Several functional variants in the CYP2B6 gene have also been identified. These include CYP2B6*4 (A785G; increased activity) (Lang et al., 2001), CYP2B6*9 (G516T; increased activity) (Ariyoshi et al., 2001), CYB2B6*5 (C1459T; decreased protein and enzyme activity) (Lang et al., 2001; Miksys et al., 2003), and CYP2B6*6 (G516T and A785G; structurally altered enzyme with little impact on peripheral nicotine metabolism) (Lee et al., 2007b) (http://www.cypalleles.ki.se/cyp2b6.htm). There is a distinct role of the CYP2B6 enzyme in the metabolism of the smoking-cessation medication, bupropion (Faucette et al., 2000), and the prevalent CYP2B6*6 variant is associated with slower bupropion metabolism (Hesse et al., 2004); however, it may increase the metabolism of other substrates (Jinno et al., 2003; Xie et al., 2003).
