Valbenazine Treatment of Tardive Dyskinesia in Adults With Intellectual/Developmental Disabilities

The goal of this open-label clinical trial is to test the safety and efficacy of valbenazine treatment in patients with Intellectual/Developmental Disability (IDD) who have a diagnosis of Tardive dyskinesia (TD). The main questions this study aims to answer are: * Does valbenazine treatment of TD in the previously untreated patient population of adults with IDD produce comparable amelioration of signs of movement disorder as what has historically been reported in adults without IDD? * Is valbenazine treatment of TD in persons with IDD as safe as what has historically been reported in adults without IDD? * Does valbenazine treatment improve Quality of Life (QOL) in persons with IDD and TD treated with valbenazine? * Does valbenazine treatment produce positive change in Activities of Daily Living (ADLs) in persons with IDD and TD? * Does valbenazine treatment of TD in persons with IDD reduce caregiver burden? In this study, 25 participants with IDD and TD will undergo valbenazine treatment for 24 weeks. The participants will be seen for a total of 5 visits: at baseline, and at follow up visits at 3 weeks, 6 weeks, 12 weeks, and 24 weeks. This study does not include a comparison group. Therefore, researchers will compare the response of the study participants to valbenazine treatment with those from a previous reported work that resulted in the FDA approval of this medication.