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What does cause autism?
We do not know what causes autism. It's a question that has frustrated parents and researchers for decades. What has become clear is that there is an important genetic role. There is a higher rate of autism amongst relatives of those with the condition and a strong genetic link has been shown by studies of identical twins. Researchers around the world are currently trying to track down the genes involved.
However, genetic causes cannot be the only factor. Environmental factors may also play a role, but what these are, and to what extent they can have an effect is a matter of huge debate. Many environmental factors have been suggested but so far none has been proven as a major cause of autism.
We do know that in a very small proportion of cases of autism a specific medical condition is involved (such as in the genetic disorders phenylketonuria and fragile X). This also raises the possibility that there may be several different types of autism, with a number of different causes. Autism is not a single condition, but a spectrum of disorders defined by similar behaviours - so there are likely to be different underlying causes at work.
A major study is now going on tracking 100,000 children in Norway. The Autism Birth Cohort, led by researchers at Columbia University, New York, is the largest study of its kind in history. It will follow children and their parents for five years, beginning during the mother's pregnancy. It is hoped this will help to identify these possible causative factors.
Has there really been a huge increase in the number of autistic people?
This is an area of huge debate. It is unquestionable that the number of people diagnosed with autism has increased significantly in the past few decades.
However, we now recognise a much wider range of disorders under the "autistic spectrum" banner. For instance people with Asperger's syndrome, who can have high IQs and can often integrate well into society, would not have been diagnosed on the autistic spectrum until relatively recently.
As well as changes in official diagnostic criteria, the rising awareness of autism has undoubtedly played a role in the increasing numbers. There is no objective test for autism and therefore the numbers diagnosed depends on the skill and experience of the medical community which have improved significantly.
Yet there is no proof that these factors account for all of the increase. Equally there is no proof that any environmental factor has caused a real increase. All we can say for sure is that increased diagnosis accounts for at least part of the increase.
If there have always been more autistic people then where are they?
As described above, many of the people on the autistic spectrum who were not diagnosed will have Asperger's Syndrome. Many of these people will be living full lives in the community and may not consider themselves to be autistic.
People with more severe forms of autism may have been diagnosed with other conditions. A study by Jick and Kaye found that as more people have been diagnosed with autism, there has been a similar decrease in other less specific diagnoses (such as 'behaviour' and 'developmental' disorders).
Is there a link between autism and bowel disease?
There is growing recognition that many autistic people suffer from bowel symptoms that cause very real pain and distress. What is certainly not clear is whether it is the autism that can cause bowel problems or the bowel problems that can help cause autism.
It is known that people with neurological problems, like autism, are particularly likely to experience these gut symptoms. This may be because the brain and the gut are closely connected through the nervous system. Autism involves the incorrect functioning of parts of the brain, and therefore it would not be surprising if this led in some cases to the bowel not functioning correctly.
In addition, the bowel problems may be exacerbated by the autistic behaviour affecting the diet of the person. People with autism can sometimes develop very strong food preferences - such as only eating one type of food, or only food of a certain colour - which can itself produce bowel problems.
It is also inevitable that some people with autism will suffer from bowel diseases such as Crohn's and ulcerative colitis, which can sometimes be very serious. This does not mean that these conditions are linked with autism. It is just that some people will be unfortunate enough to be affected by both, because bowel conditions are found across the population.
The question of whether there are also unusual biological abnormalities in the bowels of some autistic people is one that is currently being investigated. Some researchers claim to have seen unusual immune cell patterns or distinctive microscopic features in the bowel tissue of some autistic patients. Recent work has also suggested that there may be differences in the immune systems of people with autism, and so it might be possible that this could affect the gut. It is not known yet if these differences will be confirmed, and if so, whether they are specific to autism or also found in other conditions.
If a link between such bowel disease and autism were proven it would not in itself support the existence of a link between MMR and autism. If the bowel disease was indeed new and had not existed before the introduction of MMR this might point towards a link. There is no convincing evidence that this is the case. Indeed, researchers have reported finding such bowel problems in autistic children who have never had MMR.
Is work still going on to investigate the connection between MMR and Autism?
The vast majority of scientists consider that the weight of evidence shows there to be no link between the MMR and autism. However, there are still several major studies that are in progress to see whether they can reproduce or refute the clinical work of Dr Andrew Wakefield. Three separate studies in the USA are looking for the measles virus in gut tissue samples from autistic children.
As described above, many scientists are investigating the nature of the bowel disease that some autistic children suffer from. It is not clear whether this will shed any light on the question of whether MMR is linked to autism.
Dr Wakefield continues his research looking in particular at children who have received multiple doses of MMR.
Further reading:
"MMR and Autism: What parents need to know" by Michael Fitzpatrick
Published by Routledge 2004
"MMR: Science and Fiction - Exploring a Vaccine Crisis" by Richard Horton
Published Granta Books 2004, ISBN: 1862077649
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