Here, we present the case of a 15-year-old Japanese girl with Dystonia 28, childhood-onset; DYT28 (MIM#606834) showing early-onset generalized progressive dystonia and status dystonicus. The patient was genetically undiagnosed and had not responded to various medications. By trio-based whole exome sequencing and in silico analyses, we identified a de novo heterozygous variant of KMT2B: NM_014727.2: c.7828C > T, p(Arg2610Cys). Globus pallidus internus deep brain stimulation (GPi-DBS) therapy was considered; however, the therapy could not be performed due to the patient\'s poor nutritional status and repeated infections. GPi-DBS is considered to be an effective treatment for patients with KMT2B mutations, and genetic diagnosis is important before progression to status dystonicus.