APOE and Alzheimer disease: Figure 4 illustrates the associations between CSF PTPRS protein levels and key AD pathological biomarkers [P-Tau, T-Tau, Aβ42, T-Tau/Aβ42 ratio] following stratification by APOE4. Only T-Tau (R2 = 0.08, p < 0.05) and p(181)Tau (R2 = 0.06, p < 0.05) displayed significant associations in APOE4-negative subjects.