Most of the AD signature genes are skin barrier, or skin barrier modulator genes, including FLG2, LORICRIN, KRT31, LCE3A/C/D/E, S100A2/7/7A/8/9, CSTA, APOBEC3A, CNFN, and SPRR1B/2A/2B/2D/2E/2F/2G. This evidence concerns the gene FLG2 and Alzheimer disease.