The breathing abnormalities are not typical of Rett syndrome, however the breathing patterns are an essential element of the diagnosis, for example, the evaluation of the ANS allows the distinction between non-epileptic paroxysm and epilepsy, contributes to the diagnosis in MECP2 negative forms, allows to design a personalized therapy [17], and eventually, taking into account all the limitations, a better prognosis. This evidence concerns the gene MECP2 and Rett syndrome.