Monday, 20 May 2013

Autism, plasma cytokines and siblings

I'm gonna try and be fairly brief in this post on the paper by Valerio Napolioni and colleagues* (open-access) looking at plasma cytokine profiles in cases of autism and their asymptomatic siblings. Brief because (a) the paper is open-access and (b) the participant groups (autism: n=25; sibling controls n=25) were relatively small so one has to be quite careful in extrapolating the findings with any large degree of confidence.
Siblings by Paul Klee @ WikiPaintings  

Just in case you are new to cytokines, we are talking biological signalling and communication, and in particular, the language of inflammation both pro- and anti-inflammatory (see this post).

With the autism spectrum conditions in mind, research into cytokines has filled quite a few peer-reviewed papers** from lots of different perspectives (see here and here for example). The main message so far is that it is complicated as per everything about autism and immune function.

Despite the quite small participant group, the Napolioni paper does seem to be an important paper for a few reasons:

  • They report no overall difference in cytokine profiles - measuring 40 cytokines - between cases of autism and their asymptomatic siblings. This despite the fact that autism symptoms and total IQ measures were different. That was the paper's headline.
  • But.... "the cytokine/chemokine levels in our subjects did correlate with the quantitative clinical traits"  or in other words, certain analysed parameters seemed to match with level of severity of autistic traits as measured by schedules such as VABS and SRS. "IL-1β appears to be the cytokine most involved in the quantitative traits".
  • When looking at the children with autism according to various clinical subgroups - non-verbal, functional gastrointestinal (GI) issues, history of regression, history of allergies - a few correlations were noted. So, children who were non-verbal seemed to show higher levels of cytokines such as IL-10, one of the more anti-inflammatory cytokines. Children with accompanying GI issues seemed to show higher levels of more pro-inflammatory cytokines like IL-1β and IL-6 compared with those without GI problems. Reported regression as part and parcel of symptom onset also seemed to show some correlation with specific cytokines too.

As the authors point out correlation does not imply causation. Such that just because they reported connections between cytokines and functioning and other factors does not necessarily mean that these observations are causative of autism (or anything else). That being said, as I hinted before, this is not the first time that cytokines and their connection to immune function have been discussed in the autism research literature (see yet another example of this here***); many correlations in similar directions makes for some interesting discussions at least.

That headline that children with autism and their siblings did not significantly differ in their cytokine profile carries a few possibilities for interpretation. The authors suggest that this could be evidence of "an ‘autism endophenotype’ that expands immune dysfunction to family members who are seemingly unaffected by the core symptoms of autism". One might also say the same thing about the Gondalia paper**** on gut bacteria in cases of autism and siblings (see here).

Assuming that the broader autism phenotype (BAP) does not come into play here, one might speculate that (a) cytokine profiles are not related to the presence of autism, or (b) that the manifestation of autism, some autism, is representative of cytokine involvement but in addition to other factors in terms of the affected sibling - "when an environmental stress (for example, prenatal exposure to environmental toxins, viral and bacterial infections, parental microchimerism, etc.) occurs during development". This last point takes me back to that 1971 John Money study on the appearance of familial autoimmune related conditions 'round about' the presence of autism and a similar correlation. Part of a predisposition to autism?

I note from Figure 4 of the paper, that when it came to summarising the various associations across the groups (and sub-groups), quite a few of the very significant differences seemed to be due to differences in IQ, which was tested using the Stanford-Binet Intelligence Scales (fifth edition). Aside from previous messages of caution on the use of this measure in autism research*****, one has to wonder whether this might be a more pertinent variable when it comes to cytokines and autism. I don't know enough about cytokine profiles in intellectual disability in children for example, to make any novel claims about this, but certainly intellectual development has been mentioned in the research literature with certain cytokines in mind******.

OK I said I would try and be brief with this post and have failed miserably. The Napolioni paper has though been worth it though for the potential insights that it might provide into the complex world of cytokines and immune function in relation to the presentation of autism.

To close, and following yet more 'we'll win it next year' commentary with regards to the UK entry in the event that is the Eurovision Song Content, might I suggest a group for your serious consideration as a contender next year?


* Napolioni V. et al. Plasma cytokine profiling in sibling pairs discordant for autism spectrum disorder. Journal of Neuroinflammation 2013; 10: 38.

** Goines PE. & Ashwood P. Cytokine dysregulation in autism spectrum disorders (ASD): Possible role of the environment. Neurotoxicol Teratol. 2013; 36: 67-81.

*** Ricci S. et al. Altered cytokine and BDNF levels in autism spectrum disorder. Neurotox Res. April 2013.

**** Gondalia SV. et al. Molecular characterisation of gastrointestinal microbiota of children with autism (with and without gastrointestinal dysfunction) and their neurotypical siblings. Autism Research. 2012; 5: 419-427.

***** Coolican J. et al. Brief report: data on the Stanford-Binet Intelligence Scales (5th ed.) in children with autism spectrum disorder. J Autism Dev Disord. 2008; 38: 190-197.

****** von Ehrenstein OS. et al. Child intellectual development in relation to cytokine levels in umbilical cord blood. Am J Epidemiol. 2012; 175: 1191-1199. 

---------- Napolioni V, Ober-Reynolds B, Szelinger S, Corneveaux JJ, Pawlowski T, Ober-Reynolds S, Kirwan J, Persico AM, Melmed RD, Craig DW, Smith CJ, & Huentelman MJ (2013). Plasma cytokine profiling in sibling pairs discordant for autism spectrum disorder. Journal of neuroinflammation, 10 PMID: 23497090