MTF1 and Zinc deficiency: Given that several candidate genes that are associated with ASD, such as metallothioneins (MTs), zinc transporter 5 (ZnT5; SLC30A5), Zrt- and Irt- like Protein 5 (ZIP5; SLC39A5), metal responsive transcription factor-1 (MTF1) (Serajee et al., 2004; Levy et al., 2011; O'Roak et al., 2011; Sanders et al., 2012) are involved in zinc homeostasis, one might speculate that prenatal zinc deficiency in humans might act as potent trigger in individuals with specific genetic susceptibility due to variants in these ASD candidate genes with otherwise low penetrance.