Interestingly, these mechanisms may be affected in congenital microcephaly linked to environmental intrauterine insults, such as viral infections (Cheeran et al., 2009), alcohol, or other extrinsic cues, exemplified by the finding that Mcph1, the mouse ortholog of human MCPH1, was shown to be down-regulated in a mouse model of microcephaly induced by early embryonic exposure to a VIP (vasoactive intestinal peptide) antagonist (Passemard et al., 2011). This evidence concerns the gene VIP and viral infectious disease.