An important decision in the analysis of G×E is the selection of a genetic model. Each individual carries two copies of the serotonin transporter gene, and each of these two copies may contain either the more common long variant or the less common short variant, resulting in three possible genotypes: long–long (LL), long–short (LS), and short–short (SS). Although there is agreement that the short variant confers sensitivity to the depressogenic effects of adversity, studies differ in whether one or two short alleles are needed (i.e. whether the “sensitivity” effect is dominant or recessive) or whether the sensitivity increases gradually with the number of short alleles (i.e., an additive genetic model). A synthesis of current evidence does not support any of the genetic models above the others (Caspi et al., 2010; Uher and McGuffin, 2008) and it has been suggested that all three genetic models should be tested and reported in studies of G×E in order to build a transparent, cumulative database (Uher and McGuffin, 2008). Therefore, we test and report the results of additive, recessive and dominant genetic models.
