Project Summary/Abstract The ongoing goal of the Autism Biomarkers Consortium for Clinical Trials (ABC-CT) is to establish electroencephalography (EEG) and eye-tracking (ET) biomarkers that can be used for stratification and/or as sensitive and reliable objective assays related to social function in autism spectrum disorder (ASD) clinical trials. This renewal application seeks to further validate promising measures through three studies designed to enhance and extend the original ABC-CT study: (1) a confirmation study of the original findings in a new cohort using similar design (T1: Baseline, T2: 6 weeks post baseline, T3: 24 weeks post baseline) and sample size/characteristics (200 with ASD, 200 with typical development (TD)); (2) a follow-up study of the original cohort (N=399) to re-administer the biomarker and clinical batteries 2.5-4 years after original ABC-CT enrollment; (3) a feasibility study of parallel EEG and ET biomarkers in preschool-aged (3-5-year-old) children (25 with ASD, 25 with TD). The biomarker and clinical batteries measure key facets of social-communication in ASD using well- validated paradigms appropriate for the intended developmental and cognitive range. The study will rely on the same leadership and five Collaborating Implementation Sites (“Sites”) from the first phase, all highly experienced in multi-site collaborative clinical research using the proposed clinical, EEG, and ET methodologies. The Data Coordinating Core (DCC) will provide a secure informatics infrastructure for communication and data integration across the consortium to ensure organized data management, quality control, and reliable upload to the National Database for Autism Research (NDAR) and NIH Data Repositories. The Data Acquisition and Analysis Core (DAAC) will oversee consistent use of scientific standards and methodological rigor for data acquisition, processing, and analytics. The Administrative Core, in coordination with federal partners in this cooperative agreement, will oversee the operations of the sites, DCC, and DAAC to ensure methodologically and ethically rigorous, efficient completion of study aims: 1) In the confirmation study with a new cohort, evaluate whether EEG and ET measures, individually or in combination, have utility as stratification biomarkers and/or sensitive, reliable measures of change in clinical trials; 2) In the follow-up study of the original ABC-CT cohort, assess long-term stability, sensitivity to change, and longitudinal predictive value of the markers; 3) In the feasibility study, determine the viability of parallel EEG and ET measures as potential biomarkers in 3-5-year-old children with ASD and TD. Blood (DNA) samples will be collected from participants with ASD and biological parents for future genomic analyses, and raw, processed, and analyzed data will be shared to create a community resource accessible for use by all qualified investigators. These objectives are designed to further develop promising biomarkers to advance qualification with the FDA Biomarker Qualification Program.