NPEPPS and Alzheimer disease: Figure 4A shows the scatter plot of the three candidate proteins, Heat shock 70 kDa protein 1A (HSPA1A), Puromycin-sensitive aminopeptidase (NPEPPS), and Prostaglandin F2 receptor negative regulator (PTGFRN). These proteins were differentially expressed, among the AD, MCI and CTRL groups, to a statistically significant degree. The PTGFRN shows a significant positive association with total plaque score and total tangle score (Figure 4B), suggesting its prediction potency of AD progression. Figure 4C shows the protein–protein interaction networks of HSPA1A, NPEPPS and PTGFRN identified by IPA.