A Gut Feeling about Autism?

Max Bingham and Glenn Gibson

Food Microbial Sciences Unit, School of Food Biosciences, The University of Reading, Whiteknights PO Box 2**, Reading, Berkshire

For many parents, they do not need to be told that often their autistic children have some quite serious bowel troubles.  Reports from parents often tell of symptoms as diverse as profuse diarrhoea, constipation, excess wind and bloated stomachs.  One contributing factor for many of these reports might include a severe imbalance in the gut bacteria, where for some reason, more undesirable and possibly toxic bacteria have replaced the more beneficial and protective bacteria.  The work of Dr William Shaw has helped highlight the possibility of a Candida or yeast overgrowth. More recently the research of Dr Sydney Finegold and company has highlighted the possibility of a clostridia overgrowth in a number of autistic children.  Many other conceivable theories are doing the rounds, but in most cases they remain unproven and untested.  From a parental or carer point of view, it must remain a daunting prospect to consider treatments and advice, when the scientific community cannot agree on approaches and the orthodox medical establishment are reluctant to endorse unproven avenues of relevance.  One emerging area of scientific research into Autism and ASD's is the question of whether something unusual is going on with the bacteria naturally found in all our guts.  At the University of Reading, the Food Microbial Sciences Unit has started to ask exactly that question.  While we are still very much in the dark as to what might be going on with these bacteria in autistic individuals, a number of theories have emerged recently.  To put the record straight, Max Bingham and Glenn Gibson explain all.

Gut Microbiology at Reading

Research at the Food Microbial Sciences Unit utilises expertise in gut microbiology, anaerobic bacteriology and molecular biology to reliably identify species and systems involved in a wide variety of applications.  The Human Gut Microflora is an extremely complex mixed culture comprising mainly of bacteria living in a state of dynamic equilibrium.  It is estimated that as many as 500 different species reside in the colon at any one time.  In the small intestine and stomach much lower numbers can be found.  The colon is regarded as one of the most metabolically active sites in the human body and this is due to the human gut microflora.  Until recently, research on the human gut microflora has been limited by the fact that only about 88% of cells observed under the microscope are cultureable.  A much smaller number are easily cultureable.  More recently, the use of molecular based techniques such as DNA extraction and sequencing has meant research can be extended into areas that were previously not possible.

Using the latest molecular and DNA techniques, the bacterial populations naturally found in the gut can be tracked and then using models of the gut probiotics and prebiotics can be used to alter these populations beneficially.  Recent successes in using this approach at the Food Microbial Sciences Unit have included the development of food product concepts that have been clinically proven to promote beneficial bacteria such as lactobacilli and bifidobacteria and thus possibly offer protection from a whole range of pathogenic infections and diseases.

Autism and gut bacteria

A number of theories have emerged recently suggesting a possible role for abnormal components of the human gut microflora in the development of certain autistic characteristics.  It now seems increasingly likely that imbalances in the gut microflora and the development of autistic symptoms may be linked.  Certain unusual species of microorganisms are looking particularly suspicious.

Candida species

Candida normally constitutes only a very small proportion of the human gut microflora. Over 160 species of Candida have been identified.  They are described as ovoid budding yeasts that typically reproduce vegetatively and may exhibit hyphae. Competitive inhibition and certain immune functions normally keep growth under control.  Previous research has led some groups to suggest that certain autistic characteristics may partially be a consequence of an overgrowth of Candida.  Well-documented effects of a Candidia overgrowth can include vitamin deficiencies, fatty acid deficiencies, chronic CO₂ and ethanol production, and possibly most importantly, some Candida species are known to produce a whole range of toxins.  The symptoms that result vary widely, but can include fatigue, mood lability, depression, inability to concentrate, headaches, loss of energy, food cravings, mold sensitivity, multiple food and chemical intolerance and neuropathic problems.  The question of how the overgrowth starts is often relatively simple.  Many parents of autistic children tell of how multiple courses of antibiotics are often prescribed to their children.  This is often for illnesses early in life such as ear infections.  However after hundreds of rounds of antibiotics (presumably because of secondary infections or the illness didn't clear up) the normal protective bacteria simply do not exist in the gut.  This provides a perfect set of conditions for the Candida to thrive. 

Treatments for a yeast overgrowth typically take the form of antifungal drugs such as nystatin or diflucan.  Following the start of anti-fungal treatment, patients often exhibit a transient worsening of symptoms.  This reaction is rarely an allergic reaction; it is possibly a systemic 'Herxheimer' reaction due to the rapid killing of Candida cells.  Values for microbial metabolites often increase dramatically during the immediate period.  However levels then fall after 4 days to two weeks.  This is a systemic reaction due to the rapid killing of yeast and the consequent absorption of large quantities of fragmented yeast products.  Controlling a Candida overgrowth and recolonisation of the gut with beneficial and protective bacteria such as lactobacilli and bifidobacteria may help alleviate some symptoms of autism.

Further Reading:
Shaw, W., Kassen, E. and Chaves, E. (1995) Increased excretion of analogs of Krebs cycle metabolites and arabinose in two brothers with autistic features. Clinical  Chemistry 41: 1094-1104
Shaw W, (1999) Role for certain yeast and bacteria byproducts discovered by organic acid testing in the etiology of a wide variety of human diseases. Bulletin of The Great Plains Laboratory. Overland park, KS 66204 (913) 341-8949

Clostridia species

Ellen Bolte (1998) outlined the possibility of a subacute, chronic tetanus infection of the gut as an underlying cause of autism in some individuals.  Extensive antibiotic use creates a favourable environment for colonisation by opportunistic pathogens.  Clostridium tetani is a ubiquitous anaerobic bacillus known to produce a potent neurotoxin.  The normal site of binding for the toxin is the spinal cord.  However, the vagus nerve is capable of transporting tetanus neurotoxin, thus providing a route of ascent from the intestinal tract to the central nervous system and thus bypassing the spinal cord.  Once in the brain this may disrupt the release of neurotransmitters.  This may explain the characteristics of some autistic symptoms.  More recent studies by Dr Sydney Finegold have given us a more extensive insight into the possible role of clostridia in Autism. The number of clostridia species found in the stools of autistic children and control children were assessed.  In all, the autistic children had eight species of clostridia not found in the controls whereas the controls only yielded three species not found in the autistic subjects.  Overall levels of clostridia and ruminocoocus species were higher in the stools of the autistic subjects and upon identification it was found that one or more of the species found only in the autistic children were toxin producers. 

The significance of this finding should not be underestimated.  When a group of autistic children were treated with oral vancomycin or metronidazole improvements were noted in both social interactions and intellectual function as determined by blinded review of videotapes.  The children regressed within two weeks of discontinuing therapy.  The vancomycin was effectively used as a probe drug to help determine whether or not the hypothesis was valid.  Seemingly it was - the group is now planning some double-blind placebo controlled studies to look at the usefulness of antimicrobial therapies.

Further Reading:
Bolte ER, (1998).  Autism and Clostridium tetani.  Medical Hypotheses 51(2): 133-144.
Sandler RH, Finegold SM, Bolte ER, Buchanan CP, Maxwell AP, Vaisanen ML, Nelson MN, Wexler HM (2000).  Short-term benefit from oral vancomycin treatment of regressive-onset autism.  Journal of Child Neurology 15(7): 429-435.
Finegold SM, Molitoris D, Song Y, Liu C, Vaisanen M-L, Bolte E, McTeague M, Sandler R, Wexler H, Marlowe EM, Collins MD, Lawson P, Summanen P, Baysallar M, Tomzynski T, Read E, Johnson E, Rolfe R, Shah H, Manning P and Kaul A (2002).  Gastointestinal Microflora Studies in Late onset autism.  Clinical Infectious Diseases. In press.

Indole acryloglycine (IAG)

Indole acryloglycine (IAG) is a metabolic product of the amino acid tryptophan and can be found in trace amounts in the urine of apparently normal healthy individuals.  It was first described in the urine of a patient with a light sensitive dermatitis in 1958. A number of groups have described its presence in the urine in a variety of dietary disorders and each proposed that the presence of unusual bacteria in the gut might be responsible.   More recently the work of Dr Paul Shattock of the Autism Research Unit, University of Sunderland, has shown the presence of IAG in the urine of a number of subjects diagnosed with autistic spectrum disorders.

So what is the significance of this unusual metabolite? 

Under normal conditions tryptophan is converted to indole pyruvate and indole acetate and can be detected in the urine of normal subjects.  Elsden et al(1976) discussed the end products of metabolism of aromatic amino acids including tryptophan by clostridia species. More recently Smith and Macfarlane (1997) carried out similar studies in anaerobic batch cultures and were able to investigate the effects of pH and carbohydrate availability on the production of toxic metabolites. Here it was proposed that under certain abnormal gut conditions, anaerobic coliforms can convert trytophan to indole proprionic acid, which is subsequently absorbed and oxidised to indole acrylic acid and conjugated in the liver to indole acyloglycine (IAG).

Szeinberg et al(1965) reported the disappearance of IAG from the urine of a patient given neomycin who had previously excreted large amounts of the compound.  Following completion of the course of antibiotics and discharge from hospital the IAG reappeared in the urine.  They concluded that the production of IAG was likely to be mediated by unusual gut bacteria and that it was probably passed between members of the family of the patient.

Paul Shattock and Dawn Savery have estimated (although they admit crudely) that about 75% of subjects with autism exhibit the presence of IAG in the urine.  Interestingly they have also estimated that about 50% of fathers, mothers and siblings show unusually high levels of IAG.  Shattock and Savery have suggested that IAG represents a detoxified version of a parent compound that may affect the permeability of membranes throughout the body.  This is significant since we know that many autistic subjects are affected by opiate substrates and other unusual dietary factors because of problems with the permeability of membranes in the gastrointestinal tract and other organs.  With this knowledge, we may be able to set about managing the appearance of IAG and other unusual metabolites in the urine of affected subjects and affect a consequential improvement in symptomology. 

Further Reading:
Shattock P, Whitetley P, and Savery D (2001).  Autism as a metabolic disorder: Guidelines for gluten and casein - free dietary intervention, 2^nd Edition. Sunderland: Autism Research Unit, University of Sunderland, UK

Managing the Gut Bacteria

So we are now fairly confident that something unusual might be going on with the gut bacteria in autistic children.  The natural question is what are we going to do about it?  Part of the work of the Food Microbial Sciences Unit is molecular tracking of gut bacteria populations and the development of dietary procedures that target the gut bacteria to help us manage these populations so they become more beneficial and protective.  These tools are probiotics and prebiotics.  In simple terms probiotics are the beneficial bacteria and prebiotics are their lunch.

Examples of probiotics are lactobacilli species and bifidobacteria species.  These are live microbial feed supplements which beneficially affects the host.  Many different strains are used including Lactobacillus acidophillus, Lactobacillus casei, Bifidobacterium bifidum andLactobacillus plantarum.  A number of clinical trials have been completed and various mechanisms for their effectiveness have been proposed.  In terms of Autism and ASD's it has been suggested that probiotic supplementation is useful following anti-fungal treatments - since once the yeasts have been destroyed, the resulting gap is then recolonised with beneficial and protective bacteria.  However the barriers to success are seen as quite high since the bacterial cells must survive intact such obstacles as transportation and temperature abuses, stomach acid, bile secretions and competitive inhibition once in the gut.

The alternative approach is that of prebiotics.  These are non-digestible food ingredients that selectively stimulate a limited number of bacteria in the colon to improve host health.  Prebiotics are thought to selectively stimulate the beneficial bacteria (e.g. lactobacilli and bifidobacteria) and selectively inhibit non-beneficial organisms that may cause intestinal upset or other gut problems.  Importantly, prebiotics can inhibit pathogen colonisation in the gut by competitive inhibition.

The relationship between the health of the gut and beneficial and protective bacteria has been known for many years. Recolonisation of the gut with beneficial bacteria is the aim following the removal of pathogenic bacteria.  Prevention of colonisation by non-beneficial bacteria is necessary.  Probiotics may not survive or re-colonise the gut on their own.  Prebiotics may help boost their ability to recolonise in the autistic gut.  Both may provide the host with adequate protection from recolonisation by pathogenic microorganisms (such as candida or certain gut anaerobes.  A transient improvement in the gut environment may be seen.  A transient improvement in autistic symptoms may be seen.  The chances of recolonisation by pathogenic bacteria and subsequent relapse of symptoms may be reduced.

Further Reading:
Gibson GR and Roberfroid MB (1995).  Dietary Modulation of the human colonic microbiota: Introducing the concept of prebiotics.  Journal of Nutrition 125: 1401-1412.
Gibson GR, BerryOttaway P and Rastall RA (2000).  Prebiotics: New Developments in Functional Foods.  Chandos Publishing Limited, Oxford. 

Current Research at Reading

The Food Microbial Sciences Unit is now looking to start some preliminary research into the diversity of gut bacteria of autistic spectrum disorder children.  Using a recently developed molecular technique called FISH, we can identify and quantify a whole range of bacterial and yeast species from a faecal sample.  By doing this we hope to try to understand how differences in gut bacteria populations relate to autistic symptoms. We are hoping to recruit a number of autistic and autistic spectrum disorder children to take part in this study.  Very simply, all that is required is the completion of a short questionnaire and the collection of one fecal sample from your autistic child.  If you wish to take part in the study, you will be provided with the necessary equipment and sampling tubes and full instructions on how to collect a sample.  It’s very easy to do and it will mean that you receive a detailed description of the fecal gut bacteria found and a full explanation of what it all means. The best part is that taking part is completely free.  If you are interested in participating, you can contact the AutismFile for more details. 

Our future work is likely to take us into many different areas of the Autistic Spectrum.  We will be using a number of different techniques in the near future to help us understand in much more detail the nature of the gut bacteria populations in the autistic spectrum.  It is likely that we will want to recruit some volunteers for more detailed work.  If you are interested in taking part please contact the AutismFile.