We note that as more researchers begin specifically looking for joint effects, the reports of interactions have increased. This is particularly true for genetic studies of smoking. In addition to the CGASP result mentioned above, several other studies have reported interesting results from the joint analysis of multiple loci chr15q25 in samples of European descent (Li et al. 2010a; Liu et al. 2010; Thorgeirsson et al. 2010; Tobacco and Genetics Consortium 2010), African Americans (Li et al. 2010a), and Koreans (Li et al. 2010b). Additional joint genetic effects related to smoking have been reported in other candidate regions, including interactions among variants in GABBR1 and GABBR2 related to nicotine dependence in African and European Americans (Li et al. 2009) and an interaction between CYP2A6 and MAOA affecting smoking in Chinese (Tang et al. 2009).
