susceptible to atherosclerosis in middle age, but homozygotes have severe changes (often with generalized xanthomatosis, xanthelasma, corneal arcus, and frank clinical atherosclerosis as young adults). This disorder is divided into two classes, both inherited as autosomal dominant with homozygotes more severely affected than heterozygotes: type IIA, which is characterized by elevated LDL but normal triglycerides and is due to a deficiency of the LDL receptor, a defect of the receptor or a modified LDL-apolipoprotein B-100, caused by mutation in the LDL receptor (LDLR) gene on chromosome 19p. SYN familial hypercholesterolemia; type IIB has elevated LDL, cholesterol, and triglycerides, due to dysregulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), the rate-controlling enzyme in cholesterol biosynthesis. SYN familial hyperbetalipoproteinemia, familial hypercholesterolemic xanthomatosis.