Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease

Eleven susceptibility loci for late-onset Alzheimer's disease (LOAD) were identified by previous studies; however, a large portion of the genetic risk for this disease remains unexplained. We conducted a large, two-stage meta-analysis of genome-wide association studies (GWAS) in individuals of European ancestry. In stage 1, we used genotyped and imputed data (7,055,881 SNPs) to perform meta-analysis on 4 previously published GWAS data sets consisting of 17,008 Alzheimer's disease cases and 37,154 controls. In stage 2, 11,632 SNPs were genotyped and tested for association in an independent set of 8,572 Alzheimer's disease cases and 11,312 controls. In addition to the APOE locus (encoding apolipoprotein E), 19 loci reached genome-wide significance (P < 5 × 10(-8)) in the combined stage 1 and stage 2 analysis, of which 11 are newly associated with Alzheimer's disease.

APOE and Alzheimer disease: a major gene with semi-dominant inheritance

Apolipoprotein E (APOE) dependent lifetime risks (LTRs) for Alzheimer Disease (AD) are currently not accurately known and odds ratios alone are insufficient to assess these risks. We calculated AD LTR in 7351 cases and 10 132 controls from Caucasian ancestry using Rochester (USA) incidence data. At the age of 85 the LTR of AD without reference to APOE genotype was 11% in males and 14% in females. At the same age, this risk ranged from 51% for APOE44 male carriers to 60% for APOE44 female carriers, and from 23% for APOE34 male carriers to 30% for APOE34 female carriers, consistent with semi-dominant inheritance of a moderately penetrant gene. Using PAQUID (France) incidence data, estimates were globally similar except that at age 85 the LTRs reached 68 and 35% for APOE 44 and APOE 34 female carriers, respectively. These risks are more similar to those of major genes in Mendelian diseases, such as BRCA1 in breast cancer, than those of low-risk common alleles identified by recent GWAS in complex diseases. In addition, stratification of our data by age groups clearly demonstrates that APOE4 is a risk factor not only for late-onset but for early-onset AD as well. Together, these results urge a reappraisal of the impact of APOE in Alzheimer disease.

APOE genotype, cholesterol level, lipid-lowering treatment, and dementia: the Three-City Study

OBJECTIVE

To examine the association of plasma cholesterol levels, lipid-lowering agent (LLA) intake, and APOE genotype with dementia prevalence.

METHODS

The Three-City Study is a population-based cohort of 9,294 subjects selected from the electoral rolls of three French cities (Bordeaux, Dijon, Montpellier). Baseline examination included extensive assessment of exposure to vascular risk factors (including cholesterol levels and LLA use [statin or fibrate]) and clinical diagnosis of dementia.

RESULTS

Two percent of participants were demented at baseline. Overall 32.4% of participants had hyperlipidemia, and 15.6% were prescribed statins and 13.7% fibrates. After adjusting for age, gender, education level, and study center, the odds ratio (OR) for dementia was observed to be lower among LLA users (OR = 0.61, 95% CI = 0.41 to 0.91) compared with subjects taking no LLAs. There was no differential effect between statin and fibrate users. The odds for dementia were increased in subjects with hyperlipidemia (OR = 1.43, 95% CI = 1.03 to 1.99). Further adjustment for potential confounders did not modify these associations. In addition, the association between LLA intake and dementia was not modified by APOE genotype, whereas hyperlipidemia was significantly associated with increased dementia prevalence only in non-epsilon4 carriers and non-Alzheimer disease cases. Finally, in participants taking LLAs, the odds for dementia were decreased only in those having normal lipid levels.

CONCLUSIONS

This observational study provides further evidence that lipid-lowering agents are associated with decreased risk of dementia, whereas hyperlipidemia is associated with increased odds for non-Alzheimer-disease-type dementia. These effects appear to be independent of all major potential confounders.