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Table S1. Concomitant medications of participants with fragile X syndrome from the Institute for Neurodegenerative Disorders. Table S2. Demographic and clinical characteristics of participants from the Institute for Neurodegenerative Disorders (IND). All participant are non-Hispanic. Table S3. Demographic and clinical data of participants from Johns Hopkins University (JHU). Table S4. Genetic and psychological assessments of participants from the Institute for Neurodegenerative Disorders. Table S5. Genetic and psychological assessments of participants with fragile X syndrome and family members from Johns Hopkins University. Table S6. Positron emission tomography (PET) data and analyses for participants from the Institute for Neurodegenerative Disorders. Table S7. Positron Emission Tomography (PET) data and analysis of participants from Johns Hopkins University. The authors thank Flora Tassone, Ph.D., Department of Biochemistry and Molecular Medicine, School of Medicine, UC Davis Health, Sacramento, California, for providing genetic and protein data about participants.

This research was made possible by a Radiology BRidge/Development Funding Initiative to STimulate and Advance Research (RAD BriteStar Bridge) Award from the Johns Hopkins University School of Medicine, Baltimore, Maryland, to JRB; the Intellectual & Developmental Disabilities Research Center (U54 HD079123), Kennedy Krieger Institute, Johns Hopkins Medical Institutions. Baltimore, Maryland, to JRB; and the Johns Hopkins Institute for Clinical and Translational Research (ICTR), Johns Hopkins University School of Medicine, Baltimore, Maryland, to JRB, which is funded in part by Grant Number UL1 TR003098 from the National Center for Advancing Translational Sciences (NCATS) a component of the National Institutes of Health (NIH), and NIH Roadmap for Medical Research. Its contents are solely the responsibility of the authors and do not necessarily represent the official view of the Johns Hopkins ICTR, NCATS or NIH.