RP9 and Alzheimer disease: After data preprocessing and differential expression analysis, we identified 1988 DEPs between AD and healthy controls (|Fold change| ≥ 1.2 and p-value < 0.05), including 723 upregulated (DNAJC8, IGLC1, LGALS1, ICAM4, and TRA2A) and 1,265 downregulated proteins (EDC3, HRH1, RP9, IL9, and HOXA1) (Figure 2A).