“Leaky gut autism theory doubted”, was the headline from BBC News on March 17 2008. The Daily Telegraph and the Daily Mail also reported that researchers have found no evidence to support the ‘leaky gut theory’. They say that this theory proposes that vaccines such as MMR damage the intestine causing digestive problems, leading to the production of peptides “which can damage the brain and possibly cause autism”.

This well conducted study used reliable analysis techniques to compare autistic children across a broad range of intelligences to age-matched control children. Despite the newspaper headlines and coverage, the study did not look at the effects of the MMR jab and autism. Instead, it tested and compared the urine of autistic boys with the urine of boys without autism. The researchers conclude that there were no differences between the levels of peptides in the groups and say they have effectively disproved the ‘leaky gut theory’. However, further research is needed to establish whether a casein and gluten-free diet has other effects on autism.

The researchers call for more studies into special diet as a treatment for autism, but they do not suggest that their research has any implication for the discredited MMR vaccine/autism theory.

Where did the story come from?

Dr Hilary Cass from the Great Ormond Street Hospital for Children and colleagues from around England and Scotland carried out the research. The authors acknowledge the support of the research and development fund of the Royal Hospital for Sick Children in Edinburgh and the Chief Scientist Office in Scotland. Competing interests were declared. The study was published in Archives of Disease in Childhood, a peer-reviewed medical journal.

What kind of scientific study was this?

This was a case control study that compared 65 boys with autism, aged between five and 11 years, with 158 control boys of a similar age.

The researchers say that, for a number of years, it has been thought that the urine of children with autism contains opioid peptides that originate from outside the body. Opioid peptides are chemical compounds that are so called because they resemble morphine. They can be produced by the body and through the digestion of foods such as grain and milk. Grains such as wheat, rye, barley and oats contain the protein gluten, that produces opioid peptides in the gut, while milk produces another variety, casein.

One theory for the development of autism is the ‘leaky gut theory’: the idea that children with autism become sensitive to gluten. The gluten is thought to inflame the small bowel. The resulting damage allows opioid peptides from food to be absorbed into the blood and then enter the urine. Before the opioid peptides in the blood are excreted they are assumed to cross into the brain and result in the symptoms of autism. Previous research has proposed that excluding casein and gluten (milk and grains) from the diet might help children with autism by reducing the amount of circulating opioid peptides.

The theory proposes that opioid peptides found in urine reflect a disturbance in the integrity of the gut epithelium (i.e. a leaky gut). Proponents of the theory hope that the peptides can act as a diagnostic marker for autism and predict that a diet excluding gluten and casein could help to treat children with autistic symptoms.

This study aimed to determine the occurrence of the peptides in the urine of children who have autism and those who do not. The researchers recruited 65 boys from two hospitals specialising in autistic spectrum disorders in London. For the control group, 202 non-autistic boys of similar age were recruited from mainstream infant and primary schools in the same area. A questionnaire was given to the parents of the controls to ‘screen out’ children with possible neurological or psychiatric difficulties. Forty of the controls were excluded from the study as their parents did not complete the questionnaire, or the boys’ results were abnormal or borderline.

Urine samples were collected from all the children and analysed using equipment that separates the chemical in a liquid (HPLC). Other equipment was used to identify small and fragile biological molecules, such as the opioid peptides (MALDI-TOF MS).

What were the results of the study?

The researchers say that their study finds no evidence of opioid peptides in the urine of boys with autism or similar disorders.

After adjusting for the amount of creatinine in the urine, which is a measure of kidney function, the researchers found no significant differences in the urinary profiles (shown by HPLC) between groups of boys with or without autism. In those cases where HPLC showed peaks in the locations at which opioid peptides might be expected to be found, further testing by mass spectrometry (MALDI-TOF) showed that these peaks did not represent opioid peptides.

What interpretations did the researchers draw from these results?

The researchers say that “given the lack of evidence for any opioid peptiduria in children with autism it can neither serve as a biomedical marker for autism, nor be employed to predict or monitor response to a casein and gluten exclusion diet”.

The researchers say that these findings effectively disprove the ‘leaky gut theory’, which predicts that these proteins should be found in the urine of autistic children. They suggest that healthcare professionals and parents should stop testing children with autism for urinary opioid peptides, and note that commercial laboratories around the world  still widely advertise these tests on the internet.

What does the NHS Knowledge Service make of this study?

This study has a number of strengths. The researchers used accepted and applied definitions of autism and selected children across a broad range of intelligence. The urine testing appears to have been conducted reliably and the researchers further analysed the peptide peaks found by chromatography (HPLC) with advanced mass spectroscopy techniques (MALDI-TOF).  They acknowledge some limitations, however, including:

The autistic children were selected from tertiary or specialist centres. This may mean that they had more severe autism than that commonly found in the community.

It was not possible to match the autistic children with low IQ to control children with the same level of IQ. Strictly speaking, this means that the groups were not balanced at the start of the study. However, as no significant differences were found in the peptide levels between any of the groups that were examined, it is unlikely that a link would have been found between peptide levels and IQ either.

The researchers say that there is no evidence that opioid peptides can leak through the gut and cause autism in children. However, further research is needed to establish whether a casein and gluten-free diet has other effects on autism.

The researchers do not comment on any implications of their study with regard to the MMR vaccine.  Immunisation is topical and attracts the reader’s attention, but well-designed research into other theories of how autism is caused is needed.