This is the first study aiming to shed light on effect sizes that can be expected on the level of genes. Although small, these effects are substantially larger than those of single variants, as have traditionally been investigated in candidate‐gene research. Also, given that behavior arises as a result of a complex interplay between environment and a large number of genes with small effects, the effect sizes of CADM2 that we find could actually be considered substantial. Looking at the level of genes rather than SNPs is biologically more meaningful and could provide clues on underlying biological mechanisms, which in turn will contribute to a better understanding of transgenerational transmission of risky behaviors and provide clues for designing treatment and prevention programs.
