Tuesday, 28 June 2011

Asthma and autism

I recently attended a conference which gave me great hope. Hope that our contemporary model of autism and quite a few other behaviourally-defined conditions as somehow being 'stand-alone' entities is shifting and adapting as all good models should. Incorporating the fact that autism, whilst being an important diagnosis, does not seem to confer any protection against developing or presenting alongside other more somatic conditions.

I have discussed this issue on several other posts relating to things like diabetes, overweight and obesity, etc. The crux of the problem seems to be that a diagnosis of autism might be a barrier to receiving screening or treatment for these other conditions if co-morbid, as it also appears to be the case for conditions like schizophrenia for example. In this post I turn my attention to another big health issue for many people, asthma, and its links (or not) to autism following on from my recent post on allergy and intolerance.

Conceptually at least, asthma and autism share some commonality. Both are what I would term a 'cloud' condition. That is, you can see the cloud in the sky and so know it is there, but determining where the edges of  the cloud are, where the cloud starts and finishes, takes a little bit more of an effort particularly when there are lots of clouds in the sky. So it is with autism. Asthma is a bit of a catch-all terms used to describe various symptoms such as wheezing, breathlessness and coughing; most people will have at some point in their lives have presented with one or more of these symptoms for one reason or another although it is the frequency and timing of symptoms that seems to be important in diagnosis. Definitions of asthma are abound but very few (if any) places provide specific guidance on how to categorise severity or frequency as part of asthma descriptive guidelines.

Although a chronic inflammatory condition associated with acute phases, when it comes to the question of what causes asthma and how does the disease manifest physically, there are still quite a few gaps in the evidence base. Asthma UK have some excellent information about all things asthma here. It is known that inflammatory processes are connected to airway remodeling as a result of increased mucus secretion, a thickening of the airway membrane and enlargement of the smooth muscle mass. In cases of fatality which unfortunately there are in asthma, the finding of a mucus plug, consisting of mucus and various immune cells including our old friends the eosinophils, is often present.

An estimated 5.2 million people in the UK are currently receiving treatment for asthma including just over a million children and young adults and the figures aren't much better in the US either. An important aspect of controlling asthma alongside preventative and relief inhalers is the identification of trigger factors leading to the exacerbation of symptoms. A variety of trigger factors have been suggested for asthma, ranging from foods to exercise to environmental pollutants to animal hair. Like other 'allergic' diseases, the trigger factors vary from person to person.

So what about asthma in cases of autism?

Well as you might imagine there has been some work done looking at various aspects of the two conditions and in connection to some surprisingly interesting areas. The basics first: prevalence of asthma in autism? Well that's a bit of a tough one because as things stand at the moment, I can't actually find any reliable data on this. The best I can say is that yep, both conditions are showing an increase in prevalence over the past few decades and by my 'autism is not protective against other conditions' rule of thumb, I would argue that very little tells me that asthma prevalence rates are any lower in autism than they are in the wider population although I might be wrongThis paper provides quite a good overview of how the two conditions perhaps share some interesting characteristics in terms of genes and environment touching also upon that prevalence issue.

Although I am quite wary of the concept of 'risk' particularly when applied on a population-level, there is some suggestion that familial asthma and allergy might increase the risk of autism or intellectual disability in offspring, possibly as a function of either exposure patterns or as a result of a more generalised relationship with autoimmunity. Carrying on the theme of risk, this study suggested, amongst other things, that an early asthma diagnosis might be tied into later diagnosis of autism influenced also by levels of airborne phthalates. I have to admit that I am intrigued by this proposition particularly given the recent focus on pollutants and risk of autism; intrigued but not yet thoroughly convinced by the data presented so far. Medication has also been speculatively linked to asthma and autism; this paper suggesting that acetaminophen (paracetamol to us UK folk) use may be linked, although I note that the original assertions linking asthma to such analgesic use is coming under further scrutiny. Various other classes of medication used for the management of asthma have similarly been suggested to be linked, although please remember correlation does not imply causation.

Another area that cropped up on my various searches for this post was the possible common link with the so-called leaky gut (gut hyperpermeability if I am to be factually correct). One of my favourite papers from recent years by Liu and colleagues discusses how increased intestinal permeability is a common denominator in many conditions including autism, type-1 diabetes and also asthma. The precise reasons why such intestinal hyperpermeability is present and related (or not) to conditions like asthma is unknown; whether due to more generalised connective tissue problems or whether providing a route through which antigens could trigger asthma or suggesting involvement for the whole mucosal immune system in asthma - there remain some questions to be answered.

I would perhaps conclude from the data that there may be some interesting relationships between asthma and autism which need further investigation. I have not touched upon the issue of asthma management in relation to autism and whether medication and compliance are affected by core and peripheral autistic symptoms for example.

To end this post there is no link to a music video or funny picture but rather I am going to be serious for a moment and link to some information on what to do during an asthma attack as provided by Asthma UK. This is advice from them not from me. Hopefully you will never need to use it.

[Update: March 2014: Readers might also wish to read my post titled: 'Asthma as a risk factor for autism?']