KMT2B and nervous system disorder: Genetic confirmation of both POLG2- and KMT2B-related neurological diseases in P5 enabled disease specific interventions such as globus pallidus internus deep brain stimulation and mitochondriopathy-related anesthetic consideration at age 21 years, resulting in significant improvement of motor function and disability, similar to previously reported efficacy of deep brain stimulation in KMT2B-related dystonia [28].