A role for viral infection in the aetiology of coeliac disease?

"In this longitudinal study, we found that a higher frequency of enterovirus infections was associated with increased risk of coeliac disease."

So said the findings reported by Christian Kahrs and colleagues [1] (open-access available here) based on the results of their: "Case-control study nested within Norwegian birth cohort recruited between 2001 and 2007 and followed to September 2016."

Following the screening of some 47,000 infants for the 'genetics of coeliac disease' - HLA genotype DR4-DQ8/DR3-DQ2 - over 900 children were entered on to the study. This group were followed "with repeated blood and faecal samples from the age of 3 months" for quite a few years. Just over 500 participants who quite regularly donated blood samples, were asked if they wanted a screen for coeliac disease. Two hundred and twenty of them (or their parents/guardians) said 'yes please' and the study results were drawn from this group. Twenty seven of the 220 participants with those all-important coeliac risk genes were diagnosed with the condition. Twenty five of those 27 diagnosed with coeliac disease were matched against 50 of the no coeliac disease participants; matching was done "for duration of follow-up, date of birth, and county of residence." It was then just a case of looking at all the biological data that had been accrued from those blood and fecal samples to ascertain things like (a) "the time interval when cases seroconverted for coeliac disease markers" (i.e. when the antibodies diagnostic of coeliac disease began to be present) and (b) if and when enterovirus was detected in some of the samples (stool samples) via PCR (polymerase chain reaction).

Results: as shown in the supplementary material, the mean age at first presence of coeliac disease (CD) antibodies in the CD diagnosed sample (n=25) was around 42 months (when the first positive sample was recorded). Symptoms 'debut' was around an average age of 73 months and CD diagnosis was received on average at 87 months. Enterovirus was reported in both CD (n=25) and non-CD groups (n=49). Some 20% of the stool samples from the CD group were positive for some kind of enterovirus exposure compared with 16% of controls. Slightly more enterovirus positive stool samples were observed in the CD group (median 4 positive samples per child) than the control group (median 3 positive samples per child).

As per the opening quote to this post: "Enterovirus was found in 370 (17%) of 2135 samples and was significantly more frequent in samples collected before development of coeliac disease antibodies in cases than in controls." Further: "The association was restricted to infections after introduction of gluten." In other words, there seemed to be some evidence of a possible temporal connection between enterovirus and the development of CD, suggesting that enterovirus exposure and not gluten was the more important trigger for CD.

Mechanisms? Well, there's some speculation about that in the Kahrs paper and a: "plausible explanation is that enterovirus causes impaired barrier function, which in turn increases the risk of coeliac disease." Enterovirus causing impaired intestinal (gut) barrier function eh? Interesting, does that mean 'leaky gut' might have a viral origin in some cases? Mmm, that could have lots of implications...

Obviously more investigation is required in this area. The Kahrs study has some strengths in terms of the sample collection protocols and frequency and potentially establishing a temporal *link* between CD and enterovirus exposure. But there's still more to do: "unmeasured confounding factors or residual confounding can never be entirely ruled out in non-randomised studies." But don't let that take anything away from the potential importance of these findings.

And on the topic of prospectively following children who might be prone to develop coeliac disease, the study findings published by Lionetti and colleagues [2] are equally interesting. In particular, based on 23 of their 26 children who received a "potential diagnosis of CD" but nonetheless "continued a gluten-containing diet... 19 (83%) became antibodies negative at 1 year from the first biopsy and remained negative up to 10 years of follow-up." Could there be a tie-up with the Kahrs findings perhaps?

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[1] Kahrs CR. et al. Enterovirus as trigger of coeliac disease: nested case-control study within prospective birth cohort. BMJ. 2019 Feb 13;364:l231.

[2] Lionetti E. et al. Long-Term Outcome of Potential Celiac Disease in Genetically at-Risk Children: The Prospective CELIPREV Cohort Study. J Clin Med. 2019 Feb 5;8(2). pii: E186.

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On gut bacteria and depression

I'm kinda standing on the shoulders of giants with this post talking about the findings reported by Mireia Valles-Colomer and colleagues [1]. An editorial published in Nature [2] to coincide with the publication of the Valles-Colomer paper says just about everything that needs to be said on this research, which observed that: "Gut–brain module analysis of faecal metagenomes identified the microbial synthesis potential of the dopamine metabolite 3,4-dihydroxyphenylacetic acid as correlating positively with mental quality of life and indicated a potential role of microbial γ-aminobutyric acid production in depression." Yes folks, the idea that "microorganisms in the human gut could influence the brain" is moving from 'wild idea' to "wise pursuit".

The sequencing of DNA from donor stool samples as part of the Flemish Gut Flora Project ('You too are a walking bacteria colony' is the strap line) was the starting point for the Valles-Colomer study; stool samples provided by over 1000 participants. Researchers also accessed data on both self-reported and "physician-diagnosed depression" and set to work looking for any potentially important correlates between bacteria and psychology. The words "with validation in independent data sets (ntotal = 1,070)" are also (importantly) mentioned in the Valles-Colomer paper. Oh, and they also "mined the data to generate a catalogue describing the microbiota’s capacity to produce or degrade molecules that can interact with the human nervous system."

Results: "Butyrate-producing Faecalibacterium and Coprococcus bacteria were consistently associated with higher quality of life indicators." There's that word again: butyrate and yet more positive publicity for this compound (see here) and it's standing reaching almost 'bacterial sainthood'. Researchers also observed that two groups of bacteria were also reduced in those with depression: Coprococcus and Dialister alongside observing that this finding held "even after correcting for the confounding effects of antidepressants [use]." And then there was that 3,4-dihydroxyphenylacetic acid, also called DOPAC, finding, a metabolite of the neurotransmitter dopamine. I have actually mentioned DOPAC before on this blog (see here) in relation to what happens when rats are subjected to 'early immune stimulation' [2]. I don't think there is much overlap between that rat study and the Valles-Colomer paper (that rat paper was looking at DOPAC levels in brain tissue for example) but the suggestion from the authors that DOPAC levels were "correlating positively with mental quality of life" requires quite a bit more investigation.

Caveats? Well, out of their initial 1054 participant cohort, only 121 participants had "GP-reported depression." About half of these participants were taking antidepressants for their depression, the others weren't. The participant numbers aren't exactly tremendous for this portion of the study. Similar to something mentioned in other research (see here), I'm also minded to suggest that future research might perhaps consider looking at multiple stool samples taken over different occasions for the same person. This would perhaps establish whether gut bacterial populations are stable and whether that stability translates into stability of something like depressive symptoms too. I am likewise cautious that we don't jump ahead of ourselves here in terms of important issues like cause-and-effect and for example; whether there may be other important 'influencers' of gut bacteria when it comes to depression (see here and see here).

Lots more study is required on the suggestion of a gut bacterial *link* to depression [3], including that focused on the mechanics of any relationship (e.g. any involvement of the vagus nerve). If the link is further established, there are a number of potentially important implications: the possibility of a 'bacterial transferability hypothesis of [some] depression' (see here), intervention options focused on redressing balance in bacterial colonies (see here) and what such findings might do for the whole 'gut-brain axis' idea.

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[1] Valles-Colomer M. et al. The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology. 2019. Feb 4.

[2] Editorial. Links between gut microbes and depression strengthened. Nature. 2019. Feb 4.

[3] Cheung SG. et al. Systematic Review of Gut Microbiota and Major Depression. Front Psychiatry. 2019;10:34.

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The gut microbiome and autism... so far (continued)

Building on other reviews of the peer-reviewed science literature looking at the intestinal microbiota in relation to autism (see here), the paper published by Feitong Liu and colleagues [1] provides an updated 'where we're at' position in relation to the "potential evidence for the characteristic dysbiosis of gut microbiota in ASD [autism spectrum disorder] patients compared with healthy controls (HCs)." Just before you say anything, those are the authors words not mine; I'm not a fan of the word 'patients' nor use of the term 'healthy control' to denote not autism - not autistic, but there you go.

Language use aside, the Liu paper covers quite a lot of the peer-reviewed science talking about gut bacteria and autism up to March 2018. Their systematic review took in data from 16 studies - human studies "that compared the composition of gut microbiota in ASD patients and HCs using culture-independent techniques." Researchers had also previously registered their intention to conduct this review as per their PROSPERO entry (see here).

So what did their systematic review reveal? Well, they talked about how most studies looked at the intestinal microbiota via the examination of stool samples, although a couple relied on gut biopsy samples instead. Coincidentally, I spotted a bit of an error in the Liu paper in relation to their study reference numbering in one of the results sections, and how the Luna study (see here) and Williams study (see here) which relied on biopsy samples were replaced by other 'stool as a sample media' studies in the Liu write-up. It's only a small point and doesn't detract from the paper overall. The included studies also covered various different populations in a geographic sense as well as taking into account a mix of participants (with autism) in terms of the presence of gastrointestinal (GI) issues and the use of 'special' diets. Indeed, we are told that: "As restricted diet is very common in ASD patients, we tried to extract the information of eating habit in ASD and control group." Yes it is common, and yes it can have sometimes very negative effects (see here). Finally, all the studies included for review were "identified and assessed as medium (6–7) to high (8) quality" suggesting that the data were pretty reliable in a methodological sense.

Some key points emerged: "Overall, the changed structure of gut bacterial community in terms of β-diversity was observed coherently in ASD patients compared with HCs." Beta-diversity basically translates into 'between samples diversity' and in this case represents autism vs. not-autism controls. Out of the 16 studies included in their systematic review, Liu et al reported that "ten studies analyzed β-diversity (unweighted UniFrac distance, weighted UniFrac distances, and Bray-Curtis)." Six of those 10 studies "consistently reported that the microbiota of ASD patients clustered significantly apart from that of HCs." Ergo, there is evidence - some evidence - that the gut microbiome is significantly 'different' in autism compared with not-autism in a group sense. Some evidence at least.

Also: "Consistently, ASD patients had elevated abundance of Proteobacteria rather than HCs. In addition, Bifidobacterium, Blautia, Dialister, Prevotella, Veillonella, and Turicibacter were consistently decreased, while Lactobacillus, Bacteroides, Desulfovibrio, and Clostridium were increased in ASD patients relative to HCs."  Bear also in mind that Liu et al talked about various other bacterial species that were, in individual studies, elevated or depressed in the groups with autism, and how important such information might be. Such bacterial changes in terms of diversity or individual species predominating might also have knock-on effects as a result of the different chemical messages that different bacteria produce. One example: "Bacteroides is an abundant genus at all ages, from infants to adults. It is the main producer of propionate in the gut, and the abundance of propionate in feces correlates strongly with the abundance of Bacteroides." It probably won't surprise you to hear that propionic acid (propionate) has also got some research history when it comes to autism (see here) and indeed, with caveats, continues to do so [2]. Other examples are included in the Liu paper, including the 'chemical of the moment', butyrate (butyric acid) (see here). This complements other recently published research [3] too. And let's not forget how such bacteria and their chemical messaging also has some important 'effects' on things like gut barrier function and gut immune function, as part of the 'new triad' when it comes to autism and the gut (see here).

"Microbiome reconstitution could be a potential therapy to ASD patients in future." That's another topic raised in the Liu study on how "remodeling gut microbiota with diet, antibiotics, prebiotics, probiotics, and FMT [fecal microbiota transplant]" could be an option. Actually the future is now, as a quick scour of the autism research literature shows that some of these options are already being / have been investigated (see here and see here for examples). We do need a lot more information on the hows-and-whys of such therapeutic options; importantly covering safety, effectiveness and maybe highlighting the possible mechanisms involved, but there is already existing literature in this area.

As well as highlighting some of the shortcomings of the current research literature discussing the intestinal microbiota and autism, the Liu study provides a nice overview of this topic as things currently (up to March 2018) stand. Whether such information can eventually be 'manipulated' to improve things like quality of life in the context of autism remains to be seen...

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[1] Liu F. et al. Altered composition and function of intestinal microbiota in autism spectrum disorders: a systematic review. Translational Psychiatry. 2019; 43.

[2] Shams S. et al. Systemic treatment with the enteric bacterial metabolic product propionic acid results in reduction of social behavior in juvenile rats: Contribution to a rodent model of autism spectrum disorder. Dev Psychobiol. 2019 Jan 28.

[3] Wang M. et al. Alterations in Gut Glutamate Metabolism Associated with Changes in Gut Microbiota Composition in Children with Autism Spectrum Disorder. mSystems. 2019 Jan 29;4(1). pii: e00321-18.

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Low grade intestinal inflammation and autism

The suggestion that low grade intestinal inflammation might be related to some autism comes from the findings reported by Katarina Babinská and colleagues [1] (open-access available here).

Researchers set out to "assess the concentrations of fecal calprotectin in a sample of children with ASD [autism spectrum disorder] and to investigate the correlations of this inflammatory marker with the core behavioral symptoms of ASD."

Faecal calprotectin (FC) is a measure of the amount of calprotectin in a stool (poo) sample. It's typically released in response to the presence of inflammation and, here in Blighty at least, is indicated as "an option to support clinicians with the differential diagnosis of inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) in adults with recent onset lower gastrointestinal symptoms for whom specialist assessment is being considered." 

In terms of research history looking at autism and FC, there is some peer-reviewed science on the topic; also having been included as a parameter in the important paper by Laura de Magistris and colleagues [2] talking about 'leaky gut' in the context of some autism (see here) and how "FC was elevated in 24.4% of patients with autism and in 11.6% of their relatives." Such research is set in the more general context that bowel or gastrointestinal (GI) issues are absolutely no stranger to a diagnosis of autism (see here).

This time around Babinská et al measured FC (via ELISA) in some 87 children diagnosed with an autism spectrum disorder (ASD) aged between 2 and 17 years of age. The authors use the term 'low functioning' to describe this portion of their participant group but I'm rather less enamoured with such labels (see here) despite the well-deserved focus on a group very much under-represented in autism research and other areas. Alongside, over 50 age-matched controls (not-autism) and 29 siblings of children with ASD also provided samples for analysis and comparisons.

Results were not exactly as cut-and-dried as one might have expected. So: "In non-relatives significantly lower values of fecal calprotectin were observed than in both subjects with ASD and their siblings." What this means is that based on group results, those with autism and the siblings of those with autism seemed to manifest higher levels of FC than non-related controls. Based on individual results, where elevated levels of fecal calprotectin was set at 50 µg/g of feces or higher according to test producers guidance as being a level of concern, the frequency of such a finding was greater in those with autism (22%) and their siblings (20%) than in non-related controls (9%) but this difference was reported as 'non-significant'.

Authors also did a little work on another important area in relation to bowel symptoms/pathology and autism: how *might* something like intestinal inflammation 'interact' with the behavioural signs and symptoms of autism? Well, we are told that those diagnosed with autism "had to meet criteria for ASD" on two gold-standard diagnostic tools: the Autism Diagnostic Observation Schedule – second edition and the Autism Diagnostic Interview-Revised (ADI-R). Data from the ADI was examined in the context of the FC findings and lo and behold: "In the group with ASD significant correlations of fecal calprotectin with all domains of the ADI-R diagnostic tool were found: qualitative abnormalities in reciprocal social interaction and communication, restrictive and repetitive patterns of behavior." I say this bearing in mind that similar analyses between FC values and ADOS ratings do not seem to have been either done or reported on for some reason.

When the authors talk about low grade intestinal inflammation as potentially being relevant to some autism, they seem to be accurate insofar as the measured levels of FC in some participants and the *correlation* with autism scores on one of the gold-standard assessment instruments. That being said, there is quite a bit more to do in this area before anyone gets too carried away with the results as they stand. So for example, all that chatter about inflammatory bowel disease (IBD) being related to some autism (see here and see here) did not seem to register in this particular study insofar as the guidance on FC being a marker for possible IBD, albeit based on higher levels of FC being detected: "Active, symptomatic inflammatory bowel disease 200 – 40,000 mg/kg."

I also note that the authors report an important limitation when it came to their research: "Additional factors that might have been a cause of elevated FC levels, such as nutritional or gastrointestinal factors were not analysed." Nutritional factors eh? Y'mean like milk type for example [3] or other dietary and/or environmental factors such as the implementation of a gluten-free diet [4] positively affecting FC levels? Indeed, there are lots of potential factors that could cause a 'false-positive' when it comes to elevated FC such as infections like C. diff or gastrointestinal conditions such as coeliac disease, many of which have shown some important connections to autism (see here for example).

It looks like there is still much more research to do in this area but investigations should definitely continue.

To close, my brood have just discovered the brilliant film 'The Great Escape'. As well as setting up many, many discussions about war, bravery and captivity, they've also commented on the theme tune...

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[1] Babinská K. et al. Fecal calprotectin levels correlate with main domains of the autism diagnostic interview-revised (ADI-R) in a sample of individuals with autism spectrum disorders from Slovakia. Physiol Res. 2017 Dec 30;66(Supplementum 4):S517-S522.

[2] de Magistris L. et al. Alterations of the intestinal barrier in patients with autism spectrum disorders and in their first-degree relatives. J Pediatr Gastroenterol Nutr. 2010 Oct;51(4):418-24.

[3] Ho S. et al. Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study. Eur J Clin Nutr. 2014 Sep;68(9):994-1000.

[4] Balamtekın N. et al. Fecal calprotectin concentration is increased in children with celiac disease: relation with histopathological findings. Turk J Gastroenterol. 2012;23(5):503-8.

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