Sensory reactivity difficulties can be challenging for children with autism spectrum disorder and their families, making everyday activities, such as a trip to the supermarket, an impossible task. This project will look at how children with single gene and idiopathic (meaning unknown origin) forms of ASD react to sensory stimuli, e.g. touch and sound. Sensory reactivity will be measured using parent reports, observations and physiological measures, such as heart rate. Our aim is to identify the most robust ways to measure sensory reactivity in children with ASD, which can be used to guide diagnosis (sensory over-reactivity and under-reactivity as proposed for DSM-5) and sensory-based treatments. In addition, by including children with single gene forms of ASD this research can help to identify potential biomarkers for sensory over-and-under-reactivity. This research will also help to better understand the sensory world of children with ASD and can be used to design sensory-friendly environments.