The 2nd extended PPI network without co-expression interactions demonstrated 16 nodes for the KEGG pathways52 of alcoholism (ARAF, ATF2, BRAF, CREB1, CREB5, FOSB, HDAC1, HDAC2, HDAC3, HIST2H2BE, HRAS, MAP2K1, MAPK1, MAPK3, RAF1, and SOS1), 7 nodes of amphetamine addiction (ATF2, CREB1, CREB5, FOS, FOSB, HDAC1, and JUN), and 7 nodes of cocaine addiction (ATF2, CREB1, CREB5, FOSB, JUN, NFKB1, and RELA) in Table 3. The gene discussed is HDAC2; the disease is cocaine dependence.