Tolerability of the Immersive Virtual Reality System Grail in Subjects Affected by Rett Syndrome

The main goal of this study is to investigate the tolerability to the use of the GRAIL system in subjects affected by Rett syndrome, particularly referred to: 1. Grail environment (training in dark conditions, interaction with wide and surrounding screen, positioning over the treadmill); 2. time to prepare a set of body marker in order to execute a gait analysis; 3. walking activity over treadmill, with immersive virtual reality; 4. proprioceptive stimulatione provided by the GRAIL platform; 5. cognitive-attentive span time to the activity proposed. The secondary goal is to understand if a training that avail of treadmill and virtual reality would be useful in the future in improving gait characteristics in subjects affected by Rett syndrome