This book covers both molecular and clinical aspects of Fragile X Syndrome (FXS) and premutation disorders so that new targeted treatments can be understood by clinicians and parents. It covers all premutation disorders including FXTAS, FXPOI and FXAND problems. The main focus is to help clinicians to give the best care possible to patients with FXS and to understand a multidisciplinary treatment approach. Underserved populations such as babies and toddlers with FXS and mothers with the full mutation are highlighted, including the treatments that can be beneficial to them. This book also discuss fragile X associated disorders as they impact the family whose proband has FXS. A highlight of this book is the international perspective on how different cultures deal with FXS and targeted treatments.