We also encourage family researchers to consider polygenic approaches in future studies of GxE. Polygenic approaches include the effects of many variants of small magnitude across the genome (Plomin, Haworth, & Davis, 2009). Considering multiple genes and variants in aggregate addresses a key issue with candidate gene approaches, which is that examination of single variants in isolation is at odds with our understanding that behavioral outcomes have a polygenic architecture. Now that there are relatively inexpensive methods for genotyping hundreds of thousands of genetic variants across the genome (< 100 USD), researchers can easily calculate polygenic risk scores, which sum across hundreds of thousands of genetic variants in order to capture aggregate genetic risk. These polygenic scores can be carried forward into studies of GxE in which, in theory, the G represents a more global index of genetic risk (Salvatore, Aliev, Bucholz, et al., 2014; Salvatore, Aliev, Edwards, et al., 2014). However, we note that using polygenic risk scores in tests of GxE assumes that most of the genes of interest for that trait are moderated in the same way.
