As shown in Fig. 4A, the top 10 enriched KEGG pathways for the down-regulated genes were PPAR signaling pathway; Retinol metabolism; Regulation of lipolysis in adipocytes; Malaria; Cocaine addiction; ECM − receptor interaction; Alanine, aspartate and glutamate metabolism; Wnt signaling pathway; Amphetamine addiction; and Adipocytokine signaling pathway. The gene discussed is PPARA; the disease is cocaine dependence.