Down-regulated differentially expressed genes are centrally enriched in KEGG, including Cytokine-cytokine receptor interaction pathway, MAPK signaling pathway, NF-κB signaling pathway, Hematopoietic cell lineage pathway, Dilated cardiomyopathy pathway, IL-17 signaling pathway, Antigen processing and presentation pathway, Primary immunodeficiency pathway, Nicotine addiction and Carbohydrate digestion and absorption pathway (Figure 1D). Here, NFKB1 is linked to nicotine dependence.