Overgrowth of the brain, also known as megalencephaly, in Nfix-deficient mice is driven by prolonged neural stem cell self-renewal and is potentially the underlying cause of macrocephaly in MALNS (Oishi et al., 2019); but is this conserved for other OGID syndromes, such as SS and TBRS? The gene discussed is NFIX; the disease is megalencephaly.