Multiple sclerosis (MS) is a disabling disease of the central nervous system that mainly affects people in their young age. Pathogenic mechanisms that bring about the development of multiple sclerosis (MS) have yet to be clearly identified, but considerable evidence indicates autoimmunity plays an important role in its etiology. Autoimmune diseases like MS are postulated to arise from complex interactions between individual genetic susceptibility and environmental factors. Previous infection with Epstein-Barr virus, vitamin D insufficiency and smoking are established risk factors for developing MS.
Environmental effect on development of MS is strongly suggested by its geographic distribution. Prevalence rates are higher in regions in higher latitudes and lower near the equator. The effect of latitude is largely through the exposure to sunlight and Vitamin D synthesis in the body. Most epidemiological studies focusing on the impact of sun exposure and vitamin D levels in MS development have focussed on Caucasian populations. Migration studies, have shown changes in the risk of MS in people who migrate between areas that have different environmental risk factors.
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Another environmental factor that can act as environmental triggers inducing or promoting autoimmunity, are microbial infections. Infectious diseases might also accelerate established, but sub-clinical, autoimmune processes. Chicken pox (Varicella zoster virus -VZV) is a neurotrophic virus that remains in the nervous system for decades and has been hypothesised as a possible agent in MS pathogenesis, but results from most epidemiological or serological studies are insufficient to support an association between MS and VZV infection. Recent studies have reported large amounts of VZV DNA inside blood lymphocytes and CSF from MS patients during acute relapses, which disappeared from the CSF in the same patients during phase of remission. These findings support direct participation of VZV in MS etiology, possibly through host virus interaction.
Both active and passive cigarette smoking and MS risk have demonstrated a dose-dependent relationship. Increased risk is associated with cumulative smoking which is reflected by serum levels of nicotine. This risk subsides after a decade of smoking cessation. Case control studies have shown an estimated 40-80% increased risk of developing MS.Smoking prevention and cessation integrated with other treatment strategies might be a reliable and effective way to improve MS outcomes.
The association between breastfeeding and MS has so far been investigated in few studies, which yielded contradictory results. Spencely and Dick found no association between breastfeeding and MS risk,16 whereas in a study comparing patients with MS who were breastfed for 8.4 months with controls who were breastfed for 12.5 months. Pisacane et al. showed an association between prolonged breastfeeding and decreased risk of MS.
The incidence of MS has been increasing rapidly in many countries, including countries of the Arabian Gulf (currently 31-55 per 100000). Recent studies from Saudi Arabia have reported an increased prevalence, however all the studies are hospital based and do not account for underdiagnosed ing that the inconsiderisease.
Considering that the increase in prevalence of MS has occurred over a short period of time it is likely that environmental factors play a more important than genetic factors. Unlike genetic risk factors, many environmental and lifestyle factors are modifiable and most regions around the globe, especially the gulf countries have exhibited remarkable socio-economic and lifestyle changes in past few decades.
With a reported increase in the incidence globally as well as in the middle eastern region, there is an urgent need to understand the role of modifiable factors traditionally implicated in the causation of MS. Information on these factors which could have a role in disease-causation as well as protection could be incorporated into patient care and into preventive programmes, particularly for individuals with a positive family history of MS and therefore increased risk of developing the disease. Observational and prospective studies in the region are of fundamental importance to confirm or rule out this association.
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