Causes
The aetiology of this disease is uncertain. There are several related factors that are thought to cause the condition. These include – genetics, the immune system, environmental factors and previous infection.
Genetics:
32 specific genetic mutations have been identified that are more common in sufferers of Crohn’s disease than in the general population. Crohn’s disease also appears to run in families. You will have a 5-10% chance of getting Crohn’s disease if you have a close relative (father, mother, brother or sister) that has it. With identical twins this risk is increased to a 37% chance of contracting the condition. It is also more frequent in certain ethnic groups which would suggest genetics play a significant role in causing it.
The immune system:
In sufferers of Crohn’s disease, a higher level of TNF (tumour necrosis factor) has been found. The TNF will kill all bacteria, including ones that are important for digesting food. Inflammation is mainly caused by antibodies of TNF. The immune system must be disrupted in some way to cause the higher level of TNF to be released.
Environmental factors:
There is a much higher rate of Crohn’s disease in more developed countries compared to less developed ones. There has also been a significant increase in the abundance of the disease since the 1950s. These statistics indicate that environmental factors from Western lifestyles and since the 1950s could be significant contributing factors to the disease. There are some theories of what these factors could be including the hygiene hypothesis. This suggests that because the environment children grow up in doesn’t contain many germs, their immune system doesn’t develop as well. Another theory is the cold-chain hypothesis. This suggests that the increased use of refrigerators since the 1950s could be linked to the increase rate of the disease. This is because certain bacteria (psychotrophic) can survive in these cold conditions. This means there will be an increased risk of exposure through eating chilled food which could cause the immune response leading to this condition. However, there is no significant evidence for either theory.
Previous infection:
A previous infection is thought to be a possible cause of the abnormal immune response that leads to Crohn’s disease in susceptible individuals. MAP (mycobacterium avium subspecies paratuberculosis) is a bacterium which causes a similar disease (Johne’s disease) in cows, sheep and goats. It is thought to be a possible source of infection and Crohn’s disease sufferers are 7 times more likely to have it in their bloodstream than an unaffected individual. It is thought to be contracted by drinking milk from an affected animal. However, it is not known what role MAP has in the condition.
Smoking:
Smoking is a huge risk factor for Crohn’s disease and you are twice as likely to develop the condition if you smoke. It will also increase the severity and frequency of flare-ups of the disease if you already have it.
Genetics image courtesy of Wikipedia under creative commons license
Fridge image courtesy of Wikipedia under creative commons license
Cow image courtesy of Flickr under creative commons license -https://www.flickr.com/photos/pikaluk/ / CC BY-NC-ND 2.0