The first GWAS for Alzheimer’s disease of 1086 individuals was done in 2007, and only replicated the previous association with APOE.30 Increasing sample sizes from new studies and meta–analysis of existing studies led to the discovery of novel Alzheimer’s disease loci,30 leading to the landmark meta–analysis done by the International Genomics of Alzheimer’s Project (IGAP) in 2013.5 This was the largest Alzheimer’s disease GWAS at the time and was a meta–analysis of earlier GWAS done by the European Alzheimer Disease Initiative, Genetic and Environmental Risk in Alzheimer’s Disease, Cohorts for Heart and Aging Research in Genomic Epidemiology, and the Alzheimer Disease Genetics Consortium. IGAP’s stage 1 discovery phase consisted of 17 008 Alzheimer’s disease cases and 37 154 controls (n=54 162, approximately 8% of cases and controls with pathology confirmed), with stage 2 consisting of a follow–up of the top 11 632 SNPs in an additional 8572 Alzheimer’s disease cases and 11 312 controls (n=74 046). The meta–analysis of stage 1 and stage 2 identified 19 Alzheimer’s disease susceptibility loci.
