brain sciences Towards Mechanism- based Treatments for Fragile X Syndrome Edited by Daman Kumari and Inbal Gazy Printed Edition of the Special Issue Published in Brain Sciences www.mdpi.com/journal/brainsci Towards Mechanism-based Treatments for Fragile X Syndrome Towards Mechanism-based Treatments for Fragile X Syndrome Special Issue Editors Daman Kumari Inbal Gazy MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade Special Issue Editors Daman Kumari Inbal Gazy National Institute of Diabetes National Institute of Diabetes USA USA Editorial Office MDPI St. Alban-Anlage 66 4052 Basel, Switzerland This is a reprint of articles from the Special Issue published online in the open access journal Brain Sciences (ISSN 2076-3425) from 2018 to 2019 (available at: https://www.mdpi.com/journal/ brainsci/special issues/Fragile X Syndrome) For citation purposes, cite each article independently as indicated on the article page online and as indicated below: LastName, A.A.; LastName, B.B.; LastName, C.C. 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Contents About the Special Issue Editors ..................................... vii Daman Kumari and Inbal Gazy Towards Mechanism-Based Treatments for Fragile X Syndrome Reprinted from: Brain Sci. 2019, 9, 202, doi:10.3390/brainsci9080202 ................. 1 Daman Kumari, Inbal Gazy and Karen Usdin Pharmacological Reactivation of the Silenced FMR1 Gene as a Targeted Therapeutic Approach for Fragile X Syndrome Reprinted from: Brain Sci. 2019, 9, 39, doi:10.3390/brainsci9020039 .................. 6 Manar Abu Diab and Rachel Eiges The Contribution of Pluripotent Stem Cell (PSC)-Based Models to the Study of Fragile X Syndrome (FXS) Reprinted from: Brain Sci. 2019, 9, 42, doi:10.3390/brainsci9020042 .................. 24 David R. Hampson, Alexander W. M. Hooper and Yosuke Niibori The Application of Adeno-Associated Viral Vector Gene Therapy to the Treatment of Fragile X Syndrome Reprinted from: Brain Sci. 2019, 9, 32, doi:10.3390/brainsci9020032 .................. 43 Carolyn M. Yrigollen and Beverly L. Davidson CRISPR to the Rescue: Advances in Gene Editing for the FMR1 Gene Reprinted from: Brain Sci. 2019, 9, 17, doi:10.3390/brainsci9010017 .................. 58 Xiaonan Zhao, Inbal Gazy, Bruce Hayward, Elizabeth Pintado, Ye Hyun Hwang, Flora Tassone and Karen Usdin Repeat Instability in the Fragile X-Related Disorders: Lessons from a Mouse Model Reprinted from: Brain Sci. 2019, 9, 52, doi:10.3390/brainsci9030052 .................. 72 Rachel Michelle Sar´e, Christopher Figueroa, Abigail Lemons, Inna Loutaev and Carolyn Beebe Smith Comparative Behavioral Phenotypes of Fmr1 KO, Fxr2 Het, and Fmr1 KO/Fxr2 Het Mice Reprinted from: Brain Sci. 2019, 9, 13, doi:10.3390/brainsci9010013 .................. 87 Marwa Zafarullah and Flora Tassone Molecular Biomarkers in Fragile X Syndrome Reprinted from: Brain Sci. 2019, 9, 96, doi:10.3390/brainsci9050096 ..................101 Rakhi Pal and Aditi Bhattacharya Modelling Protein Synthesis as A Biomarker in Fragile X Syndrome Patient-Derived Cells Reprinted from: Brain Sci. 2019, 9, 59, doi:10.3390/brainsci9030059 ..................124 Craig A. Erickson, Walter E. Kaufmann, Dejan B. Budimirovic, Ave Lachiewicz, Barbara Haas-Givler, Robert M. Miller, Jayne Dixon Weber, Leonard Abbeduto, David Hessl, Randi J. Hagerman and Elizabeth Berry-Kravis Best Practices in Fragile X Syndrome Treatment Development Reprinted from: Brain Sci. 2018, 8, 224, doi:10.3390/brainsci8120224 .................136 v Jayne Dixon Weber, Elizabeth Smith, Elizabeth Berry-Kravis, Diego Cadavid, David Hessl and Craig Erickson Voice of People with Fragile X Syndrome and Their Families: Reports from a Survey on Treatment Priorities Reprinted from: Brain Sci. 2019, 9, 18, doi:10.3390/brainsci9020018 ..................145 Kristi L. Bartholomay, Cindy H. Lee, Jennifer L. Bruno, Amy A. Lightbody and Allan L. Reiss Closing the Gender Gap in Fragile X Syndrome: Review of Females with Fragile X Syndrome and Preliminary Research Findings Reprinted from: Brain Sci. 2019, 9, 11, doi:10.3390/brainsci9010011 ..................158 Debra L. Reisinger, Rebecca C. Shaffer, Ernest V. Pedapati, Kelli C. Dominick and Craig A. Erickson A Pilot Quantitative Evaluation of Early Life Language Development in Fragile X Syndrome Reprinted from: Brain Sci. 2019, 9, 27, doi:10.3390/brainsci9020027 ..................172 Lauren M. Schmitt, Rebecca C. Shaffer, David Hessl and Craig Erickson Executive Function in Fragile X Syndrome: A Systematic Review Reprinted from: Brain Sci. 2019, 9, 15, doi:10.3390/brainsci9010015 ..................184 Katherine C. Okoniewski, Anne C. Wheeler, Stacey Lee, Beth Boyea, Melissa Raspa, Jennifer L. Taylor and Donald B. Bailey Jr. Early Identification of Fragile X Syndrome through Expanded Newborn Screening Reprinted from: Brain Sci. 2019, 9, 4, doi:10.3390/brainsci9010004 ..................213 Anna W. Lee, Pamela Ventola, Dejan Budimirovic, Elizabeth Berry-Kravis and Jeannie Visootsak Clinical Development of Targeted Fragile X Syndrome Treatments: An Industry Perspective Reprinted from: Brain Sci. 2018, 8, 214, doi:10.3390/brainsci8120214 .................225 vi About the Special Issue Editors Daman Kumari is a Staff Scientist in the Laboratory of Cell and Molecular Biology at the National Institutes of Health. Dr. Kumari has made several important contributions to the understanding of repeat-mediated FMR1 gene silencing in FXS. Her current research is focused on developing treatment strategies for FXS that are based on FMR1 gene reactivation. Dr. Kumari serves on the Editorial Board of Genetic Testing and Molecular Biomarkers, Brain Sciences, and Journal of Autism and Developmental Research and is an ad hoc peer reviewer for many scientific journals. Inbal Gazy received her Ph.D. in Human Genetics from the Hebrew University of Jerusalem, Israel. She is currently a Postdoctoral Fellow in the Laboratory of Cell and Molecular Biology at the National Institutes of Health. Dr. Gazy has contributed to the understanding of molecular mechanisms that are responsible for several genetic diseases. Her recent work focuses on the molecular mechanisms and consequences of the unusual repeat expansion mutation responsible for fragile X-related disorders. vii brain sciences Editorial Towards Mechanism-Based Treatments for Fragile X Syndrome Daman Kumari * and Inbal Gazy Section on Gene Structure and Disease, Laboratory of Cell and Molecular Biology, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA * Correspondence: [email protected] Received: 13 August 2019; Accepted: 14 August 2019; Published: 16 August 2019 Fragile X syndrome (FXS) is the most common heritable form of intellectual disability, as well as the most common known monogenic cause of autism spectrum disorder (ASD), affecting 1 in 4000–8000 people worldwide. Almost 30 years ago, in 1991, the causative mutation for FXS was identified to be a CGG-repeat expansion in a gene named Fragile X Mental Retardation-1 (FMR1) located on the X chromosome [1,2]. At that time, it also became clear that methylation of a CpG island proximal to the repeats results in loss of gene expression and disease pathology [3–7]. While many decades have elapsed since these early discoveries, the underlying mechanisms involved in the expansion mutation, as well as the resulting gene silencing, still remain elusive. Soon after the identification of FMR1, a knockout mouse model was developed to better understand the role of FMR1 and its protein product, FMRP, in FXS [8]. Work from this mouse model, as well as other models, implicated FMRP activity in brain development, synaptic plasticity and neuronal transmission circuits [9,10]. This body of work led to clinical trials attempting to correct the deficient pathways in the brain of FXS patients [11]. However, all these clinical trials, although based on successful preclinical studies, did not show beneficial effects in FXS patients. Thus, currently there is no cure or effective treatment for FXS, and all the available interventions are focused on managing patient symptoms. Confronted with the gaps in knowledge and lack of treatments for FXS patients, the scientific community decided to revisit the approaches and practices used, implementing changes both in the preclinical and the clinical arenas. This special issue addresses some of the changes that are being made in the field towards finding effective treatments for FXS. As reviewed by Kumari et al. [12], there are two major avenues currently being pursued for development of effective treatments: (1) Targeting pathways altered in the absence of FMRP in the brain, and (2) Restoring FMRP expression. The fact that clinical trials focused on the restoration of altered pathways have not shown much promise to date, together with the development of new techniques and approaches in the biomedical field, has