PSEN1 and Alzheimer disease: Genome-wide association studies (GWAS) have identified several gene loci that influence the risk of AD and include the presenilin genes, PS1 and PS2, clusterin, complement receptor 1, ABCA7, PICALM, CD33, MS4A6A, MS4A4E, CD2AP, SOAT1, and PTGS2 [12,13].