vs. controls), brain tissue region (frontal, parietal, temporal, or cerebellar), postmortem interval, institute source of sample, and hybridization date, we evaluated the relationship between rs422112 and MAPT transcript expression levels. Across all cases and controls, we found a strong association between the T allele of rs422112 and decreased MAPT transcript expression levels (standardized β-coefficient = −0.27, t-statistic = −6.61, p-value = 1.45 × 10−10) which corresponds to presence of the A allele of rs393152 and increased MAPT transcript expression (Figure 3). Subgroup analyses demonstrated similar results within the AD cases and controls (see Supplemental Results). We further assessed the specificity of our findings by evaluating the relationship between the AD-PD pleiotropic locus and transcript levels of synaptophysin (SYP), a neuronal protein, and synuclein (SNCA), a neural protein associated with tau and PD. In contrast to MAPT transcript levels, we found no relationship between rs422112 and transcript levels of either SYP or SNCA (see Supplemental Results and Figure 3). We additionally performed a ‘locus wide association study’ testing all SNPs in the MAPT region for association with MAPT transcript expression levels. SNPs in r2 = 1.0 with rs393152 constituted the peak of the association signal (p < 1.0 ×10−8) with MAPT
