Tuesday, 1 May 2012

Autism and saliva

This is a little bit of an unusual post in that I want to discuss some of the collected data looking at a bit of a forgotten biological fluid, saliva, specifically with autism spectrum conditions in mind. The idea for doing this post stemmed in part from a quite recent paper by Soukup and colleagues* (full-text) which suggested that monitoring salivary uric acid might be a good idea in terms of cardiometabolic risk. Exactly how this finding itself might translate to some work on purines and autism linked to uric acid is food for thought.

Whilst pretty essential for lots of things, saliva or spit is not exactly dinner table conversation so I promise to try and keep this scientific. I hasten to add that I am not covering things like the excessive production of saliva (and onward things like drooling) or anything like that, accepting that such issues have been reported primarily as a side-effect to certain medications.

Certain areas on the autism research landscape have examined saliva as a functional biofluid. So looking at levels of cortisol in saliva is a bit of a favourite, as is some interest in salivary testosterone levels. A very recent paper by Rai and colleagues suggested that salivary antioxidant levels in autism were significantly reduced compared to asymptomatic controls which might tie in with some other findings on important markers of antioxidant health. Molecular biologists out there will already know about the value of buccal (cheek) samples as a way of collecting DNA but cheek cells are slightly different from plain old saliva.

The study I want to focus on is this one from Castagnola and colleagues** published in 2008. They reported results for a group of children diagnosed with an autism spectrum condition (n=27) compared to controls (n=23) based on a chemical analysis of naturally occurring salivary peptides. With my metabolomics hat on, this kind of study makes so much sense. Here you have a biofluid which most people produce in pretty copious amounts (during waking hours), easily available and relatively non-invasive to capture which contrasts against other research on blood as an analyte medium for example. The technology nowadays is such that you can get a lot of information from a spit sample.

Evidence suggests that little if any difference is present in the basic salivary parameters between people with autism and asymptomatic controls. The results produced by Castagnola, based on mass spectrometric analysis, suggested that hypo-phosphorylation (reduced) of certain salivary peptides was more common in the samples from children with autism compared to controls. Phosphorylation means the addition of a phosphate group to a molecule which can have various effects on a compound and its actions. The authors speculated that such hypo-phosphorylation might be a marker for other issues with phosphorylation in other tissues, using Rett syndrome as an example. Interestingly, they also draw a comparison with some of their other work on phosphorylation in preterm and term babies, suggesting that delayed peptide phosphorylation in the early days ".. may cause asynchrony or timing deregulation in some process involved in neuronal maturation, development or differentiation resulting in ASD phenotype". A few ideas there to digest possibly.

I'd like to think that as the technology gets more sensitive, analysis of saliva might be a growth area for at least some parameters related to autism currently only measurable via invasive collection of blood and plasma. Let's face it children in particular don't like having blood drawn, and children with autism are no exception to that rule. I note that studies have already reported in the area of vitamin D - measuring salivary 25-hydroxyvitamin D(3), for example; vitamin D having cropped up more than once in relation to autism. One wonders how many more biological parameters might also be measurable from a humble sample of spit.

To finish, how about a red hot chilli pepper to get us all salivating?

* Soukup M. et al. Salivary uric acid as a noninvasive biomarker of metabolic syndrome. Diabetology & Metabolic Syndrome. April 2012.
DOI: 10.1186/1758-5996-4-14

** Castagnola M. et al. Hypo-phosphorylation of salivary peptidome as a clue to the molecular pathogenesis of autism spectrum disorders. Journal of Proteome Research. 2008; 7: 5237-5232.