Apolipoprotein E ε4 prevalence in Alzheimer's disease patients varies across global populations: a systematic literature review and meta-analysis.

BACKGROUND: The ε4 allele of apolipoprotein E (APOE) is associated with Alzheimer's disease (AD). However, attributable risk due to APOE4 varies by region and by race/ethnicity. METHODS: A literature review and meta-analysis were conducted to estimate the prevalence of APOE4 by geographic area among AD patients. RESULTS: Although estimates varied significantly by study design and case definition, AD patients recruited in Asian and southern European/Mediterranean communities seemed to have significantly lower E4 carrier status estimates (37 and 43%) than those recruited in North America (58%) or northern Europe (64%; all: p < 0.05). CONCLUSIONS: APOE4 genotype frequency varies among AD patients in regional patterns similar to that of the general population. Study level differences may also contribute to the heterogeneity of published estimates of APOE4 in AD cases.