Apolipoprotein E allelic frequency in elderly smokers.

Susceptibility genes for human diseases (e.g., cancer and atherosclerosis) increase disease risk by altering the metabolic activation of exogenous (e.g., carcinogens) and endogenous (e.g., cholesterol) compounds. The function of these genes, and subsequent risk, can be adversely affected by polymorphisms. This study tests the hypothesis that if specific genetic polymorphisms are related to mortality, then in elderly heavy smokers, there should be a decreased frequency of "at risk" alleles and an increased frequency of "protective" alleles, i.e., a survival effect. One such potential polymorphism is in the apolipoprotein E (apoE) gene, which is involved in cholesterol metabolism, where the epsilon4 allele is associated with an increased risk of coronary artery disease and is under represented in elderly populations. In this study, ApoE variant alleles were determined in 81 living, elderly current smokers (mean age: 72.5; range: 65-94; mean pack-years: 78; range: 13-192) and in 82 younger autopsy donors (mean age: 33; range: 1-58). There was a borderline difference in the apoE 4 allelic frequencies among the groups (11% in the elderly and 18% in the comparable younger group [df = 1; chi(2) = 4.02; P = 0.05]). A significant difference was found for age when stratified as a continuous variable by genotype in the elderly smokers (P = 0.03; mean age for persons with and without epsilon4 was 69.9 and 73.2, respectively). Pack-years of cigarette smokers did not differ by genotype, indicating no selective effect. These results confirm earlier associations for differences in the apoE allelic frequencies in the elderly and extend it to smokers, who generally have increased mortality at younger ages.