The overall objective of both Phase 1 and Phase 2 of the PD-ADS Study is to define the clinical features, clinical epidemiology and genetic epidemiology, pathobiology, neuroimaging features, and outcome of acquired demyelinating syndromes (ADS) of the central nervous system demyelination in Canadian children. The primary goal is to identify those factors which predict Multiple Sclerosis (MS) risk. The identification of such factors provides invaluable insight into potentially modifiable risks, aids in our understanding of MS pathobiology, and provides unique possibilities to identify children who might benefit from early therapeutic intervention. In Phase 2, we will continue to follow the 302 eligible participants enrolled in Phase 1, and will recruit an additional 100 children with demyelination, as well 100 age- and sex- matched healthy control participants. Our investigations will be expanded to include more complex studies of immune cell regulation and brain imaging, and to bridge the gap between bench science and daily life by studying the impact of demyelination (and MS in particular) on psychosocial, cognitive, physical, and health-related quality of life in children. Phase 2 extends the Network established in Phase 1 and now includes 5 Principal Investigators, 38 site investigators, and many scientific partnerships. An ever-increasing cadre of talented trainees (generally funded separately by MSSC or CIHR) works on projects related to the PD-ADS study.