In nutshell, we identified seven hub genes (HIST2H2AA3, HIST2H2AA4, NFKBIA, SESN2, SMURF1, TGFβ1, TNRC6A) in T2DM vs. PC, six common hub genes (ATP6V0D1, ATP6V0C, ATP6V0E1, CTSD, CYBA, TGFβ1) in T2DM vs. LC and five common hub genes (ALYREF, CDKN2D, NGDN, THRAP3, UBE2M) in T2DM vs. BC, respectively (Fig. 3). The gene discussed is CTSD; the disease is type 2 diabetes mellitus.