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EPIDEMIOLOGY


INTRODUCTION This section of the report covers the following epidemiological aspects:


• Risk factors (also known as etiology): the causes of IBD and/or the factors that are linked to the occurrence of IBD;


• Prevalence: the number of people who have IBD at a given point in time; • Incidence: the number of new cases of IBD that can be expected each year; • Mortality: the occurrence of death in people with IBD.


ETIOLOGY


The causes of CD and UC have not been determined. There is growing evidence suggesting that there is a combination of genetic and environmental factors that inappropriately activate the gastrointestinal immune system. Research looking into internal and external factors contributing to IBD includes the search for specific bacterial triggers, as well as other environmental triggers such as diet, antibiotic use and lifestyle. The possibility of more than one environmental or infectious trigger that leads to a similar set of symptoms confounds the research agenda to find both a cause and a cure for IBD.


While the specific causes of IBD are not known, there are some patterns of disease occurrence that have been observed. The strongest of these is the geographical pattern. IBD is emerging as a global disease, but with distinctly different patterns among nations. For reasons that are not clearly understood, IBD is largely a disease of the developed world, particularly Europe and North America. IBD seems low in developing countries, but as these societies become more industrialized, UC emerges. Subsequently, CD rates begin to climb, ultimately predominating in developed nations.5 disease of the new country.6


When people migrate, they take on the frequency of In support of the role of environmental factors, children of migrants


from developing countries are much more likely to develop IBD than their parents. In Canada, for example, South Asian children in Vancouver are three times more likely to develop IBD than non-South Asian children.7


IBD clusters in families, although on most occasions there are no affected relatives. Siblings are most likely to be affected; the risk of IBD in a sibling is 10 to 20 times higher than the general population.8,9


will both have CD, while 10% will both have UC.10,11


The strongest evidence is from twin studies. Up to 50% of identical twins However, the reverse is also true: for at


least 50% of identical twins, only one of the two will have IBD, and the other twin will not have CD.


Researchers have found links to the development of IBD with more than 160 genes and loci. The growing number of identified mutations associated with CD and also UC may help to understand the pathways that lead to disease and identify new targets for treatment. The most important mutation identified thus far is in a gene known as NOD2/CARD 15; it occurs up to three times as frequently in people with CD than in the general population.12,13,14


This single


mutation cannot predict who will get the disease, since it also occurs in people without CD (in other words, many people who will never get CD also carry this mutation). Mutations like this one may eventually serve as a marker for type and/or severity of disease.15,16 number of identified mutations associated with CD and also UC may help to understand the


THE IMPACT OF INFLAMMATORY BOWEL DISEASE IN CANADA 27


The growing


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