Despite extensive and continuing research the cause of Crohn’s Disease is still unknown. However, there are a number of predisposing factors, which may play a part in the development of the disease:

1. Genetics and Heredity
The occurrence of Crohn's Disease in more than one member of a family is more common than would be expected, thus, there is a hereditary tendency. The risk to family members varies considerably between studies but is generally highest when a brother or sister is affected. Studies on twins have also shown a higher incidence amongst identical compared to non-identical twins.

Extensive work is being carried out in this area in order that genetic counseling may be of benefit. Data from studies already carried out suggests that the majority of any class of relatives will not show signs of the disease.

Further information on Genetics and Crohn’s Disease

2. Infection
There is no evidence that Crohn's Disease is contagious. However, some cases start after episodes of gastroenteritis. Some doctors suspect it is triggered by an unusual immunological response to an organism, which is usually relatively harmless, e.g. measles virus or mycobacteria (a micro-organism resembling the bacillus causing tuberculosis).

Others believe that the disease is possibly started by bacteria in the gut that release toxins (poisons), which attack the wall of the intestine and may cause the damage seen in Crohn's Disease. If toxins were absorbed into the bloodstream, it might explain the symptoms that occur outside the intestine such as arthritis, uveitis and skin lesions.

3. Immunological Factors
The body's own defence mechanism (the immune system), which provides protection against infection, is activated by intsetinal bacteria in Crohn's Disease and may be involved in causing damage to the mucosa. Many drugs used to control Crohn's Disease affect this system. However, it is likely that immunological changes are produced after the disease has started rather than causing it.

4. Dietary Factors
Some patients find that their Crohn's Disease is better if they avoid certain foods such as wheat, yeast or milk. However, many other patients with the disease are able to eat these foods. It is possible that the breakdown of certain foods (perhaps by bacteria) in the large intestine plays a part in Crohn's Disease.

5. Psychological factors
Although not a proven cause, periods of emotional stress have been linked with flare-ups of the disease.

6.Measles, MMR vaccine

The measles virus and MMR vaccine have recently been the subject of intense media coverage reporting a link with the development of Crohn's disease. This has caused much concern and anxiety amongst sufferers of the disease and their families.

On the 23rd of March 1998 the chief medical officer, Sir Liam Donaldson, from the Department of Health, together with a group of experts, met to review all recent works and some, as yet unpublished data on the subject. Some of the issues considered included:

1. A Swedish study showed that 3 out of 4 children born to mothers exposed to the virus in late pregnancy went on to develop Crohn's disease. However, two larger controlled studies from England and Denmark showed no increased risk of Crohn's disease under the same circumstances.

2. A comparison of a cohort of children immunised in 1964 with unimmunised children in 1958 suggested an increased risk of Crohn's disease in the immunised group.

However, a second study, which was more reliable as it used appropriately matched controls, and similar studies in Oxford and Finland showed no increase in Crohn's disease following the introduction of the measles or MMR vaccine

3. Workers at the Royal Free Hospital in London have claimed to demonstrate the presence of the virus in tissues of patients with Crohn's disease. However, an independent group, using identical methods could not reproduce these results. Three groups, including the Royal Free Hospital, using the most sensitive and specific techniques, failed to detect measles virus genetic material in either tissues affected by Crohn's disease, normal bowel tissue, or in peripheral blood lymphocytes of Crohn's sufferers.

If measles viruses were present they would have been detected by these methods. In addition, measles specific antibodies do not appear to be raised in individuals with Crohn's disease.

After careful consideration of the material available, together with the opinions of the experts, the following conclusions were made:

• There is no support of a causal role for persistent measles virus infection in Crohn's disease.

• There is no link between the MMR vaccination and bowel disease

• There is therefore no reason for change in the current MMR vaccination policy and that giving the vaccines separately would leave children and their contacts unnecessarily exposed to preventable infectious diseases along with their often serious consequences.

We regret that we cannot make the decision as to whether you should or should not have your child immunised with the MMR vaccine. This decision has to be yours based on the available evidence and the support of the medical team delivering your care.

Further information and support groups available to help you with your decision include:

NACC, 4 Beaumont House, Sutton Road, St Albans, Herts. AL1 5HH.
Tel: 01727 844296
www.nacc.org.uk

The Department of Health. www.doh.gov.uk