Accordingly, the overexpression of IGF-1 in rodent brains resulted in brain enlargement, while the deletion of IGF-1 or conditional deletion of IGF1R expression in the brain led to microcephaly and hypomyelination (Beck et al., 1995; Zeger et al., 2007; Kappeler et al., 2008). This evidence concerns the gene IGF1 and microcephaly.