Nihr BioResource, F. Lucy Raymond, Shekeeb S. Mohammad, TD Graves, Susan J. Hayflick, Bert B.A. de Vries, Katy Barwick, Conor Fearon, Dora Steel, Mark Hallett, Asif Doja, Emilie Chan Seng, Camilo Toro, Fiona Stewart, Diane Demailly, Suh Young Jeong, Claudio M. de Gusmao, Frédérique Pavillard, Nutan Sharma, Fabienne Cyprien, Juan C Pallais, Brent L. Fogel, David R. FitzPatrick, Lucia Abela, Russell C. Dale, Bettina Balint, Natalie Trump, Michel Tchan, Sony Malhotra, Swasti Pal, Maya Topf, Manju A. Kurian, Michelle Sahagian, Julia Rankin, Laila Selim, Jeff L. Waugh, Sidney Krystal, Gustavo Polo, Caleb Rogers, Michel Mondain, Kailash P. Bhatia, Ishwar C. Verma, Marisela Dy-Hollins, Kelly A. Mills, Derek Wong, Laura Cif, William A. Gahl, Meredith W Allain, Sanaz Attaripour Isfahani, Agathe Roubertie, Jenny L. Wilson, Allison Gregory, Victoria Gonzalez, Carolyn D. Applegate, Nathalie Dorison, Jennifer A. Bassetti, Catherine Blanchet, Ada Hamosh, Deciphering Developmental Disorders Study, Hane Lee, Julien Baleine, Emma L. Baple, Gaetan Lesca, Anna Znaczko, Thomas Roujeau, Mario Sa, Laurence Lion François, Neil Mahant, Diane Doummar, Sandra Jansen, Marie Hully, Christine Coubes, Eva B. Forman, Victor S.C. Fung, Gaëtan Poulen, Raghda Zaitoun, Serena Galosi, Timothy Lynch, Xavier Vasques, Elise Schaefer, Richard Selway, Adeline Ngoh, Tuula Rinne, Philippe Coubes, Elizabeth L. Fieg, Rachel Fox, Jennifer Friedman, Andrea K. Petersen, Hugo Morales-Briceño, Rebecca Signer, Luis Rohena, Sandra Chantot Bastaraud, Chloé Laurencin, Kishore R. Kumar, Julian A. Martinez-Agosto, Ellyn Farrelly, Kathleen M. Gorman, Esther Meyer, Joel B. Krier, Ariane Soldatos, Lydie Burglen, Jean-Pierre Lin, Pierre-François Perrigault, Dolly Zhen, Harutomo Hasegawa, Mary D. King, Alba Sanchis-Juan, David A. Stevenson, Gilles Cambonie, Wui K. Chong, Christophe Milési, Vincent d'Hardemare, John R. Østergaard, Laboratoire de Recherche en Neurosciences Cliniques, IBM Systems Group, Service de Neurochirurgie [Montpellier], Centre Hospitalier Régional Universitaire [Montpellier] (CHRU Montpellier)-CHU Gui de Chauliac [Montpellier], Evelina London Children's Hospital, Institute of Child Health [London], University College of London [London] (UCL), Birkbeck College [University of London], Great Ormond Street Hospital for Children [London] (GOSH), Cambridge University Hospitals - NHS (CUH), University of Cambridge [UK] (CAM), Royal Devon and Exeter NHS Foundation Trust [UK], and Stanford University
Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5–37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden’s Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.