In previous posts I have discussed co-morbidity of autism and coeliac disease, and the fact that whilst such co-morbidity is comparatively rare (as far as we know!) it nevertheless exists. For those cases where a genuine diagnosis of coeliac disease has been made through serological testing (and biopsy), there is a scientifically justifiable reason to embark on a gluten-free diet with the hope of remediation of coeliac symptoms (abnormal functional bowel habits, weight loss, etc) and pathology (flattening of mucosal villi) and possibly autistic symptoms (see here).
For those cases where testing for coeliac disease shows a negative result, the problems in justifying use of a gluten-free diet (perhaps alongside a casein-free diet) increase. No coeliac disease, no problem with gluten - or is there?
A recent study published by Jessica Biesiekierski and colleagues reported on the potential effects of gluten to cause gastrointestinal symptoms without coeliac disease being involved. They reported on a so-called "non-celiac gluten intolerance" which seemed to hold for some of their patient group diagnosed with irritable bowel syndrome (IBS). This was a very well conducted trial, double-blind, randomised, placebo-controlled and including a re-challenge element (I only dream about such methodology as this!). The only problem is that they could not explain why the trial worked: not coeliac disease, not intestinal permeability, not inflammation - some speculation on the direct action of gluten peptides on humoral immune response, perhaps.
This is of course only one study. A study that does not mention autism in any way shape or form and looked principally at gastrointestinal problems (of which only a proportion of people with autism present). It would be a huge leap to infer similar results or mechanisms in some cases of autism, particularly where gut problems are co-morbid.
It does however gift us a possible idea for investigation and potentially another reason why some people with autism seem to show an effect from the introduction of a gluten-free diet in the absence of co-morbid coeliac disease. Slice of bread anyone?