Clearly, results are conflicting across the six studies of 5-HTTLPR genotype and cannot be considered replications, even in a very broad sense. Research on life stress and 5-HTTLPR genotype interactions in alcohol-related outcomes is marked by wide variation in the conceptualization of stressors and drinking outcomes, so the variable-defined space they cover is fairly non-overlapping. Researchers inconsistently used a variant-based linear model (i.e., coding 0, 1 or 2 risk variants) versus a genotypic model (i.e., coding genotypes into 2 or 3 nominal categories), and the “risk” genotype varied across studies. To our knowledge, only one of the studies reviewed here (Laucht et al., 2009) distinguished between the two forms of the L allele, potentially reducing power of the others to detect GxE.
