In the eternal search for the various potential factors (yes, there are probably going to be several) to account for the quite staggering increases in diagnosed cases of the autism spectrum conditions, no stone is seemingly being left unturned. Accepting the important and oft-cited sentence "correlation is not the same as causation" and accepting that the reasons for the increase in the autisms (plural) might differ from location to location, country to country and people to people, retrospective reviews of registries and case notes have featured quite a bit in this search for reasons.
The paper by Suzanne Bolton and colleagues* follows in this methodological tradition, suggesting: "an observation of increased rates of ASD [autism spectrum disorder] among a migrant population derived particularly from children born to mothers originating in Sub-Saharan Africa" based on a review of some 366 children presenting at a child development service in Ireland (Éire).
Based on those 366 case reports, autism or rather an ASD, was diagnosed in 131 and speech and language issues in 132 children. This in itself is interesting data based on the proportion of children coming to use the child development services - I assume because someone, somewhere had observed something worthy of the referral - and those eventually diagnosed with autism. Even more interesting in light of further genetic connections being made between autism and language impairment**.
No mind, when looking at those born to mothers born themselves in Africa "a higher proportion of the African cohort 13/18 (72.2 %) presented with moderate/severe cognitive disability compared to the Irish group 9/55(16.3 %)". In other words, the presentation of autism and intellectual (learning) disability towards the more severe end of the spectrum seemed to be more pronounced in the migrant population than those born to mothers themselves born in Ireland.
This is not the first time such a finding has been reported. I hark back to my post on the work of Cecilia Magnusson and colleagues*** who also reported a similar trend in their registry-based study following on from similar suggestions from other work.
So, what might one surmise from this growing body of work. Well, if I were to use the paper by Rai and colleagues**** as my starting point (see a previous post here) I might say that we should be looking at factors such as socio-economic status (SES) among those families arrived from Africa compared to Irish families to see if they could account for the differences raised by Bolton et al. Rai concluded that "Lower, not higher, socioeconomic status was associated with an increased risk of ASD" and without making any sweeping generalisations, one has to wonder whether demographic disparities might exist on the basis of indigenous and naturalised status.
That all being said, Ireland has some pretty comprehensive measures when it comes to the screening and diagnosis of autism (see here) no matter what side of the border you are on. If we are talking about children presenting with "a more severely affected" type of autism, it's highly likely that if not parents, nursery or school or other services would pick up on the need for a referral for assessment even if not knowing that it might be autism. Language and cultural differences about autism (see here) may impact on this process but I'd hazard a guess that not as much as one might first think.
Other potential explanators please. Well, without getting too bogged down in the debate about different ethnicities and different genetics, one has to wonder whether the risk of autism might be somehow reduced or elevated among different peoples. At the moment, we can't say for sure because worldwide, not everyone has access to the same screening, assessment and diagnostic resources that we perhaps take for granted in the modern Western world (see here). Autism research is also not exactly thriving in some parts of the world. Throw in again those language and cultural issues - even in our supposedly developed world***** - and the big question mark on this area still remains.
Then to environment. Lots of potential factors here including the stress of moving to and integrating into a new country, the introduction of a very new environment and climate - Ireland vs. Sub-Saharan Africa, mmm? - new foods, new microbes/infections, etc. Take your pick of what might be important or not. With my current interest in all things sunshine and vitamin D, I'm minded to suggest that this might be a factor worth considering given all the research attention that has been paid to vitamin D and autism. That and the whole solar intensity and ADHD link (no, really).... Likewise, I'm sure lessons can be learned from other research highlighting a similar pattern of risk in relation to other conditions such as schizophrenia and its link to immigration status******.
Whatever the reasons for the disparity being highlighted by the studies by Bolton and others, from a practical point of view it is perhaps more important that measures are put in place to accommodate this potentially heightened risk of offspring autism in immigrant populations. This might mean additional screening and assessments being offered to communities (language-appropriate) as well as providing any advice and education that may be required about autism and raising a child with autism.
And while we're on the topic, I'll also throw the paper by Lehti and colleagues******* (open-access) into the mix and their suggestion that "In Finland, children who are born to immigrant mothers with or without an immigrant partner, have an increased risk of childhood autism".
* Bolton S. et al. Autism in a recently arrived immigrant population. Eur J Pediatr. 2013 Oct 2.
** Bartlett CW. et al. A Genome Scan for Loci Shared by Autism Spectrum Disorder and Language Impairment. Am J Psychiatry. 2013.
*** Magnusson C. et al. Migration and autism-spectrum disorder: population-based study. British Journal of Psychiatry. February 2012. DOI: 10.1192/bjp.bp.111.095125
**** Rai D. et al. Parental socioeconomic status and risk of offspring autism spectrum disorders in a Swedish population-based study. J Am Acad Child Adolesc Psychiatry. 2012 May;51(5):467-476.e6.
***** Zuckerman KE. et al. Pediatrician Identification of Latino Children at Risk for Autism Spectrum Disorder. Pediatrics. 2013; 132: 445-453.
****** Cooper B. Immigration and schizophrenia: the social causation hypothesis revisited. Br J Psychiatry. 2005; 186: 361-363.
******* Lehti V. et al. The risk of childhood autism among second-generation migrants in Finland: a case--control study. BMC Pediatrics 2013, 13:171
Bolton S, McDonald D, Curtis E, Kelly S, Gallagher L. (2013). Autism in a recently arrived immigrant population Eur J Pediatr DOI: 10.1007/s00431-013-2149-6