Monday, 21 January 2013

The skin-brain axis and autism?

I'm sure that many people with an eye on the autism research scene will have come across the term 'gut-brain axis' at some point in their reading. Denoting the suggestion of a possible relationship between what goes on in our deepest, darkest recesses and brain function (and onwards observed behaviour), the gut-brain axis has seemingly found a home particularly when looking at autism spectrum disorders.

Be it when it comes to describing the potential hows and whys of things like a gluten- and casein-free diet (potentially) showing some effects, or those quite consistent findings of elevated rates of gastrointestinal (GI) issues reported in at least a proportion of cases of autism(s), the gut-brain axis seems to be quite an enduring concept as it might also be in other conditions such as schizophrenia.

Axis not axes @ Wikipedia  
The specifics of the gut-brain axis have not however yet been fully elucidated; although quite a lot of speculation has focused on things like gut bacteria and intestinal permeability as showing some involvement; concepts which have cropped up on this blog quite regularly.

In this post I want to talk about another axis potentially relevant to autism and quite a few other developmentally defined or mental health related conditions: the skin-brain axis following the appearance of a rather interesting paper by Yaghmaie and colleagues* on mental health comorbidity in patients with atopic dermatitis.

A few points are worth noting given that I'm not able to post a link to the full-text paper:

  • This was a survey paper based on the US 2007 National Survey of Children's Health dataset (N=91,642). 
  • In short, the parents of children aged 0-17 years (0 years denoting those under 1 year old) were contacted and asked quite a few questions about the health of their children. 
  • For the purposes of this study, children with a history of atopic dermatitis (AD) as per the question: "during the past 12 months, have you been told by a doctor or other healthcare provider that XXX had eczema or any kind of skin allergy?" were asked about "provider-diagnosed mental health conditions" covering various diagnoses "previously been reported as associated with AD" and their results were compared with those without AD. Odds ratios (ORs) were calculated based on the risk derived from AD for various conditions.
  • The 12-month prevalence of AD for 2007 was 12.9%; a rise from previous estimates from data in 2003 (10.6%). Interestingly when comparing AD estimates state-by-state, California turned out to have the lowest AD prevalence (8.5%). Regular readers will know that in autism research terms, California has always been a bit of a focus (see here for example).
  • A diagnosis of AD was associated with an elevated risk of quite a few conditions: autism (OR: 3.04 CI: 2.13-4.34), ADHD (OR: 1.87 CI: 1.54-2.27) and conduct disorder (OR 1.87 CI: 1.46-2.39) among other things. All relationships were statistically significant when comparing AD and non-AD samples.
  • The authors also report that the severity of AD was also related to the likelihood of a developmental/mental health condition, in that the more severe the AD, the more likely a diagnosis was to be received.

Bearing in mind the nature and sampling methods of the Yaghmaie study, I have to say that I was taken aback by the findings of this paper and the potential implications. It's not that skin conditions have not been talked about with autism for example in mind before, as per the research base on things like psoriasis for example (see this post) and the whole autoimmunity side of things. Indeed, the atopy and allergy field has been mentioned quite a few times in autism research; alongside issues such as mast cell activation also being a source of speculation. But the implication that a skin condition like AD might actually raise the risk of developing autism or ADHD or a conduct disorder is a whole new ballgame on the mind-body relationship stakes bearing in mind the question of correlation-and-causation.

The authors also go as far as to suggest: "Strategies to prevent AD or to aggressively treat early skin inflammation might modify the risk of mental health disorders in at-risk children". This sentence really got me thinking. Thinking about inflammation and how this topic has been looked at on more than one occasion in autism research circles. Thinking about how skin and brain/behaviour might be linked, bearing in mind the source embryological material. Thinking also about the genetic - environmental factors which are linked to AD, and indeed going back to that gut-brain axis, how food might also play a role as per the link between gluten and dermatitis herpetiformis for example. Lots of thinking indeed.

The final words about the paper by Yaghmaie and colleagues should I suppose be ones of caution insofar as science needs to (a) replicate these findings, both in the US (home to participants) and outside the US, and (b) start looking in more details as to what the shared biological mechanisms and pathways could be (at least one authorship group have asked similar questions recently**).

That being said, this is yet more potential evidence for the whole-body nature of quite a few developmental and mental health conditions - remember the airways and autism research - and how autism research needs to keep expanding its scientific boundaries outside of the view that the grey (or rather pinkish) matter floating inside our skull is working completely in isolation.

Oh and perhaps I should also mention the meta-analysis by Schmitt and colleagues*** as adding more fuel to the correlation fire? And while we are on the topic of atopy, how about the paper by Chou and colleagues**** on allergic rhinitis and ADHD?

Stop now... and I will.

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* Yaghmaie P. et al. Mental health comorbidity in patients with atopic dermatitis. J Allergy Clin Immunol. December 2012.

** Denda M. et al. How does epidermal pathology interact with mental state? Medical Hypotheses. 2013; 80: 194-196.

*** Schmitt J. et al. Association of atopic eczema and attention-deficit/hyperactivity disorder - meta-analysis of epidemiologic studies. Z Kinder Jugendpsychiatr Psychother. 2013; 41: 35-44.

**** Chou PH. et al. Prevalence of allergic rhinitis in patients with attention-deficit/hyperactivity disorder: a population-based study. Eur Child Adolesc Psychiatry. December 2012.

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ResearchBlogging.org Yaghmaie P, Koudelka CW, & Simpson EL (2012). Mental health comorbidity in patients with atopic dermatitis. The Journal of allergy and clinical immunology PMID: 23245818