A recent meta-analysis (Munafo, Clark, Johnstone, Murphy, & Walton, 2004) examining the roles of many candidate genes and smoking behaviors suggested that individuals with at least one copy of the s allele of the 5-HTTLPR were less likely than those without to successfully quit smoking after behavioral treatment. Another study reported that individuals with at least one s allele and high levels of neuroticism were more nicotine dependent and more likely to report smoking to reduce negative affect than those with the l/l genotype and individuals with low levels of neuroticism (Hu et al., 2000). On the other hand, at least three studies have reported a positive association between the l allele of the 5-HTTLPR and smoking (versus never smoking; Ishikawa et al., 1999; Kremer et al., 2005; Arinami et al., 1999), or no relationship at all (David, Munafo, Murphy, Walton, & Johnstone, 2007; Trummer et al., 2006; Gonda et al., 2009; Rasmussen, Bagger, Tanko, Christiansen, & Werge, 2009). Another study demonstrated that smokers exhibited higher 5-HT transporter availability in the brainstem than non-smokers (Staley et al., 2001), an area in which 5-HT transporter function may be altered in individuals with mood disorders (Willeit et al., 2000).
