ABCG2 and nicotine dependence: We also noted depletion of Type VI secretion systems (Log2FoldChange − 1.99, P. adjusted value < 0.00027), Rrf2 family transcriptional regulators (Log2FoldChange − 0.598, P. adjusted value < 0.00067), and ABC transporter oligopeptide (TC 3.A.1.5.1) (Log2FoldChange -0.351, P. adjusted value < 0.00001) in the more nicotine dependence group (Fig. 4).