So: "we have concluded that milk-derived opioid peptides and DPPIV [dipeptidyl peptidase-4 (DPPIV)] are potentially factors in determining the pathogenesis of autism."
That was the quite sweeping statement made in the paper published by Beata Jarmołowska and colleagues . It continues a quite a long running research topic in autism circles (see here and see here) on whether the chemical arrangement of certain dietary components *might* have an important biological effect on at least some people diagnosed as being on the autism spectrum.
The Jarmołowska paper is open-access so there is no real need for me to go over the suggested hows-and-whys of some diets being potentially related to (some) autism. If you need some further reading on the topic, I'll direct you to other posts on this blog where I've discussed this 'gluten and casein' issue (see here) and onward, my professional interest in it for quite a few years.
The aim of the Jarmołowska study was to determine "BCM7 [β-casomorphin-7] influence on DPPIV functioning in children with ASD in comparison to healthy children." 'Healthy children' is the term for the control group used by the authors by the way, not me. They "examined content and activity of serum DPPIV, content of BCM7 in serum and urine, and studied the effect of hydrolysed bovine milk, as a source of opioid peptides, on DPPIV gene expression in peripheral blood mononuclear cells (PBMC) in both groups."
Results: "We found that the content of BCM7 in serum was significantly higher (p < 0.0001) in ASD than in the control group." Urine concentrations of BCM7 were not significantly different among those with autism compared with controls. Also: "Concentration of DPPIV was found to also be significantly higher in serum from ASD children compared to the control group (p < 0.01)."That was about the sum of the differences noted by researchers.
Caveats? Well some. So: "ELISA test enabled identification of BCM7 contents in the serum and urine from patients, as well as in tested peptide extract obtained from hydrolyzed bovine milk." Authors do mention how the testing was carried out "in triplicate" following a previously published protocol. I don't dispute the results they got but am not exactly enamoured with the ELISA method used. I'd much rather see the analysis undertaken using something like mass spectrometry or similar technology, given the precision that comes with such methods (see here) based for example, on the use of internal standards. Perhaps if the authors still have their samples, they might consider further analyses if available to them?
Although researchers provide quite a bit of information about their participant groups, I also noted one important detail to be missing: were any of their participants - diagnosed with autism or not - following any special dietary regime? Y'know, they talk about casein (milk) free diets and how such diets are supported by "numerous scientific reports." So I guess in a cohort of 86 children diagnosed with autism, at least a few of them might be following such a dietary intervention? I've searched their paper but couldn't find anything to say that they were or weren't.
Putting such issues to one side, I don't want to take anything away from the Jarmołowska findings. As they end their paper: "this issue requires further investigation." I wouldn't disagree.
 Jarmołowska B. et al. Role of Milk-Derived Opioid Peptides and Proline Dipeptidyl Peptidase-4 in Autism Spectrum Disorders. Nutrients. 2019 Jan 4;11(1). pii: E87.