1. Department of Neurological Sciences, ‘La Sapienza’ University, Rome, Italy,
2. Fondazione Italiana Sclerosi Multipla, Rome, Italy
3. Department of Neurological Sciences, ‘La Sapienza’ University, Rome, Italy
4. Department of Neurology, Ospedale San Camillo-Forlanini, Rome, Italy
5. Laboratory of Epidemiology and Biostatistics, Istituto Superiore di Sanità, Rome, Italy