Sufficient evidence of neurodevelopmental deficits stemming from FOXG1 haploinsufficiency or duplication in humans has led to the recognition of “FOXG1-related disorders” as a distinct clinical classification variously involving microcephaly, mental impairment, autism spectrum disorders, and a congenital variant of Rett (RTT) syndrome (Ariani et al., 2008; Florian et al., 2012; Mitter et al., 2018; Hou et al., 2020). The gene discussed is FOXG1; the disease is microcephaly.