Protein phosphatase 1 catalytic subunit alpha (PPP1CA) and cathepsin D (CTSD) were validated as biomarkers, showing significant upregulation in T2DM samples and high diagnostic accuracy (AUC of PPP1CA = 0.969 and CTSD = 0.984 in the training cohort, AUC of PPP1CA = 0.806 and CTSD = 0.875 in the validation cohort, respectively). Here, CTSD is linked to type 2 diabetes mellitus.