Report of the MMR Expert Group
3 Crohn's Disease
This chapter describes:
Inflammatory Bowel Disease (IBD) (paragraphs 3.3 to 3.6);
how common IBD is, based on current evidence (paragraphs 3.7 to 3.9); and
what we know, at present, about the causes of IBD (paragraphs 3.10 to 3.16).
3.1 Earlier chapters have touched upon the way in which inflammatory bowel disease (IBD) and intestinal abnormalities have been considered in the context of people with ASD.
3.2 This chapter focuses on Crohn's disease and IBD more generally, taking account of the issues raised by the Health and Community Care Committee, and recognising that it is a serious and debilitating condition in its own right.
3.3 Crohn's disease is a form of inflammatory bowel disease. It is a chronic condition, in which the intestines become swollen, inflamed and ulcerated. Symptoms can include pain in the abdomen, loss of weight, diarrhoea, anaemia, tiredness and lack of energy. Some patients also have swollen joints, inflamed eyes or skin rashes.
3.4 Most patients experience intermittent and unpredictable flare-ups of symptoms with periods of better health in-between. Treatment with drugs or surgery can control or reduce most of the symptoms, but many people find that their general well-being and daily activities are affected to some extent, even when the condition is not active. There is no cure for the condition at present.
3.5 There is another form of inflammatory bowel disease called ulcerative colitis which has some similar symptoms, but which affects only the large bowel.
3.6 Neither Crohn's disease nor ulcerative colitis is thought to be infectious.
Prevalence and Incidence
3.7 It is estimated that within Northern Europe about 0.5% of the population has chronic inflammatory bowel disease 33 and the same figure probably applies to the UK.
3.8 The British Paediatric Surveillance Unit (BPSU) reported the incidence of IBD in the British Isles to be 0.52 per 10,000 per year in young people aged less than 16 years. The highest UK regional incidence was Scotland with a rate of 0.65 per 10,000 per year 34.
3.9 Scotland is fortunate in having data on the incidence and prevalence of childhood IBD extending back more than 30 years. The incidence of Crohn's disease in young people in Scotland rose four-fold between 1968 and 1992 from 0.07 to 0.29 per 10,000 per year 35. The most recent estimate of the prevalence of Crohn's disease in children aged less than 16 years is 1.37 cases per 10,000 population in Scotland 36.
The Causes of Crohn's Disease
3.10 It is not known what causes Crohn's disease. Epidemiological data, notably concordance rates in siblings and in twin pairs, have emphasised the importance of both environmental and genetic factors in disease pathogenesis. It has been known for a long time that some families are more likely to suffer from inflammatory bowel disease than others, and recent research has identified particular genes that are found more often in people who have Crohn's disease 37. NOD-2/CARD15 has been identified as an "IBD1 gene" by independent groups in Chicago 38 and Paris 39, and these data have been confirmed in German and British adult populations 40.
3.11 Which precise environmental factors trigger the onset of Crohn's disease are not known. At different times, research has focused on, for example, viruses, deficiencies in the body's immune system, hereditary factors, mycobacteria in water or milk, diet (including breast-feeding in infancy) and lifestyle (including smoking). No single factor has yet been identified as the most likely agent. Stress, which was sometimes thought to be a primary cause in the 1940s and 1950s, is now accepted to be a factor, which may at times make symptoms worse, but does not cause the illness.
3.12 The measles virus is one of the possible environmental triggers suggested as causing Crohn's disease, based on laboratory and epidemiological studies. The Inflammatory Bowel Disease Study Group at the Royal Free Hospital, London, claimed to identify virus particles in the parts of the bowel damaged by Crohn's disease, which
it believed to be evidence of measles infection. It is known that the measles virus can persist within the body long after a measles infection, as occurs, for example, in subacute sclerosing panencephalitis (SSPE), a rare late effect of measles. The Royal Free researchers suggested that the measles virus damages the blood vessels supplying the intestine and that this leads to the damage and symptoms characteristic of Crohn's disease 41. However, other separate groups of researchers have since reported that they cannot find measles virus in tissue affected by Crohn's disease 42. The Royal Free research group has also repeated its original work using more sensitive tests and has been unable to detect measles virus 43.
3.13 Since the publication some years ago of Swedish and UK epidemiological surveys suggesting a link between measles virus, vaccine and Crohn's disease 44, most published research from the UK and elsewhere has reported no evidence of any such link 45.
3.14 The possible connection between MMR vaccine, bowel disease and autism was raised first by the Royal Free Hospital researchers, in a report published in the Lancet46. This article and later publications 47 have been reviewed by a number of expert groups 2. While there may be abnormalities of the bowel in some children with ASD, it is not proven that they are either a feature of, or involved in, the pathogenesis of ASD. Moreover they are not the same as those found in childhood Crohn's disease.
3.15 It is, of course, important that all this research is carried forward in an effort to learn more and more about Crohn's disease. The Expert Group welcomes plans to undertake more epidemiological research of, and investigation of, environmental risk factors for early onset of IBD in Scotland which will:
Help to define the natural history of IBD in childhood.
Obtain data on early onset incidence for 10% of the UK population.
Undertake genetic and environmental studies in a large and clearly defined population.
3.16 The Expert Group recommends that The Scottish Executive and the Medical Research Council should work together to drive forward and fund, as appropriate, that research into inflammatory bowel disease in children.
Chapter 3 - Summary of Key Points
Crohn's disease is a form of inflammatory bowel disease. It is a chronic condition, for which there is no cure at present.
The most recent estimate of the prevalence of Crohn's disease in children aged less than 16 years is 1.37 cases per 10,000 population in Scotland.
We do not know what causes Crohn's disease. Epidemiological data have emphasised the importance of both environmental and genetic factors. Which precise environmental factors trigger the onset of Crohn's disease are not known. Some researchers have suggested a possible connection between MMR vaccine, bowel disease and autism. All relevant research has been reviewed by a number of expert groups, and, while there may be abnormalities of the bowel in some children with ASD, the scientific evidence does not support the conclusion that they are either a feature of, or involved in, the pathogenesis of ASD.
The Expert Group has recommended more research into inflammatory bowel disease in children.