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Geographic Clustering and Autoimmune Disease

There are many diseases and conditions that have been putatively linked to living or working in certain locations, which is known as geographic clustering, or geo-clustering. Today we will examine a few important facets of this phenomenon, in general as well as for specific disorders

What is geographic clustering in general?

As stated above, geographic clustering can be broadly defined as the appearance of clusters (groups) of people suffering from certain diseases, where the numbers of patients are statistically higher than is expected normally in other regions, whether nationwide or worldwide. Probably the most well known examples are so-called “cancer clusters”, where doctors have reported higher than average rates of certain types of cancer as a function of where these people live or work (i.e., spending long periods in that place). Lyme disease is so named because of an initial geographic clustering near Lyme, CT. But geographic clustering has been identified in several autoimmune disorders as well.

Unfortunately, while a host of potential causative factors, such as radiation, electromagnetic waves (people living near big electrical towers or plants), genetic mutations, local diet and environmental toxins are all suspected contributors to geo-clustering, it is often hard to pinpoint what, if anything, is the dominant or definite cause.

This is because it is difficult to isolate all of the possible contributing factors that may be influencing onset of disease. Still, statistically speaking, when one area shows spikes that can’t be accounted for otherwise, it is important to make an effort to discern whether this phenomenon is a result of real environmental dangers or familial traits, or simply a statistical anomaly for which there is no apparent explanation. Of course if this can somehow be achieved and it is determined to be related to exposure to certain toxins, then an effort should be made to avoid the possible insulting factors by changing locations and either moving or switching jobs. Obviously this is often times much easier said than done, as many people can’t simply pick up and move readily, which may pose additional problems in the future.

Is there statistical geographic clustering for the following autoimmune conditions?

Multiple Sclerosis: According to the National MS Society and many other reputable sources, yes, there is definitely a difference in geographic distribution of the disease according to region. The highest prevalence of disease is found at northern latitudes, further away from the equator, as well as in those with Northern European ancestry. While no specific cause has been proved, decreased Vitamin D as a result of less sunlight has been implicated as a possible contributor.

Celiac Disease: Uncertain. Those of Northern European ancestry do have a higher incidence of disease, and one article in the Journal of Pediatric Gastroenterology and Nutrition cited several Middle Eastern and African populations as areas of geographic clustering, but noted that studies are ongoing. Other than these examples, no other credible sources presented similar evidence or assertions, though location is still suspected as a contributor. To be sure, there are definite dietary clusters, which is the reason behind avoiding all gluten-containing products.

Inflammatory Bowel Disease/Crohn’s Disease: According to the Mayo Clinic and Johns Hopkins, yes, there do seem to be geographic clustering in certain areas, most of which have been recently identified. These include Israel, Alberta, Canada, Northern Europe, Australia, South Africa, temperate North America, and urban areas, but evidence is lacking beyond this finding that would provide further information and confirmation of this suspicion.

Psoriasis: A dermatologist colleague of mine stated that he knows of no geographic clustering identified thus far as a factor in developing psoriasis. However, he did say that there is likely some effect on disease based on location, in that sunnier climates may have slightly less sufferers because of the immunosuppressive effects of sunlight, which are well known.

Hashimoto’s Thyroiditis: After searching online, nothing was found regarding identified regions of higher incidence or prevalence, though it is still possible that such geographic clustering does exist and hasn’t been recognized. Since radiation and high iodine consumption are known to contribute to this condition, the potential for geo-clustering in areas affected by these factors (such as Hiroshima and Nagasaki) is quite real, though they would be driven by non-indigenous causes and therefore probably not considered true geo-clustering.

How can geographic clustering affect prevention, onset, diagnosis and treatment of disease?

The answer to this question will partly depend on the conditions and locations being considered, but preventive measures might certainly include removing oneself from an area of suspected clusters, or where known causes of disease are present. It’s difficult to say what the exact impact may be on disease onset, but it is possible that disorders may begin earlier or in groupings, according to the levels of suspected contributors/toxins in the area.

As for diagnosis, if suspected causes are known, doctors in the area may be more prone to administer regular screenings at a higher rate than normal, and specific or special tests that would not normally be part of a lab battery may be standard in these locations. Treatment options will not usually change from those used in the general population, unless the patient and/or physician can identify and remove the insulting factors.

Questions for your doctor:

  • Is there evidence of geographic clustering in my home or work area? If so, for what conditions?
  • For my condition(s), what are the major suspected contributors?
  • Are there studies that I can read (i.e., that are lay person friendly)?
  • Do I need to do or take anything to avoid or prevent onset of disease?
  • How do you/doctors determine whether a disorder is related to location? (You’re not likely to get a very good answer to this one, but it’s still an important question to ask.)

 

About the Author
Dr. Rothbard is a professional medical writer and consultant based in New York City, specializing in medical education articles targeted at a variety of audiences, from children through clinicians.  After leaving medicine, he worked as a biology and medical science educator for several years, before deciding to pursue writing fulltime.  He may be reached at [email protected].

 

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