When trying to provide a simple description of what oxalate actually is, I am at a slight loss. I can provide you with quite a technical reference (here) showing a chemical structure, even complete with a ball and stick graphic but I don't think most people are really that interested in such an overview. This description is perhaps a little more user-friendly but still I am left slightly wanting.
Suffice to say that oxalate, a phytochemical, is a compound found in quite a few plants and vegetables (sometimes by another form, oxalic acid) and generally speaking does not seem to be a good thing to have too high a level of, particularly with its connection to kidney stones. There is quite a bit of history around oxalate and oxalic acid. I remember many years ago being told not to eat the leaves of the rhubarb plant because they were poisonous. So whilst rhubarb stalks are the primary component of perhaps the best ever dessert ever invented, rhubarb crumble, the leaves have been linked to some not-so-nice effects throughout history, with oxalic acid remaining a prime candidate.
Reading therefore a new paper by Konstantynowicz and colleagues (full-text)* including Susan Owens as part of the authorship team, that measured levels of urinary and plasma oxalate may be 2-3 times higher in children / teenagers with autism compared with non-autism controls is slightly worrisome news. I say worrisome but alongside their findings, the authors thankfully reported no greater evidence of the markers for problems with kidney stones to be present in their cohort. This is a relief given that the pain from passing kidney stones has been described as 'excruciating'. I cannot begin to imagine what this pain would be for a child if it has the ability to make grown men cry.
Susan Owens has long championed a role for oxalate in relation to some cases of autism as well as the possible usefulness of implementing a low oxalate diet. This document in addition to those previously mentioned gives about a good a description of any as to why oxalate may not be a good thing for autism (note that I am not providing any endorsement either way). The suggestion seems to revolve around values pointing either to a genetic predisposition to hyperoxalurias (endogenous synthesis perhaps) or potentially some issues with gut bacteria; various strains of the more 'beneficial' bacteria having been suggested to be involved in the safe disposal of oxalate. The latter explanation potentially tied to previous bacterial findings in cases of autism and the latest revelations from Brent Williams and colleagues. Interesting also that other gastrointestinal-related issues are also mentioned in the text of the article in question including inflammation, gut hyperpermeability and that old favourite sulphation.
As with the multitude of other findings related to autism spectrum conditions, the role of oxalate in autism is complicated. I do wonder about the 'calcium' connection with oxalate in view of how tightly it can bind to calcium ions and potentially 'drag' calcium away from various sites in the body - might it have some implications for bone health and beyond? The use of vitamin C is also another worry where oxalate levels may be high in light of some suggestion that supplementation might be a perpetuating factor for stone formation. Certainly in amongst all this, there is enough to suggest oxalate in relation to autism might be a 'watch this space' compound.
*Konstantynowicz J. et al. A potential pathogenic role of oxalate in autism. European Journal of Pediatric Neurology. September 2011.