FOXG1 and microcephaly: The homozygous loss of Foxg1 in mouse leads to a severe reduction in telencephalic structures (5), and the loss of one copy of FOXG1 in human leads to postnatal microcephaly, severe developmental delay, and structural brain deficits such as cerebral atrophy, gyral simplification, hypomyelination, and a thin or absent corpus callosum (6).