Baby teeth, metals and autism part 2

Consider this post on the findings reported by Paul Curtin and colleagues [1] which concluded that "altered zinc-copper rhythmicity precedes the emergence of ASD [autism spectrum disorder]" an extension of other previous discussions on this blog (see here). The research starting material was, once again, baby teeth, including teeth derived from an interesting initiative called "the Autism Tooth Fairy Project" based in Texas, USA.

On the last blogging occasion, the paper by Manish Arora and colleagues [2] was central to my discussions, and the use of some really interesting analytical technology to look at levels of various metals in tooth layers: Laser ablation-inductively coupled plasma mass spectrometry. Fast forward a year or so, and authors (including Arora) moved on to bigger and better things, this time focusing specifically on the metals zinc and copper "from the second trimester to approximately 1 year postnatally." Such a feat was achieved because baby teeth, much like the rings of a tree, provide a sort of 'album' of levels of such metals over a child's earliest years. Both these metals and their ratio also have some previous research 'form' when it comes to autism (see here).

"Our participants were recruited from four different studies being undertaken in three countries." Yep, so alongside teeth from the RATSS study initiative (aptly named the 'roots' of autism/ADHD study) forming a discovery dataset, authors also examined teeth gathered as part of other research initiatives including a favourite here in Blighty: the Avon Longitudinal Study of Parents and Children (ALSPAC). These non-RATSS teeth formed a replication set (to try and replicate the data found in the discovery set). Add in some nifty statistical analysis and set lasers to stun or should that be ablate...

Results: authors reported finding "strong evidence for abnormalities in zinc-copper cycles in ASD characterized by shorter duration, lower complexity, and less determinism." A quick translation: well, I'll be honest and tell you that I'm not exactly sure what that actually meant. I think it had something to do with the way the data were analysed, being "analogous to a spectrogram." Suffice to say that levels of copper and zinc were seemingly different in those diagnosed with autism compared with not-autism controls at different tooth time periods. When all this metal data was analysed using some statistics designed to try and 'classify' those with autism from those not-autistic, authors also noted zinc-copper cycles in teeth "allowed for a robust classification of ASD cases and controls." So: "Using optimal threshold criteria, this model was 90% accurate in predicting ASD cases, with 100% sensitivity for ASD diagnosis and 85% specificity to controls." Those stats aren't bad when one considers the importance of sensitivity and specificity to any classifying 'test'.

Although interesting, one has to bear in mind that this research was based on the use of baby teeth and their possible 'retrospective' association with autism. Nobody is advocating pulling out baby teeth as some sort of autism test! The focus on metals however, and specifically "measures of metal rhythmicity" provides some welcome information about how such 'rhythms' *might* show differences in relation to autism. This could reflect things like differing 'exposure' patterns or, more likely, some innate differences in the biological 'processing' of such metals. On that last point, this work potentially fits in with what is emerging in other independent data: metal (various metals) metabolism in the context of some autism seems to be 'unusual' (see here).

----------

[1] Curtin P. et al. Dynamical features in fetal and postnatal zinc-copper metabolic cycles predict the emergence of autism spectrum disorder. Science Advances. 2018. 30 May.

[2] Arora M. et al. Fetal and postnatal metal dysregulation in autism. Nat Commun. 2017 Jun 1;8:15493.

----------

On baby teeth, metals and autism

So: "using novel biomarkers of early life exposure, we observed differences in uptake of multiple toxic and essential elements over the second and third trimesters and early postnatal periods in MZ [monozygotic] and DZ [dizygotic] twins discordant for ASD [autism spectrum disorder]."

That was the conclusion reached in the paper by Manish Arora and colleagues [1] (open-access). Using baby teeth as a sort of 'biologic hard drive' according to the accompanying press release (see here), researchers observed some interesting differences across twin groups with or without a diagnosis of ASD according to various pre- and post-natal periods. In particular they noted that: "In ASD cases, higher lead levels were observed over the prenatal period and first 5 months postnatally" and: "Zinc levels were lower in cases during the third trimester."

This paper has already received quite a lot of media attention (see here for example). Thankfully, many of the media outlets have focused on some of the quite important details when it comes to the study; namely that the total number of participants was quite small overall, despite being drawn from a larger research initiative: the Roots of Autism and ADHD Twin Study in Sweden (RATSS).

I am however very interested in both the methods employed during the Arora study and the results obtained. Baby teeth as a focus of autism research? I've speculated on that before (see here). The use of "Laser ablation-inductively coupled plasma mass spectrometry" is also rather good to see; being a method of choice for the determination of metals in various samples (ICP mass spectrometry) coupled to the use of laser ablation to free up the dentine surface of baby teeth for said analysis.

The results talking about levels of lead (Pb) and zinc (Zn) are also not entirely novel in relation to the autism spectrum. On this blog I've talked before about other, independent research observing a possible relationship between lead exposure and autistic traits (see here) on the basis that lead is a known neurotoxin and seemingly serves no physiological function in the body. Zinc, typically reductions in zinc levels, are also not entirely unknown to the autism spectrum either (see here); where zinc is required for quite a few important biological reactions/processes [2].

What's missing from the Arora study? Well, without trying to 'rock the boat' or anything, the focus on lead, zinc and manganese is a little limited given that other types of metals have also been discussed in the context of autism (see here). Yes, I know to mention mercury in the same sentence as autism is high on the 'hot potato' scale but peer-reviewed science is peer-reviewed science (see here). I might also have liked to see how tooth levels of those metals also correlated with blood levels of metals in the context that exposure might not be the only issue when talking about atypical metal levels and autism (see here).

Still, this is a good initial effort and should hopefully pave the way for further investigations into how metal exposure and/or inadequacies can very much impact on behaviour and development.

----------

[1] Arora M. et al. Fetal and postnatal metal dysregulation in autism. Nat Commun. 2017 Jun 1;8:15493.

[2] Frassinetti S. et al. The role of zinc in life: a review. J Environ Pathol Toxicol Oncol. 2006;25(3):597-610.

----------

Arora M, Reichenberg A, Willfors C, Austin C, Gennings C, Berggren S, Lichtenstein P, Anckarsäter H, Tammimies K, & Bölte S (2017). Fetal and postnatal metal dysregulation in autism. Nature communications, 8 PMID: 28569757

Baby teeth and autism research

"This report provides evidence that teeth can be useful biomarkers of early life exposure for use in epidemiologic case-control studies seeking to identify differential unbiased exposures during development between those with and without specific disorders such as autism."

That was one of the conclusions reached in the paper by Raymond Palmer and colleagues [1] (open-access available here) who played science tooth fairy with 71 deciduous teeth (baby teeth) provided by children with autism from a "tooth repository consisting of 928 children’s deciduous teeth." As per other reports with autism in mind using these potentially important biological samples [2], there is quite a lot of information potentially available from baby teeth assuming one knows how to handle such samples.

For Palmer et al the analytical methods of choice were "liquid chromatography tandem mass spectrometry and gas chromatography" echoing other autism biomarker research discussed on this blog (see here) and fairly commonly appearing in the peer-reviewed literature [3]. Levels of various compounds were assessed in the pulverised baby teeth samples including "acetaminophen [paracetamol], ARA [arachidonic acid], DEET [diethyl-m-toluamide], TCPy [3,5,6-trichloro-2-pyridinol], IMPy [2-isopropyl-6-methyl-4-pyrimidinol], and MEHP [mono-2-ethylhexyl phthalate]." Just in case you aren't an organic chemist, many of those compounds are metabolites of "pesticides, plastics, or medications" and were studied in light of previous work from this authorship group [4] and the suggestion that some of them might be relevant to autism risk and/or onset (see here for example) or at least serving up an interesting correlation.

Consistent with that previous report, Palmer and colleagues "demonstrated that specific semivolatile organic chemicals relevant to autism etiology can be detected in deciduous teeth." Drawing on information from both US children with autism (a "collection of deciduous teeth through collaborative efforts with the Interactive Autism Network (IAN)") and Mexican children with autism, various results are presented. "Despite demographic differences in the two samples, there were similar rates of detection for all chemicals" was one of the primary findings. So, round about 40% of samples from both geographic groups were detected to have traces of acetaminophen (paracetamol) in them for example. This finding tallied to some degree with parent report about paracetamol use during pregnancy and infancy. Other results can be seen in some of the accompanying tables (see here for example).

Importantly, Palmer and colleagues discuss what their findings do and do not mean. "While we have demonstrated that chemicals relevant to ASD [autism spectrum disorders] can be detected in deciduous teeth and are associated with mothers’ self-reported exposures, our results are limited in generalizability—largely due to the sample consisting entirely of children with ASD." In other words, the sole focus on baby teeth from children with autism does not necessarily mean that any compounds detected 'cause' autism given the snapshot view of their study and the lack of appropriate asymptomatic control samples analysed. Further work is indicated in this area to "include more diverse participants and neurotypical children as controls will allow case/control comparisons."

The use of baby teeth represents an interesting addition to tissue analysis when it comes to autism. Given the availability of such teeth, the timing of their availability and the relatively non-invasive way that such samples can be collected, there are quite a few positives to the use of such as resource in autism research. Combined with other fairly non-invasively collected samples such as urine (see here), saliva samples (see here) and potentially even things like nail clippings [5], there is quite a bit of information potentially available for autism research. That being said, the word 'biomarker' with autism in mind, needs to be rather carefully used in light of things like plurality...

Music: Maroon 5 - Sugar.

----------

[1] Palmer RF. et al. Organic Compounds Detected in Deciduous Teeth: A Replication Study from Children with Autism in Two Samples. J Environ Public Health. 2015;2015:862414.

[2] Adams JB. et al. Mercury, lead, and zinc in baby teeth of children with autism versus controls. J Toxicol Environ Health A. 2007 Jun;70(12):1046-51.

[3] Wang H. et al. Potential serum biomarkers from a metabolomics study of autism. J Psychiatry Neurosci. 2015 Sep 22;40(5):140009.

[4] Camann DE. et al. Acetaminophen, pesticide, and diethylhexyl phthalate metabolites, anandamide, and fatty acids in deciduous molars: potential biomarkers of perinatal exposure. Journal of Exposure Science and Environmental Epidemiology. 2013; 23: 190–196.

[5] Shu I. et al. Detection of Drugs in Nails: Three Year Experience. J Anal Toxicol. 2015 Oct;39(8):624-8.

----------

Palmer, R., Heilbrun, L., Camann, D., Yau, A., Schultz, S., Elisco, V., Tapia, B., Garza, N., & Miller, C. (2015). Organic Compounds Detected in Deciduous Teeth: A Replication Study from Children with Autism in Two Samples Journal of Environmental and Public Health, 2015, 1-9 DOI: 10.1155/2015/862414