PTPN22 and Alzheimer disease: Protein tyrosine phosphatase N22 (Ptpn22), an immune signaling regulator previously implicated in AD,86, 87 was the only other target gene that was significantly differentially expressed in both neuronal subpopulations at both time points (absolute log2FC > 0.2 with a Wald test padj < 0.05, Figure 4A,B).