GI issues (medical) and ASD behaviors are strongly linked for most on the spectrum. The behavior of encopresis may stem from a medically treatable GI issue and this medical issue may in turn be contributing to "Aspie-ness" behavior. Mainstream GI Dr.s vary on their awareness of the strong association between the Gut-Brain connection and how it feeds into ASD. I recommend you find a reputable DAN! Dr (Medical Dr who has been through autism-related health training) to discuss what may be behind the encopresis as well as wether it may be linked to Aspie behaviors. If you get your son's gut to a more normal or healthy state, your son's need/fear to withold and some of the sensory issues may both improve. Some of the items that a DAN! Dr may evaluate are your son's pancreatic function (enzyme production for digestion) presence/level of secretory IgA, degree of good vs unfriendly flora including candida overgrowth, dietary stressors(food sensitivities and allergies). He/She may have specific recommendations for nutrition and dietary support. Most of these Drs will advise AGAINST regular Miralax treatment--only if immediately necessary--due to the potential for toxicity from the polyethylene glycol which is of extreme concern in patients who have leaky guts where it appears this large molecule is able to breach the gut and enter the body. Further, Mirolax is a bandaid, and does nothing to address what may be causing the constipation. While you don't mention whether you have tried this, I am just putting that out there because it seems for some Dr's, the "new normal" is for many kids to be constipated and require regular Mirolax --a subset of these kids may be harmed by regular use and for the majority who suffer no side effects, well, none will be cured until the conditions that are causing it fade or resolve. On the rare occasions where my son appears constipated and in need of "help" (during which time his ASD behaviors are generally worse), I use Magnesium Citrate to loosen his stool. My son generally has the opposite problem of frequent very loose stools . His gut has improved dramatically with diet, pancreatic enzymes with his food, probiotics, a diet rich if frest vegetables and fruits, and avoiding his inflammatory food triggers although he continues to have recurrences where perhaps food infractions or unfriendly flora get the upper hand. HTH, B.