In boys, there was no main effect of MAOA-LPR genotype. Unlike in girls, there was no G×E interactive effect on hyperactivity at age 4 years. Hyperactivity at 7 years was not influenced by the interaction of MAOA-LPR genotype with stressful life events experienced between ages 6 months to 3 ½ years (p = 0.1) (Figure 2, A2 and B2). However, there was a significant G × E interaction for stressful life events experienced during the narrower window of 1 ½ to 2 ½ years such that the low activity MAOA-LPR allele was associated with higher hyperactivity at age 7 years in boys who had been exposed to high stress (β = −0.21; 95% CI: −0.21 to −0.01; p = 0.03) (Figure 2, A1 and B1).
