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Chapter 8214and contributors.77-79 Brain imaging studies, such as done by the ENIGMA working groups for copy number variants,80 mouse models and (stem)cell studies may be used to better understand the pathophysiology of conditions associated with GNDs over the life span or to identify new treatment targets.79, 81-83 An example can be found in a study that made use of mouse models of Fragile X syndrome, Rett syndrome and Down syndrome in addition to cell cultures to demonstrate that astrocytes contribute to the abnormal neural development found in these GNDs,78thereby providing insights into shared underlying mechanisms. Although individually rare, GNDs are collectively common affecting about 3% of the population,84 and inclusion or identification of individuals with GNDs in population-based prospective cohort studies, such as Lifelines DEEP or the Maastricht study,85, 86 may facilitate the study of the pathophysiology and biomarkers for disease by, for example, studies of the metabolome or microbiome,87, 88 and comparison between GNDs and with the general population. These large population-based studies often use standardized measurements and extensive phenotyping, in addition to assessment of genetic and environmental factors of all participants, which is not always feasible in smaller studies of individual GNDs. Last, improvement and study of the use of wearables and applications, such as used for experience sampling, may help to understand the effects of stress, nutrition or physical exercise on physical and mental health in GNDs, and can be used to study effects of interventions aimed at improving healthy living and aging. Experience sampling has already been applied in individuals with 22q11.2DS in the study of cortisol reactivity to subjective stress, demonstrating altered cortisol response to daily stress in individuals with 22q11.2DS compared to controls.21 This may aid in our understanding of conditions such as post-traumatic stress in adults with 22q11.2DS (chapter 7), and other physical symptoms that may be related to stress. Actigraphy may be used to study the effect of sleep interventions, which has been done in children with Down syndrome,89 and may be used to study sleep disorders and interventions in other GNDs as well, including obstructive sleep apnea in adults with 22q11.2DS (chapter 4).