Title: Temperament and character as endophenotype in adults with autism spectrum disorders or attention deficit/hyperactivity disorder Authors: Sizoo, van der Gaag and van den Brink

Lay abstract: In addition to the social communication and behavioural difficulties used to diagnose autism spectrum disorder (ASD) many of these individuals have often been shown to have problems with sensory processing. One difference commonly reported is that people with ASD either experience less pain than people without ASD or no pain. The current article considers the evidence for and against people with ASD experiencing less pain than people without ASD. Two different types of research are discussed in this article: (1) where people with ASD directly say how much pain they feel, either in real life or when experiencing pain in a research study compared with people without ASD, and (2) differences between people with ASD and those without in their behaviours when in pain. Studies were classified as being self/parent report, clinical observations (i.e. based on reports of medical professionals), observations of responses to medical procedures (i.e. how people respond to injections), or experimental examination of pain (i.e. in a research study). When people with ASD, their parents, or professionals reported on pain, it was found that people with ASD reported less pain than people without. However, when people were observed under painful conditions (either in medical situations or in research studies) there were either no differences between the groups or the ASD group appeared to experience more pain. This review suggests that the evidence for people with ASD experiencing a different amount of pain to people without ASD is mixed and we cannot say that this is a consistent feature of ASD. More systematic research is needed to understand ASD individuals’ responses to pain.