On migration status and offspring autism severity

"Black women from East Africa had more than 3.5 times the odds of autism spectrum disorder with intellectual disability in their children than Caucasian nonimmigrant women."

So said the study results reported by Jenny Fairthorn and colleagues [1] (open-access available here) providing yet more evidence for the need for much greater scrutiny as to why children of immigrant parents from East Africa are seemingly at higher risk of 'more severe' autism than other groups (see here and see here).

Based on data from "Western Australian state registries" (yet again), researchers set about comparing autism prevalence with and without intellectual (learning) disability as a function of various variables: race (ethnicity), immigrant status and region of birth of mothers of children. The authors really drilled down into the details on immigrants according to their birth region in this study.

Results: from a study sample of over 130,000 mothers, some 1000 had a child diagnosed with an autism spectrum disorder (ASD) together with intellectual disability (ID) and nearly 350 with a child with autism without ID. The figures equated to something like 0.7% of the total cohort with a child with autism and ID and 0.2% of the cohort with a child diagnosed with autism but not with ID. Authors also indicated that: "mothers of children with autism spectrum disorder with intellectual disability were more likely to be 40 years or more."

Then to some important data: "After adjustment for demographic factors and compared to nonimmigrant women, immigrant women were less likely to have a child diagnosed with either autism spectrum disorder with intellectual disability or autism spectrum disorder without intellectual disability." This finding covered various geographic locations from which migrant mums came together with their race/ethnicity. That is however, aside from mothers from East Africa, and that "three-fold higher odds of having a child identified with autism spectrum disorder with intellectual disability." Authors added that "all autism spectrum disorder diagnoses in the children of Black mothers were of autism spectrum disorder with intellectual disability" and that all cases "were from mothers born in East Africa, with four born in Ethiopia and one each from Eritrea, Kenya, and Somalia."

The authors acknowledge that their categorisations based on race/ethnicity and migration status led to some quite small group numbers being analysed (including not including any participants from other parts of Africa outside of East Africa). They also drew attention to the fact that their participant group of children with autism but without ID was quite a bit smaller than would be typically expected in comparison to the group with autism and ID (see here).

But the results do paint an interesting picture and particularly with regards to those from East Africa, where they are in line with what has been previously discussed in the peer-reviewed and lay literature. The question of 'why' is probably going to be a complicated one as the authors suggested that "at least some of this difference could be the result of various factors leading to higher ascertainment of autism spectrum disorder in this group of children." They also qualify that statement by saying that they "cannot rule out the possibility of some biological risk factor, such as nutrition or stress" being involved which opens up a role for variables such as vitamin D exposure for example (see here).

Personally, I think there are a few additional research directions that might need to be considered, primary among them is to have a little more detail on what autism prevalence might specifically look like in various areas of East Africa and Africa in general. I know this is a bit of a difficult ask in places where resources are really quite scarce, cultures are different (see here) and practical efforts for population screening are hindered by politics and the like. Until however we have such data, alongside some other important social and biological information, science doesn't have any 'baseline' measures on which to compare and contrast when it comes to families emigrating from such places and the possible reasons/changes that could be involved in this process and pertinent to offspring autism risk.

----------

[1] Fairthorne J. et al. Maternal Race-Ethnicity, Immigrant Status, Country of Birth, and the Odds of a Child With Autism. Child Neurol Open. 2017 Jan 12;4:2329048X16688125.

----------

Fairthorne J, de Klerk N, Leonard HM, Schieve LA, & Yeargin-Allsopp M (2017). Maternal Race-Ethnicity, Immigrant Status, Country of Birth, and the Odds of a Child With Autism. Child neurology open, 4 PMID: 28503625

On autism risk and immigrant status

"Fifteen studies suggest a higher prevalence rate of ASDs [autism spectrum disorder] among children of immigrants in comparison to native children."

Those fifteen studies formed a large part of the seventeen studies included in the review by Rafal Kawa and colleagues [1] who set out to look at the collected peer-reviewed literature on the topic of the "prevalence and risk for ASD in Europe among immigrants and ethnic minorities." Carried out as part of a European Union (EU) initiative titled 'Enhancing the Scientific Study of Early Autism' the Kawa review was a sort of first step to looking at whether the racial/ethnic disparities noted in autism rates in the United States for example, might also hold true for Europe. Evidently they did.

This is a topic covered before on this blog (see here for example) and so the results come as little surprise. One does have to be slightly cautious about how such data is interpreted, particularly in light of recent European history but outside of any politics there are some intriguing scientific questions posed by such data and some potentially important 'connections' with other independent datasets that could benefit autism research more generally (see here and see here). Given also some emerging research suggesting that autism may not be the only diagnostic label where risk is heightened according to immigrant status (see here), there are some further studies to be undertaken on this topic, in these days of overlapping labels (see here).

----------

[1] Kawa R. et al. European studies on prevalence and risk of autism spectrum disorders according to immigrant status-a review. Eur J Public Health. 2016 Dec 24. pii: ckw206.

----------

Kawa R, Saemundsen E, Lóa Jónsdóttir S, Hellendoorn A, Lemcke S, Canal-Bedia R, García-Primo P, & Moilanen I (2016). European studies on prevalence and risk of autism spectrum disorders according to immigrant status-a review. European journal of public health PMID: 28013245

Immigrant background and risk of offspring ADHD

"The likelihood of being diagnosed with ADHD [attention-deficit hyperactivity disorder] was significantly increased among children of two immigrant parents... and children of an immigrant father."

So said the findings published by Venla Lehti and colleagues [1] continuing a research theme from this authorship group (see here) on how immigration might, for various reasons, bring about an increased or decreased risk of certain behavioural and/or psychiatric outcomes. This time around ADHD was in the research spotlight and how analysis "based on a national birth cohort" numbering in the tens of thousands suggested there may be more to see when it comes to a diagnosis in light of parental immigration status.

The records of over 10,000 children/young adults born between 1991 and 2005 and diagnosed with ADHD by 2011 were compared with matched - not ADHD - controls (n=39,124) taking into account "parents' country of birth and native language." Various other variables were added into the subsequent statistical mix including "time since maternal migration." As per that opening sentence, there did appear to be more to see when it came to immigration status and offspring outcome; where a child was born to two immigrant parents, the adjusted odds ratios were not to be sniffed at (4.7, 95% CI 3.4-6.6) insofar as an increased risk of offspring ADHD diagnosis.

I was also taken by another finding reported by Lehti et al: "Children, whose parents were born in countries with low Human Development Index (HDI), were more often diagnosed with ADHD." The HDI is a sort of summary measure taking into account variables such as education, life expectancy and income ranking countries in terms of their human development. Quite a few of the countries in places like sub-Saharan Africa, North Africa and Latin America rank 'low' on the HDI and also seemed to tally with the specific data on country of origin when it came to the Lehti findings.

As interesting as the current findings are, the universal idea that ADHD risk might be elevated in children of immigrant families is by no means a settled issue [2]. As per my sentiments on quite a few issues covered on this blog, sweeping generalisations are not required. I would however like to see a lot more research done on this issue focused not just on 'risk' of diagnosis but also around the possible factors that might contribute to immigrant offspring being more readily diagnosed with something like ADHD. Lehti et al suggest that their results might indicate "increased exposure to environmental risk factors, differences in the use of health services, or challenges in diagnosing immigrants' children" as being relevant. Certainly one could draw on work in other clinical areas as being potentially relevant (see here for example) to the current findings including potential biological correlates too (see here and see here).

One further point that might also be particularly important to the Lehti findings: that linked to socio-economic status (SES) and how that seems to affect risk of a diagnosis of ADHD more generally (see here). Without generalising about any relationship between immigration status and SES, it is not outside the realms of possibility that at least for some migrants, entry to places like Finland where the current research was carried out, might not be accompanied by significant wealth for example. SES deprivation and ADHD diagnosis is an area of continuing interest [3]; indeed, with recent political situations in mind, one wonders whether future surveillance may be very much indicated.

----------

[1] Lehti V. et al. Association between immigrant background and ADHD: a nationwide population-based case-control study. J Child Psychol Psychiatry. 2016 May 2.

[2] Tan TX. Emotional and Behavioral Disorders in 1.5th Generation, 2nd Generation Immigrant Children, and Foreign Adoptees. J Immigr Minor Health. 2016 Mar 14.

[3] Russell AE. et al. The Association Between Socioeconomic Disadvantage and Attention Deficit/Hyperactivity Disorder (ADHD): A Systematic Review. Child Psychiatry Hum Dev. 2016 Jun;47(3):440-58.

----------

Lehti V, Chudal R, Suominen A, Gissler M, & Sourander A (2016). Association between immigrant background and ADHD: a nationwide population-based case-control study. Journal of child psychology and psychiatry, and allied disciplines PMID: 27133554

Vitamin D and autism: the story so far...

I don't want to keep you too long today aside from directing you to the literature review by Hajar Mazahery and colleagues [1] (open-access available here) discussing the collected peer-review literature on the topic of vitamin D and autism to date.


Anyone that stops by this blog might already know about my interest in the science around this issue (see here and see here for example) and how quite a few more resources really should be directed into this 'sunshine' research area. The Mazahery review pulls in the major themes included in the research literature including what has been published so far on levels of vitamin D and autism (and insufficiency/deficiency percentages), a possible role for ethnicity and migration, and use of vitamin D as a possible intervention option. They do also make mention of some of the genetics of vitamin D metabolism (see here) (and there is even more recent research on this [2]) and the potentially important link to areas such as autoimmunity with autism in mind (see here).

I'll leave you with their closing remarks: "Conclusions are not yet possible due to the inconsistent results, different methodological approaches employed, and very few trials in the current literature. However, there are some indications that early exposure to inadequate vitamin D may interact with other factors and contribute to the aetiology of autism, low vitamin D status might be highly prevalent in populations with ASD, and intervention with vitamin D might be beneficial in reducing autism symptoms among those who have ASD." That combined with what NICE here in England have already proposed more generally (see here) and you can perhaps see that vitamin D and the 'English Disease' (rickets) [3] might be but one connection for this important vitamin/hormone.

Oh, and as part of a wider group of variables 'linked' to autism, vitamin D is also discussed in the recent mini-review paper by Takeo Fujiwara and colleagues [4]. Thick and fast people, thick and fast...

And completely unrelated to today's post, IMFAR 2016 starts today.

----------

[1] Mazahery H. et al. Vitamin D and Autism Spectrum Disorder: A Literature Review. Nutrients. 2016 Apr 21;8(4). pii: E236.

[2] Coşkun S. et al. Association of polymorphisms in the vitamin D receptor gene and serum 25-hydroxyvitamin D levels in children with autism spectrum disorder. Gene. 2016 May 4. pii: S0378-1119(16)30361-4.

[3] Belton NR. Rickets--not only the "English disease". Acta Paediatr Scand Suppl. 1986;323:68-75.

[4] Fujiwara T. et al. Chemicals, Nutrition, and Autism Spectrum Disorder: A Mini-Review. Front. Neurosci. 2016; April 20.

----------

Mazahery H, Camargo CA, Conlon C, Beck KL, Kruger MC, & von Hurst PR (2016). Vitamin D and Autism Spectrum Disorder: A Literature Review. Nutrients, 8 (4) PMID: 27110819

Autism and low vitamin D at birth

Discussions about vitamin D (the 'sunshine' vitamin/hormone) and autism are not unfamiliar to this blog. Just last year (2014) I covered research talking about the possibility of a connection between vitamin D and [some] autism at least three times (see here and see here and see here), possibly more.

..but in my game, I'm the bad guy,
and I live in the garbage.

I wouldn't say that I'm an advocate for everything implied by the correlations being made between vitamin D levels and autism given that vitamin D levels have also been linked to everything from depression (see here) to schizophrenia (see here), issues which might also show some passing connection for some people on the autism spectrum (see here for example). But I am interested in how this research area is evolving...

And evolving it is, as yet another study has been published on vitamin D and autism, this time from Elisabeth Fernell and colleagues [1] (open-access) based at the University of Gothenburg in Sweden. Examining 25-hydroxyvitamin D (25(OH)D) levels in dried blood spots "taken in the neonatal period for metabolic screening", researchers concluded that: "low prenatal vitamin D may act as a risk factor for ASD [autism spectrum disorder]."

Aside from some happiness that the fantastic resource which is the neonatal blood spot is being put to good scientific use with autism in mind (see here), I was particularly interested to read about the findings from this research group given their previous foray in this area (see here) based on the paper from Kočovská and colleagues [2] (open-access). On that occasion they concluded that young adults diagnosed with an ASD were, as a group, quite a bit more likely to present with lower vitamin D levels than siblings, parents and an asymptomatic control group.

Back to the Fernell paper, and a few pointers might be in order:

• "The aim of the present study was to address the emerging hypothesis that low levels of vitamin D at birth increase the risk for ASD." OK.
• Sibling pairs were used, one child diagnosed with autism, the other "non-ASD affected". Participants were drawn from two samples, a Gothenburg catchment area sample and a "Stockholm Somali group" which have been previously used in a prevalence study of autism in Somali children in Sweden (see here). Those in the know about autism research will perhaps have heard about autism and Somali children a few times before (see here).
• Participants were coded according to ethnicity into one of three groups: Swedish, Miscellaneous (non-Scandinavian Europe, South America and East Asia) and African/Middle East. This was due to: "well-known ethnic disparity of vitamin D status."
• Results: "Children to parents of non-Scandinavian ethnicities had lower mean 25(OH)D levels than children to Swedish parents." See the previous point. 
• "The mean 25(OH)D level was lower in children with ASD... than in their siblings." This trend was significant in "the Swedish and Miscellaneous groups, but not in the African/Middle East group." The authors report that season of birth, a potentially important factor in birth vitamin D levels was likely not the primary variable to account for the ASD - non-ASD sibling differences but there were some disparities noted. I would also draw your attention to another comment from the authors: "Since we studied newborn children before diagnosis, our results are definitely unrelated to lifestyle and diet of the individual, although the mother’s lifestyle and other environmental factors cannot be ruled out."
• Author conclusion: their findings may support: "the hypothesis that developmental vitamin D deficiency during late pregnancy may carry an increased risk of ASD in the child." Alongside, that is, the requirement for further research with larger numbers of participants.

I would certainly echo the sentiments of the authors for the need for larger-scales studies of any connection between low pregnancy/birth vitamin D levels and risk of autism. This is however not the first time that this issue has been studied as per my commentary on the results from Whitehouse and colleagues [3] (see here) who based on the use of the Autism-Spectrum Quotient (AQ) (itself the topic of some recent inquiry) concluded that: "Maternal 25(OH)-vitamin D concentrations were unrelated to offspring scores on the majority of scales" bearing in mind their focus on mums not offspring when assaying for vitamin D.

A few further points before I let you go about your business.

"In this study we did not examine other possible causes for ASD, such as for instance infections during pregnancy." A very important point indeed if one looks at some of the research literature in this area (see here).

"Autoimmunity is another possible cause for ASD, which was not investigated. However, as low vitamin D is suggested to contribute to the pathogenesis of autoimmunity... our findings could be relevant in this context as well." Again, another potentially important point raised here on the basis of other research which has brought the issue of autoimmunity into the autism-vitamin D frame (see here). More generally, the issue of autoimmunity and autism is of increasing research interest.

Finally, the authors leave us with a tantalising question: "whether or not adequate supplementation of vitamin D to pregnant women might lower the risk for ASD in the offspring"? Before anyone get's ahead of themselves, I think we need quite a bit more discussion and study on this question specific to autism given that more generally vitamin D for pregnant women is seemingly being more frequently indicated.

Just one more thing (to coin a phrase)... although no-one really knows the specific hows, whys and wherefores of any vitamin D connection to autism, I'd be minded to suggest that physiological issues such as gut permeability (yes, it is a real thing) might also register on any future research endeavours given data like that from Assa and colleagues [4] adding to an already interesting area (see here). I'm not saying that this is the only potential factor but one among many.

Music: Do you feel lucky punk?

----------

[1] Fernell E. et al. Autism spectrum disorder and low vitamin D at birth: a sibling control study. Molecular Autism. 2015; 6: 3.

[2] Kočovská E. et al. Vitamin D in the General Population of Young Adults with Autism in the Faroe Islands. J Autism Dev Disord. 2014 Jun 14.

[3] Whitehouse AJ. et al. Maternal vitamin D levels and the autism phenotype among offspring. J Autism Dev Disord. 2013 Jul;43(7):1495-504.

[4] Assa A. et al. Vitamin D Deficiency Predisposes to Adherent-invasive Escherichia coli-induced Barrier Dysfunction and Experimental Colonic Injury. Inflamm Bowel Dis. 2015 Jan 14.

----------

Elisabeth Fernell, Susanne Bejerot, Joakim Westerlund, Carmela Miniscalco, Henry Simila, Darryl Eyles, Christopher Gillberg, & Mats B Humble (2015). Autism spectrum disorder and low vitamin D at birth: a sibling control study. Molecular Autism : 10.1186/2040-2392-6-3

Finland, parental migration and offspring Asperger syndrome

A quote from the paper by Venla Lehti and colleagues [1] to start things off: "The study showed that children whose parents are both immigrants have a significantly lower likelihood of being diagnosed with Asperger's syndrome than those with two Finnish parents."

Can I cook, or can't I?

Based on an analysis of data derived from "the Finnish Hospital Discharge Register" and "the Finnish Medical Birth Register", researchers looked at the records of children with a diagnosis of Asperger syndrome (AS) born between 1987-2005 (n=1783) to ascertain "maternal and paternal immigration" status including mother language spoken. Compared with over 7000 control participants they found that there was indeed something significant to see when it came to parental origins and in particular when mothers and/or fathers were "born in Sub-Saharan Africa".

This is intriguing data. The fact that authors looked at the diagnosis of AS and, by diagnostic criteria, those positioned at a specific point on the autism spectrum with symptoms not normally accompanied by the presence of learning disability (intellectual disability) and fewer issues with spoken language, is important. Previous research by this same group [2] also discussed on this blog (see here) had indicated that "the risk of childhood autism was increased for those whose parents are both immigrants" compared to having two Finnish parents based on the same data registries. The contrast with the more recent data reporting that parental migration status might be protective against receipt of a diagnosis of AS compared with non-immigration status is stark.

That being said, we have seen other hints that when an offspring diagnosis on the autism spectrum is received where parents are immigrants from certain parts of the world to certain other parts of the world, there is a greater tendency towards autism plus learning disability to be present. I've covered it a few times on this blog (see here for example based on data from Sweden). The chatter a while back about the Somali population living in Minneapolis also came to something of a similar conclusion (see here).

The growing idea that autism might be better reflected as a plural condition - 'the autisms' - over and above the singular definition currently being applied to cover some significant heterogeneity across presentation, potentially receives some valuable support from research such as this. Obviously, one has to tread carefully if and when labelling a type of autism potentially linked to something like immigrant status so as not to stereotype or fuel some viewpoints. That being said, there are perhaps quite a few studies to do comparing autism in immigrant children vs. non-immigrant autism presentation which might yet provide some valuable information to autism research in general.

Music then: Taylor Swift - We Are Never Ever Getting Back Together. Although another band did talk about something similar a few years earlier: Beautiful South - A Little Time (and with a much better video).

----------

[1] Lehti V. et al. Parental migration and Asperger's syndrome. Eur Child Adolesc Psychiatry. 2014 Nov 8.

[2] Lehti V. et al. The risk of childhood autism among second-generation migrants in Finland: a case-control study. BMC Pediatr. 2013 Oct 19;13:171.

----------

Lehti V, Cheslack-Postava K, Gissler M, Hinkka-Yli-Salomäki S, Brown AS, & Sourander A (2014). Parental migration and Asperger's syndrome. European child & adolescent psychiatry PMID: 25381114

Increased rate of offspring autism among migrants

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

Autism and migration: new clues?

Autism in the Somali population, particularly the migrating Somali population, has been the topic of some debate down the years. I think back to the 2010 study by Barnevik-Olsson and colleagues* detailing an autism prevalence in Somalis living in Sweden of 0.98% compared with 0.21% in children of non-Somali origin alongside other factors related to vitamin D for example. OK, the vitamin D link is still speculative but the migratory aspect remains an interesting association. Enter a new study into the debate from Magnusson and colleagues** detailing some population based findings relating to parental migration status and risk of autism spectrum condition.

The summary:

• Based on an analysis of various records for the total child population of Stockholm County, Sweden (N=589,114) between 2001 and 2007, children with autism defined as high- and low-functioning were identified. I know some people don't like the terms 'high' and 'low' functioning as descriptors of autism, but in this case the authors were referring to cases where intellectual disability was or was not present.
• A total of 4952 cases of autism were identified; 2097 cases comorbid with learning disability (42%) and 2855 cases of autism without (58%). These splits are roughly in line with other data such as that reviewed by O'Brien and Pearson***.  
• When looking at children of migrant parents, there was an increased risk of having a child with autism and learning disability (OR = 1.5) and this risk was particularly pronounced for those migrating from countries with a low human development index and for children whose mothers migrated just before or during pregnancy (OR = 2.3).
• When it came to risk of having a child with autism without intellectual disability, there was actually a decreased risk for migrant mothers compared to children born to indigenous mothers. Whether this was a true reflection of risk or due to the fact that immigrant families might be less likely to seek child development services is unknown.
• These results were not explained by socio-economic, age or obstetric factors.

There are quite a few potentially important implications from this work which require comment.

Over 40% of cases of autism identified in this study were diagnoses of autism and learning disability. One of the blogs I like to follow is Harold Doherty's blog. Some of his more recent discussions have surrounded what will happen to those cases of autism and learning disability in the proposed revisions to the DSM criteria for autism. With the current figures in mind, the question has to be asked whether this kind of relationship will be picked up in any future studies if and when the new guidance is enshrined in diagnostic law.

One also needs to comment on the environmental implications from this latest study. The fact that risk of offspring with autism was elevated just before or during pregnancy implies that genes alone cannot guide this association. I say cannot guide this association but possibly they could if one was to assume that some epigenetic relationship may be evident. I think again back to the prenatal vits and SNPs study on autism from last year. So, assuming that mum is migrating from a warm, sunny environment to a cold, not so sunny (at least not with as strong a sun) environment, where the food may be different, the external environment different (including the 'chemical' environment) and the associated 'stress' that comes with moving to a different part of the world. Mmm.. seems to me that there are plenty of factors ripe for further study there.

Ultimately this is another study of population association and one has to bear in mind the limitations in terms of what information that can bring. Having said that, on top of the other immigrant studies undertaken on autism, there is a growing argument that more focused investigation might yield some interesting clues as to risk and potentially aetiology at least in some cases of autism.

* Barnevik-Olsson M. et al. Prevalence of autism in children of Somali origin living in Stockholm: brief report of an at-risk population. Developmental Medicine & Child Neurology. 2010; 52: 1167-1168

** 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

*** O'Brien G. & Pearson J. Autism and learning disability. Autism. 2004; 8: 125-140.
DOI: 10.1177/1362361304042718

Epidemiology of autism: contrasting differences

One of the more animated debates in autism research relates to the possible reasons behind the quite staggering increase in cases being diagnosed world-wide over the past 25 years or so. One of the benchmark studies used for prevalence of autism (note prevalence not incidence), at least in the UK, is the study published by Gillie Baird and colleagues back in 2006 suggesting a total prevalence of all autism spectrum conditions of 116.1 per 10,000.

Two recent reports caught my eye. The first was a comparison of autism prevalence rates in Denmark and Western Australia published by Parner and colleagues. As per the link they reported differences between Danish and Australian prevalence rates of total autism spectrum conditions (68 vs. 51 per 10,000 respectively). These rates are different. Not only between the two countries in question, but also compared with the Baird data. One could perhaps suggest that there were differences in the birth years covered or methodologies employed to "find" and "record" cases (whether it was actively searching for cases of merely reliant on database figures as much of the Danish data tends to be for example because of the way their healthcare records are set up). This could perhaps explain some difference; my question however would be how much can it explain? Does this mean that prevalence of autism spectrum conditions is higher in the UK, than in Denmark or Western Australia? If so, what are the factors influencing such a difference?

A second study that deserves some comment is a follow-up study from Barnevik-Olsson and colleagues on the prevalence of autism in Somali children living in Sweden born between 1999-2003. They reported prevalence of autism as a percentage comparing Somali children with non-Somali children (rates were 0.98% vs. 0.21% respectively). Their initial study published in 2008 showed rates of: 0.7% vs. 0.19% (Somali vs. non-Somali) for children born between 1988-1998. These data again show differences. Differences in the rates between Somali and non-Somali children with autism, differences between the birth years and also differences with the other studies listed in this post. The issue of whether autism rates are elevated in Somali children is the focus of some interest already so I am not going to speculate on any reasons why there may be a difference.

Going back to the Baird data, again with all the caveats regarding case ascertainment et al, are we actually saying that the prevalence of cases of autism spectrum conditions in Sweden (amongst non-Somali children) are so markedly different from the UK data? Questions, questions, questions.