MAPT and Alzheimer disease: SNP rs4420638 is the most significant AD-associated SNP in our QTL analysis for Aβ42 (FDR = 5.47E-15), T-tau/Aβ42 ratio (FDR = 4.28E-23), and p-tau/Aβ42 ratio (FDR = 1.78E-21; Figure 2 and Table 1).