Recent evidence has provided clear support for several mechanistic hypotheses, including: a direct impact of genetic risk factor interactions on neurodevelopment, as in the case of DISC1–Ndel1/Nde1; neuronal circuitry and behavioral deficits arising from impaired synaptic pruning; and the involvement of immune system components in the primary pathogenesis underlying psychiatric disorders. The gene discussed is NDEL1; the disease is psychiatric disorder.