SERPINA3 and Alzheimer disease: For the progression comparison (20 MCI vs. 20 AD cases), the leading candidate was Transcobalamin-1 (AUC 0.83, decreasing in AD samples—Supplementary Figure S3), which interestingly was also identified via the WGCNA analysis as a hub protein in the yellow module of saliva proteins downregulated with disease, as well as being involved in Vitamin B12 metabolism, alongside SAA1 and SERPINA3 (Table 3).