Reinforcing the likely maladaptive function of altered levels of FOXG1, deletions and missense mutations in this gene have been associated with an atypical Rett Syndrome and small brain size (Ariani et al., 2008; Bahi-Buisson et al., 2010; Mencarelli et al., 2010). This is interesting, as it suggests that deviations in FOXG1 levels during brain development, in excess and defects, cause opposite modulation in brain growth but a similarly disabling outcome, characterized by intellectual disability and ASD-like symptoms.
