Our analyses revealed that (1) FOXG1 impaired TGFβ-induced neuronal differentiation in early developmental stages, i.e. E13.5; (2) FOXG1 blocks transcription of Cdkn1a, Tgfβ, Foxo1 and Foxo3; (3) expression of Cdkn1a is activated by FOXO1; (4) neither CDKN1A, FOXO1 or FOXO3 can stimulate neuronal differentiation autonomously; and (5) Kcnh3 is a novel neuronal FOXG1-regulated target gene which might be of clinical relevance in atypical Rett syndrome. This evidence concerns the gene FOXO3 and atypical Rett syndrome.