Thursday, 2 February 2012

The geography of autism: urban or rural?

A short sentence in the abstract to a paper by Kiani and colleagues* caught my attention recently. The paper reported on the distribution of autism spectrum and other conditions in the UK according to defined designations of geographical location. In other words, whether there were any differences in reported rates according to whether people were living in a rural or an urban area. The authors suggested that among their sample (N=2713), autism spectrum disorders in particular, were more common in people living in rural areas.

I was interested in this work for several reasons. Quite a few years ago an undergraduate psychology student - 'Big bad BB' (you know who you are) - came and did some work with us involving pin-mapping where people with autism and related conditions resided on a large map of the UK. I need to track down the results which were published as conference proceedings to check but I faintly remember some interesting 'trends' emerging from this data not entirely dissimilar from the current paper.

Of course there could be lots of reasons to account for the reported results. Socio-economic status, where people work, or just a wish for a bit of quiet and tranquillity are a few factors. Those of you who regularly read this and my other blog might also pick up a bit of interest in the 'chemical world' around us, and in particular the various descriptions of exposure patterns and relative risk of lots of things. Suffice to say that when I think about rural areas and countryside, apart from rolling hills and cows and sheep chewing the cud, I unfortunately also tend to think 'pesticides'.

I'm not on this occasion going to get too alarmist based on the findings of the current paper. Trawling back through the research archives, the data is fairly mixed when it comes to asking the question 'where do you live' with regards to autism. This paper based on Taiwanese data suggested that residing in rural parts was actually less likely to get you an autism diagnosis than being an urban dweller but there again, rural Taiwan might not be the same as rural England or rural elsewhere. Data from Western nations do point to 'urbanisation' as being a potential contributory factor in the increasing numbers being diagnosed with autism. Remember freeways (motorways in England) and autism? Bear also in mind that (a) where you currently live is not necessarily the same as where were you born or where your parents lived before you were born and (b) very few people tend to live in city centres, at least here in the UK; more often than not you get a doughnut effect in terms of residence being outside of a hollow built-up city centre.

That all being said I'm not ready to discount the current results as an artifact or fluke just yet. The study by Roberts and colleagues** published a few years back which suggested that pregnant women living close to sprayed fields had a six-fold increase in later offspring diagnosis of autism comes to mind. Having done a little bit of reading on the persistence and potential effects of things like pesticides, it is perhaps unwise to rule out any 'environmental' factor in relation to autism, at least some cases of autism, just yet. Certainly here in the UK, the potential health implications of pesticide exposure seems to still be on the research menu as per this study description by Galea and colleagues***. We await their findings.

[Update 15/02/12: Found the pin-mapping data we undertook. A poster presentation 'UK Autism Demographics' Budd, B. 2000: Autism: perspectives on progress. University of Durham. pp.207-214. Yes, proportionally more people with autism living in rural areas based on analysis of 784 people with autism in the UK (1996-2000)].

* Kiani R. et al. Urban–rural differences in the nature and prevalence of mental ill-health in adults with intellectual disabilities. Journal of Intellectual Disability Research. February 2012.
DOI: 10.1111/j.1365-2788.2011.01523.x

** Robert E. et al. Maternal residence near agricultural pesticide applications and autism spectrum disorders among children in the California Central Valley. Environmental Health Perspectives. 2007; 115: 1482-1489.
DOI: 10.1289/ehp.10168

*** Galea KS. et al. Biological monitoring of pesticide exposures in residents living near agricultural land. BMC Public Health. November 2011.
DOI: 10.1186/1471-2458-11-856