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Investigating etiology through space/time epidemiology |
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Multiple Sclerosis Geographics |
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What is Multiple Sclerosis? |
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Introduction Multiple sclerosis (MS) is the most common primary neurological disorder of young adults, according to Warren et. al.. Researcher Stephen Waxman calls it “the archetypical inflammatory demyelinating disease of the central nervous system.” Demyelination is the degradation of the fatty myelin sheath surrounding axons. This myelin sheath is essential for the transmission of axon potentials, the mechanism by which neurons communicate.
Etiological Theories MS was first diagnosed some 600 years ago, although its cause remains unknown. MS is generally labeled as an autoimmune disease. According to this theory, demyelination is a result of immune system malfunction, by which the immune system agents attack the myelin sheath surrounding axons in the central nervous system (CNS).
Other researchers believe MS is the result of a stealth pathogen. This group can, in turn, be divided into two cohorts. The first believes that the pathogen at work is a virus. In particular, Ebstein-Barr Virus is the subject of much research [Haahr]. The second cohort, growing in numbers, believes that the pathogen is a bacterium. Many believe this bacterium is similar to that involved in Lyme disease. In fact, late stage Lyme disease resembles an autoimmune attack on the myelin sheath, or the general description of MS [Filley]. Sclerotic plaques are seen in both cases.
Prevalence MS affects approximately 400,000 Americans and 2.5 million people worldwide. It is also between two and three times as common among women as among men [National MS Society].
MS is widely believed to increase with latitude. Distribution maps of MS support this theory, as well as show higher prevalence around large bodies of water, including the Atlantic and Pacific Oceans and the Great Lakes [Blewett].
Evidence for and Identification of Possible Environmental Agents Epidemiological evidence strongly suggests that an environmental agent is at work in MS. Quoting the National Institute of Neurological Disorders and Stroke: “MS is five times more prevalent in temperate climates-such as those found in the northern United States, Canada, and Europe-than in tropical regions. Furthermore, the age of 15 seems to be significant in terms of risk for developing the disease: some studies indicate that a person moving from a high-risk (temperate) to a low-risk (tropical) area before the age of 15 tends to adopt the risk (in this case, low) of the new area and vice versa. Other studies suggest that people moving after age 15 maintain the risk of the area where they grew up. “These findings indicate a strong role for an environmental factor in the cause of MS. It is possible that, at the time of or immediately following puberty, patients acquire an infection with a long latency period. Or, conversely, people in some areas may come in contact with an unknown protective agent during the time before puberty.”
The elusive environmental agent is believed by many researchers to be either a bacterium or a virus. Different ethnic groups have different risks of acquiring MS, suggesting a genetic component of MS. This genetic component may in part be determined by immunity against an unknown environmental agent, be it bacterial or viral.
In light of the growing controversy over the role of environmental agents in MS, spatial statistics is a powerful tool for investigating MS. By identifying where higher incidence of MS is found and where clusters occur, possible environmental agents can be determined. This in turn would provide key insight into therapeutic options. The cause of MS has eluded researchers for some 600 years; using spatial statistical technology only made available in recent decades could help end this search and allow the next phase of MS research to begin: finding a cure.
Further Information for Patients:
· MS clinics in the United States · MS news
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© Blewett 2007 |
