SPCS1 and major depressive disorder: Finally, the five interaction genes were screened by the four machine learning algorithms, namely integrin subunit beta 5 (ITGB5), signal peptidase complex subunit 1 (SPCS1), protein tyrosine kinase 2β (PTK2B), ribosomal protein S16 (RPS16) and ribosome production factor 2 homologue (RPF2), which were regarded as candidate biomarkers for AD with depression (Figure 7E and Table S8).