APOLIPOPROTEIN E3 (APOE3)
[APOE_HUMAN] Defects in APOE are a cause of hyperlipoproteinemia type 3 (HLPP3) [MIM:107741]; also known as familial dysbetalipoproteinemia. Individuals with HLPP3 are clinically characterized by xanthomas, yellowish lipid deposits in the palmar crease, or less specific on tendons and on elbows. The disorder rarely manifests before the third decade in men. In women, it is usually expressed only after the menopause. The vast majority of the patients are homozygous for APOE*2 alleles. More severe cases of HLPP3 have also been observed in individuals heterozygous for rare APOE variants. The influence of APOE on lipid levels is often suggested to have major implications for the risk of coronary artery disease (CAD). Individuals carrying the common APOE*4 variant are at higher risk of CAD.     Genetic variations in APOE are associated with Alzheimer disease type 2 (AD2) [MIM:104310]. It is a late-onset neurodegenerative disorder characterized by progressive dementia, loss of cognitive abilities, and deposition of fibrillar amyloid proteins as intraneuronal neurofibrillary tangles, extracellular amyloid plaques and vascular amyloid deposits. The major constituent of these plaques is the neurotoxic amyloid-beta-APP 40-42 peptide (s), derived proteolytically from the transmembrane precursor protein APP by sequential secretase processing. The cytotoxic C-terminal fragments (CTFs) and the caspase-cleaved products such as C31 derived from APP, are also implicated in neuronal death. Note=The APOE*4 allele is genetically associated with the common late onset familial and sporadic forms of Alzheimer disease. Risk for AD increased from 20% to 90% and mean age at onset decreased from 84 to 68 years with increasing number of APOE*4 alleles in 42 families with late onset AD. Thus APOE*4 gene dose is a major risk factor for late onset AD and, in these families, homozygosity for APOE*4 was virtually sufficient to cause AD by age 80. The mechanism by which APOE*4 participates in pathogenesis is not known. Defects in APOE are a cause of sea-blue histiocyte disease (SBHD) [MIM:269600]; also known as sea-blue histiocytosis. This disorder is characterized by splenomegaly, mild thrombocytopenia and, in the bone marrow, numerous histiocytes containing cytoplasmic granules which stain bright blue with the usual hematologic stains. The syndrome is the consequence of an inherited metabolic defect analogous to Gaucher disease and other sphingolipidoses.   Defects in APOE are a cause of lipoprotein glomerulopathy (LPG) [MIM:611771]. LPG is an uncommon kidney disease characterized by proteinuria, progressive kidney failure, and distinctive lipoprotein thrombi in glomerular capillaries. It mainly affects people of Japanese and Chinese origin. The disorder has rarely been described in Caucasians.    Defects in APOE are a cause of familial hypercholesterolemia (FH) [MIM:143890]. FH is a condition characterized by elevated circulating cholesterol contained in either low-density lipoproteins alone or also in very-low-density lipoproteins. 
[APOE_HUMAN] Mediates the binding, internalization, and catabolism of lipoprotein particles. It can serve as a ligand for the LDL (apo B/E) receptor and for the specific apo-E receptor (chylomicron remnant) of hepatic tissues.
Publication Abstract from PubMed
The defective binding of apolipoprotein (apo) E2 to lipoprotein receptors, an underlying cause of type III hyperlipoproteinemia, results from replacement of Arg 158 with Cys, disrupting the naturally occurring salt bridge between Asp 154 and Arg 158. A new bond between Asp 154 and Arg 150 is formed, shifting Arg 150 out of the receptor binding region. Elimination of the 154-150 salt bridge by site-directed mutagenesis of Asp 154 to Ala restored the receptor binding activity to near normal levels. The X-ray crystal structure of apoE2 Ala 154 demonstrated that Arg 150 was relocated within the receptor binding region. Our results demonstrate that defective binding of apoE2 occurs by a novel mechanism of the replacement of one salt bridge with another.
Novel mechanism for defective receptor binding of apolipoprotein E2 in type III hyperlipoproteinemia.,Dong LM, Parkin S, Trakhanov SD, Rupp B, Simmons T, Arnold KS, Newhouse YM, Innerarity TL, Weisgraber KH Nat Struct Biol. 1996 Aug;3(8):718-22. PMID:8756331
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.