there are many genes of small effect, each gene is a tiny window that offers a peek at the brain’s functioning. Moreover, looking through many of these windows simultaneously could lead to a systems approach to the brain because each of the many genes was identified on the basis of its association with a behavioural disorder. Similarly, sets of genes associated with behavioural disorders will also be useful in top-down analyses that begin with behaviour and investigate multivariate, developmental and genotype-environment interface issues, and translate these findings into gene-based diagnosis and personalised treatment as well as prediction and prevention of disorders (Harlaar, Butcher, Meaburn, Craig, & Plomin, 2005).
