**3. Etiology and risk factors**

Pediatric MS has a complex etiology related to both genetic and environmental factors. Vitamin D deficiency has been implicated as a risk factor for MS in children, as it is in adults. Mowry et al. have demonstrated an association between relapse rate and vitamin D level in pediatric MS patients [6]. Smoking has been considered as a risk factor in adults, whereas passive smoke exposure has been recognized as a risk factor in children [7]. One of the most studied envi‐ ronmental risk factors is viral exposure and studies have found that viral exposure in child‐ hood may predispose some individuals to the development of MS. Epstein-Barr seropositivity and serum anti-EBV antibody titers tend to be higher in MS patients than they are in normal individuals. The relationship between the Epstein-Barr virus and MS has also been shown in pediatric MS [8]. Another risk factor is obesity. Childhood and adolescent obesity has been suggested as a risk factor for the development of MS in both adults and children [9]. Genetic susceptibility is also a risk factor for MS. HLA-DRB1 locus has been associated with multiple sclerosis in children. Twin studies have demonstrated a concordance rate of 27% in monozy‐ gotic twins. The incidence for first-degree relatives of patients with MS is 2–5%, whereas the incidence for the general population is under 0.1% [10].
