The onset of multiple sclerosis (MS) occurs in childhood in about 5% of all patients with MS. The disease in adults has a complex genetic and environmental inheritability. One of the main risk factors, also confirmed in pediatric MS, is HLA DRB1*1501. In addition to genetic factors, a large part of disease susceptibility in adults is conferred by environmental risk factors such as low vitamin D status, exposure to cigarette smoking, and remote Epstein-Barr virus (EBV) infection. In children, both exposure to cigarette smoking and prior EBV infection have been reported consistently as risk factors for MS. The role of vitamin D remains to be confirmed in this age category. Finally, although very likely critical in disease processes, few gene-environment interactions and epigenetic changes have been reported for adult and pediatric MS susceptibility. Of interest, some of the risk factors for MS have also been associated with disease course modification, such as low 25(OH) vitamin D serum levels in pediatric and adult MS. Age is also a clear disease modifier of clinical, CSF, and MRI phenotype in children with the disease. Finally, although much has yet to be unraveled regarding molecular processes at play in MS, there is a larger gap in our knowledge of genetic and environmental risk factors for pediatric neuromyelitis optica spectrum disorders and acute disseminated encephalomyelitis and only collaborative studies will answer those questions. Among pediatric acquired demyelinating disorders of the CNS, multiple sclerosis (MS), including clinically isolated syndromes (CIS), acute disseminated encephalomyelitis, and neuromyelitis optica (NMO) spectrum disorders are the most common. Due to its chronicity and proportionally higher incidence, substantial efforts have focused on understanding factors contributing to MS, although the study of risk factors for NMO is also accelerating.
1Despite the fact that several genetic and environmental risk factors have been consistently reported for adult MS, 2 underlying molecular processes at play remain largely unknown. The onset of MS in children, although representing only approximately 5% of all MS onsets, leads us to question whether the load of genetic factors and environmental exposures contributing to disease onset may in fact be higher than in adults who develop the disease. As such environmental risk factors should be easier to identify in younger patients and if disease processes at play overlap in all age groups, this information might be extended to adult-onset MS. It is unknown why disease onset is relatively rare in children vs adults. This could be in part due to developmental changes in the CNS or immune systems.Exposures to environmental risk factors for adult MS are believed to occur for the most part before age 15.2 As such, studying risk factors in pediatric MS during the putative window of disease susceptibility may considerably shorten the time between exposure action and time of