In humans, either gain- or loss-of-function Foxg1 mutations cause ‘FOXG1 syndrome’, an autism spectrum disorder (Hou et al., 2020; Hettige and Ernst, 2019; Florian et al., 2012) that results in a range of conditions that include microcephaly, seizures and may also increase the propensity for glioblastoma or myelination deficits (Hou et al., 2020). Here, FOXG1 is linked to Down syndrome.