As shown in Fig. 6b, the functional annotation of the 13 hub mRNAs showed that they were mainly enriched in skin development and regulation of B cell receptor signaling pathway in GO-BP, apical plasma membrane and postsynaptic membrane in GO-CC, transferase activity, transferring hexosyl/glycosyl groups in GO-MF, and glycosphingolipid biosynthesis related signaling pathways and Nicotine/Cocaine addiction in the KEGG pathway analysis. Here, PPIB is linked to cocaine dependence.