By Dr Ananya Mandal, MD
The exact cause of Crohn’s disease is unknown. There are, however, a combination of factors that are found to be associated with Crohn’s disease.
Some of the factors associated with Crohn’s disease include:-
Crohn’s disease usually runs in families. Around 3 people in 20 of those affected have a parent or a sibling affected with this condition.
Persons with an identical twin with this condition have a 70% risk of getting the condition.
There are at present 32 identified different specific genetic mutations that are seen more commonly among the sufferers of Crohn’s disease.
Some racial and ethnic groups are also more susceptible to this condition than others. For example, people of Jewish heritage have an increased risk of developing Crohn’s disease and those of African American descent have the lowest risk. This also suggests a genetic association.
Dysfunctional immune system
The immune system protects the body from foreign invaders and harmful microbes. There are also millions of friendly bacteria that reside normally in the gastrointestinal tract. These are called commensal organisms and may help in absorption and digestion of food, manufacture of vitamins and several other processes vital for living.
The body’s immunity recognises these friendly bacteria and does not attack them.
In Crohn’s disease the immune system goes into an overdrive attacking all microbes and cells in the intestines.
The immune system particularly produces a special antibody, known as tumour necrosis factor (TNF) to kill all bacteria. These TNF antibodies cause most of the inflammation associated with Crohn’s disease.
Early episodes of infection
It has been seen that in some genetically susceptible individuals some previous or childhood infections lead to conditioning of the immune system and makes it react in an overwhelming manner. This leads to symptoms of Crohn’s disease.
One of the infections that has been named with certainty in some studies includes Mycobacterium avium subspecies paratuberculosis (MAP). MAP is commonly found in cattle including cows, sheep and goats.
Those with Crohn’s disease are seven times more likely to have a previous infection of MAP.
It has been seen that Crohn’s disease more commonly affects the westernized nations like UK and USA rather than poorer African countries. This brings to attention the environmental factors that may be responsible for this condition.
The condition has also been recognized after the Second World War and was rare before that. This also points towards an environmental change that may be responsible for increased prevalence.
Some scientists suggest that one of the reasons for this rise today, especially in the westernized nations, is that children grow up in increasingly germ-free environments making them less resistant or immune to infections. This is called the hygiene hypothesis.
Another theory is the cold-chain hypothesis. This suggests that the increase in the number of cases of Crohn’s disease might be linked to the increased use of refrigerators. These theories are not proven.
Smoking as such does not appear to cause Crohn’s disease. However, smokers have been found to be twice as likely to develop Crohn’s disease compared with non-smokers and they also have more severe symptoms compared to non-smokers.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)