The prevalence of MS is highest in North America, northern Europe and southern Australia. There is a complex pattern of prevalence within these areas (figure 1). In North America, the highest rate is in southern Canada and in the northern United States. The lowest rate in North America is the Mississippi region and surrounding southeastern states. Studies have indicated that early life residence influences the risk of developing multiple sclerosis. These findings suggest environmental factors for the development of the disease, though nothing has been isolated. Additional evidence suggests genetic factors to be involved. Racial susceptibility studies have found Scandinavian descent populations are at a higher risk compared to people of African descent. There has been a genetic marker found in select populations with MS but the mode of transmission and the influence of additional genes is not understood. The genetic susceptibly of MS is the focus of abundant research. Overall, there appears to be combination of genetic and environmental factors contributing to the disease.
Multiple Sclerosis(MS) is considered to be an immune mediated disease. Typically, when our body’s immune response is triggered, lymphocytes including T cells and B cells will be activated. Depending on the type of defense our body requires; various subsets of cells will be activated. In MS, T cells become activated in a genetically susceptible person by a probable environment factor and migrate to the central nervous system (figures 2 & 3). During this activation, cytokines are released to facilitate activation and to enhance the ability of T-cells to travel into the central nervous system (figure 6). Modifications of cytokines are heavily studied in new therapeutic strategies for MS. There are cells called macrophages and microglia that bind antigens, the target for the immune attack. These macrophages and microglia are called antigen-presenting cells. These cells form a complex with the activated T cells (figure 4). This triggers a cascade of events which ultimate leads to the destruction of the myelin and oligodendrocytes, which are cells that produce myelin (figure 5 & figure 6). There has been a significant amount of research indicating destruction of axons is occurring during this process. Areas of the central nervous system affected are referred to as “lesions” or “plaques” (figure 7). Different pathological patterns of demyelination and axonal loss have been discovered in lesions from brains of patients with MS.