Mutations in the X-linked gene encoding MECP2 (methyl-CpG-binding protein 2) account for 90–95% of the case of classic Rett syndrome (RTT) [3,4] while mutations in the X-linked gene encoding cyclin-dependent kinase-like 5 (CDKL5) account from some cases of atypical RTT that manifest with early refractory epilepsy [5]. This evidence concerns the gene CDKL5 and atypical Rett syndrome.