Enter then two further recent articles - one from Bradley Ferguson and colleagues  and one from María José Penzol and colleagues  - which further add to the evidence base in this area. Both papers are open-access, so please peruse at your leisure. The long-and-short of them can be quickly summarised:
- The Ferguson paper set out to examine the "relationships among GI [gastrointestinal] problems, problem behaviors, and internalizing symptoms in a sample of 340 children and adolescents with ASD [autism spectrum disorder]." Caregivers/parents reported on their child's GI issues. Bottom line: "The majority of the sample experienced constipation (65%)." Various other functional GI issues were also reported.
- The Penzol paper "reviewed the medical records of all patients admitted to the Comprehensive Medical Program for ASD (AMITEA) at Gregorio Marañón University General Hospital from January 2012 to December 2015." They analysed records for nearly 850 patients diagnosed with ASD. Their data were collected and transcribed by physicians including the "presence of fGID [functional gastrointestinal disorders] (gastrointestinal reflux, aerophagia, functional diarrhea, functional constipation, functional abdominal pain, cyclic vomiting)." Bottom line: "At least one fGID was present in 30.5% of patients, constipation being the most prevalent (47.4% of fGID patients)." They also observed that GI issues *seemed* to be related to the presence of intellectual (learning) disability, sleep issues and behavioural problems. These are not novel associations (see here and see here).
Of course there are strengths and weaknesses to those studies. No-one would dispute the fact that these are not perfect data. But, set within the context of a mountain of peer-reviewed science suggesting that something like constipation is over-represented when it comes to a diagnosis of autism, the collected results add a further layer of evidence. They also ask the question 'why', why oh why have we not got a greater handle on how to successfully treat/manage such symptoms?
 Ferguson BJ. et al. The Relationship Among Gastrointestinal Symptoms, Problem Behaviors, and Internalizing Symptoms in Children and Adolescents With Autism Spectrum Disorder. Front Psychiatry. 2019 Apr 9;10:194.
 Penzol MJ. et al. Functional Gastrointestinal Disease in Autism Spectrum Disorder: A Retrospective Descriptive Study in a Clinical Sample. Front Psychiatry. 2019 Apr 10;10:179.