This is an open-label, single-blinded, observational, prospective, 24 months follow-up, controlled study to assess the efficacy of Gilenya on thalamus pathology and cognitive impairment in 30 relapsing MS patients naïve to Gilenya who fulfilled the inclusion and exclusion criteria used for screening and started Gilenya, on a clinical basis. In addition, 20 HCs will be included as a reference population. Because this is an observational study investigating evolution of thalamic atrophy, iron deposition, cognitive dysfunction and response to herpes viruses in patients treated with Gilenya on a clinical basis the patients are not starting Gilenya as an investigational drug. Therefore, the patients who are already started Gilenya by the treatment decision of their physician will be asked to participate in this observational study.