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The association between apolipoprotein E allele epsilon 4 and late-onset Alzheimer's disease: pathogenic relationship or differential survival bias.

Recent genetic epidemiological studies 1-3 have documented a significant association between the apolipoprotein E (ApoE) allele e4 (ApoE-e4) and late-onset familial and sporadic Alzheimer's disease (AD). This association is so impressive that one group of investigators concluded that "homozygosity for ApoE-e4 was virtually sufficient to cause AD by age 80." 1 However, the bane of any epidemiological association is bias. 4 We suggest that selection bias may have significantly contributed to, or even produced, the observed association between ApoE-e4 and late-onset AD. The three common ApoE alleles are e2, e3, and e4. The relative frequencies of these alleles in healthy population samples are about 8%, 76%, and 14%, respectively. 5-6 Individuals with ApoE-e4 have an increased risk of premature coronary artery disease. 7-9 As a result of earlier mortality due to heart disease, the relative frequency of the e4 allele was predicted, and found, to decline with age. 10-11 This