First, haploinsufficiency of the Foxg1 gene due to a partial replacement of Foxg1 coding sequences with the cre gene (Hébert and McConnell, 2000) is associated with impaired development of the telencephalon and microcephaly in heterozygous Foxg1Cre/+ transgenic mice similar to the phenotype of heterozygous Foxg1−/+ null mice (Shen et al., 2018; Frullanti et al., 2016; Eagleson et al., 2007; Kawaguchi et al., 2016). This evidence concerns the gene FOXG1 and microcephaly.