1. Pediatric Neurology Unit, University of Rome "Tor Vergata" Rome, Italy
2. Pediatric Neurology Unit, University of Rome "Tor Vergata" Rome, Italy,
3. Laboratory of Epidemiology and Biostatistics, Istituto Superiore di Sanità Rome, Italy
4. Istituto Scientifico E. Medea, Bosisio Parini Conegliano, Italy
5. Department of Epidemiology, The Johns Hopkins School of Hygiene and Public Health Baltimore, MD