FOXG1 and Rett syndrome: Importantly, FOXG1, a transcription factor critical for telencephalon development and associated with atypical Rett syndrome and small brain size (Ariani et al. 2008; Kortum et al. 2011), was found abnormally up-regulated in ASD patient-specific organoids, and lentiviral-mediated knockdown of FOXG1 was able to rescue the aberrant high production of GABAergic neurons in ASD patient-specific organoids (Mariani et al. 2015).