Autism spectrum disorder (ASD) is one of the most common neurodevelopmental disorders diagnosed in childhood, with a prevalence of 2% or higher. ASD presents along a spectrum, and characterization according to quantitative measures demonstrates continuous distribution of core traits extending into the general population. While both ASD diagnosis and ASD-related traits have been shown to be highly heritable, evidence also supports contributions of environmental risk factors, including prenatal exposure to air pollution and intake of certain nutrients. In order to address prior gaps in the understanding of environmental risk factors for autism, our team developed the Autism Spectrum Disorder Enriched Risk (ASD-ER) “cohort of cohorts.” In the first phase of ECHO, our cohort contributed to harmonization efforts of diet, air pollution, and neurodevelopment, and advanced use of abbreviated measures of the ASD-related phenotype, while capitalizing on the unique data for autism research presented by ECHO. Here, we propose to build off of these efforts while continuing follow-up of ASD-ER ECHO Phase-1 children through the critical and under-studied period of adolescence and early adulthood in the Trajectories and Environments in Autism: a Multi-cohort Study (TEAMS) project. The goals of this project are to: 1) Examine joint effects of early life air pollution exposure and diet on neurodevelopmental outcomes in ECHO-wide data, addressing the role that folate, fish/fatty acids, and other dietary factors may play in mitigating air pollution associations across neurodevelopmental diagnoses and their related quantitative traits (ASD, ID, and ADHD); 2) Evaluate multi-domain health trajectories of adolescents across neurodevelopmental outcomes in ECHO-wide data, and identify predictors of positive trajectories and outcomes. Using the unique longitudinal data collected through ECHO efforts, we will examine trajectories across mental and physical health and examine how these differ across neurodevelopmental diagnoses and traits. We will also seek to further characterize our specialized outcome area of neurodevelopment, and autism specifically, by conducting psychometric analyses of dimensional measures. Finally, we will 3) Maximize recruitment and retention of our cohort participants via implementation of the ECHO protocol. We will implement a unified recruitment and retention strategy facilitated by incentives and a network of support for adolescents with neurodevelopmental conditions, transition-age autistic youth, and their families. TEAMS will be the first longitudinal study of autistic younger sibling children followed from the womb to adulthood. In doing so, our project presents unique opportunities to advance understanding of environmental predictors and modifiers, conduct cross-outcome comparisons of neurodevelopmental disorders and their latent traits, characterize multi-domain trajectories and identify predictors of positive outcomes in autistic adolesce...