Genetic or pharmacological perturbation of the 5HT system is associated with autism-like behaviours in humans and in rodents (Bauman et al., 2006; Cook et al., 1997; Kane et al., 2012; Klauck et al., 1997; Nabi et al., 2004; Nakatani et al., 2009; Sutcliffe et al., 2005; Veenstra-VanderWeele et al., 2012). The gene discussed is HTR5A; the disease is autism.