Gastroparesis (GP) in children and adults is characterized by delayed gastric emptying in the absence of mechanical obstruction. GP is associated with significant morbidity and mortality yet little is known regarding its incidence, prevalence, and natural history in children. This knowledge gap in pediatric GP is exacerbated by the overlap in symptoms and pathophysiology with functional dyspepsia (FD), a common disorder in adults and children. The limited data suggests significant differences between clinical symptoms and pathophysiology of GP and FD in children vs adults. Thus, data regarding GP and FD in adults is unlikely to provide insight and fill the knowledge gaps regarding GP and FD in children. These issues (among others) underscore need for childhood GP- and FD-specific research strategies. Thus, the goals of this renewal application are to build on and extend our previous Pediatric Registry work as part of the NIDDK Gastroparesis Consortium (GpCRC) (e.g., recruitment into the Registry, development of a pediatric Quality of Life and Symptom GP Module; PedsQL/Symptom GP Module), ultimately, to determine the factors contributing to disease severity measured by quality of life and symptoms. Our Specific Aims are: Aim 1 – Complete validation of the PedsQL/Symptom GP Module via field testing and develop an analogous module for pediatric FD using qualitative measures followed by field testing. Aim 2- Determine the role of the following potential contributors to disease severity in pediatric GP and FD: 2a - Pathophysiologic: a) Visceral hypersensitivity (via water load satiety testing); b) Gastric accommodation (via intragastric meal distribution); c) Gastric emptying rate (scintigraphy); d) Duodenal/gastric inflammation (mast cells and eosinophils); e) Gastric/proximal gut barrier function (gut permeability). 2b - Psychosocial distress: Engage with psychologists to assess a) Somatization (Children’s Somatization Inventory); b) Depression (Children’s Depression Inventory) c) Anxiety (State-Trait Anxiety Inventory); d) Disability (Functional Disabilities Inventory); e) Catastrophizing (Pain Catastrophizing Scale). 2c - Dietary intolerances: Engage with dietitians, patients, and parents to determine self-identified food intolerances and eating behaviors in children with GP and FD. Aim 3 - To accomplish the above, expand Registry recruitment by including more pediatric centers, with some linked to adult GpCRC sites in order to begin to explore barriers to transition from pediatric to adult care. This innovative multidisciplinary approach will prospectively begin to fill the vast knowledge void regarding GP and FD in children. The current proposal is responsive to RFA-DK-20-504 by achieving among other goals, to: build on our previous gains, enlist expertise of psychologists and dietitians, expand recruitment sites, and study pediatric to adult care transition.