GWAS have their limitations as well. Severe corrections for multiple testing must be applied when using atheoretical, large-scale approaches, resulting in the need for extraordinarily large numbers of participants. And candidate gene studies have not been abandoned entirely. In fact, it makes good sense to take advantage of what knowledge we do possess about the underlying biology and to further study genes involved in those systems. One of the most robust findings to come out of meta-analyses of GWAS for smoking behavior was to confirm the involvement of a set of candidate genes previously thought to play a role in susceptibility, the nicotine receptor genes (Caporaso et al., 2009). However, a critical difference is that most of the specific GxE interactions that have been studied have been limited to a single purportedly functional marker in a candidate gene of interest. The evidence for the functionality of these markers is often ambiguous (Cirulli & Goldstein, 2007), a factor that is not widely recognized by developmental psychologists. This is understandable as the methods of molecular biology go well beyond the expertise of
