Abstract
BackgroundApolipoprotein E is a glycoprotein best known as a mediator and regulator of lipid transport and uptake. The APOE-ε4 allele has long been associated with increased risks of Alzheimer's disease and mortality, but the effect of the less prevalent APOE-ε2 allele on diseases in the elderly and survival remains elusive.MethodsWe aggregated data of 38,537 individuals of European ancestry (mean age 65.5 years; 55.6% women) from six population-based cohort studies (Rotterdam Study, AGES-Reykjavik Study, Cardiovascular Health Study, Health-ABC Study, and the family-based Framingham Heart Study and Long Life Family Study) to determine the association of APOE, and in particular APOE-ε2, with survival in the population.ResultsDuring a mean follow-up of 11.7 years, 17,021 individuals died. Compared with homozygous APOE-ε3 carriers, APOE-ε2 carriers were at lower risk of death (hazard ratio,95% confidence interval: 0.94,0.90–0.99; P = 1.1*10−2), whereas APOE-ε4 carriers were at increased risk of death (HR 1.17,1.12–1.21; P = 2.8*10−16). APOE was associated with mortality risk in a dose-dependent manner, with risk estimates lowest for homozygous APOE-ε2 (HR 0.89,0.74–1.08), and highest for homozygous APOE-ε4 (HR 1.52,1.37–1.70). After censoring for dementia, effect estimates remained similar for APOE-ε2 (HR 0.95,0.90–1.01), but attenuated for APOE-ε4 (HR 1.07,1.01–1.12). Results were broadly similar across cohorts, and did not differ by age or sex. APOE genotype was associated with baseline lipid fractions (e.g. mean difference(95%CI) in LDL(mg/dL) for ε2 versus ε33: -17.1(-18.1–16.0), and ε4 versus ε33: +5.7(4.8;6.5)), but the association between APOE and mortality was unaltered after adjustment for baseline LDL or cardiovascular disease. Given the European ancestry of the study population, results may not apply to other ethnicities.ConclusionCompared with APOE-ε3, APOE-ε2 is associated with prolonged survival, whereas mortality risk is increased for APOE-ε4 carriers. Further collaborative efforts are needed to unravel the role of APOE and in particular APOE-ε2 in health and disease.
Highlights
Apolipoprotein E is a glycoprotein best known as a mediator and regulator of lipid transport and uptake, and has several additional physiological and pathological roles.[1]
Compared with homozygous APOE-ε3 carriers, APOE-ε2 carriers were at lower risk of death, whereas APOE-ε4 carriers were at increased risk of death (HR 1.17,1.12–1.21; P = 2.8*10−16)
After censoring for dementia, effect estimates remained similar for APOE-ε2 (HR 0.95,0.90–1.01), but attenuated for APOE-ε4 (HR 1.07,1.01–1.12)
Summary
Apolipoprotein E is a glycoprotein best known as a mediator and regulator of lipid transport and uptake, and has several additional physiological and pathological roles.[1] The APOE gene, on chromosome 19, contains four exons and codes for a 317 amino acid polypeptide that gives rise to a 299 amino acid long mature protein (34kD).[1] There are three circulating APOE isoforms designated APOE-ε4, -ε3, and -ε2, with corresponding allele frequencies of approximately 14%, 78%, and 8%, respectively.[2] Within the central nervous system, apolipoprotein E is produced mainly by astrocytes, while in peripheral tissue, it is expressed primarily in the liver and kidneys in addition to spleen, adrenals, and fatty tissue.[3,4]. The APOE-ε4 allele has long been associated with increased risks of Alzheimer’s disease and mortality, but the effect of the less prevalent APOE-ε2 allele on diseases in the elderly and survival remains elusive
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