INTRODUCTION: Variable expressivity is an emerging characteristic of KMT2B-related dystonia. However, it remains poorly understood whether variants reoccurring at specific sites of lysine-specific methlytransferase-2B (KMT2B) can drive intra- and interfamilial clinical heterogeneity. Our goal was to ascertain independent families with variants affecting residue Arg2565 of KMT2B. METHODS: Whole-exome/genome sequencing, multi-site recruitment, genotype-phenotype correlations, and DNA methylation episignature analysis were performed. RESULTS: We report four individuals from two families harboring the variant c.7693C > G, p.Arg2565Gly. In an additional patient, a de-novo c.7693C > T, p.Arg2565Cys variant was identified. The observed phenotypic spectrum ranged from childhood-onset dystonia (N = 2) over unspecific intellectual disability syndromes (N = 2) to undiagnosed behavioral symptoms in adulthood (N = 1). Samples bearing p.Arg2565Gly had a KMT2B-typical episignature, although the effect on methylation was less pronounced than in carriers of loss-of-function KMT2B variants. CONCLUSIONS: We established the existence of a KMT2B missense-mutation hotspot associated with varying degrees of disease severity and expression, providing information for patient counseling and elucidation of pathomechanisms.
FörderungenAgency for Health Research of the Czech Republic German Federal Ministry of Education and Research (BMBF, Bonn, Germany) Else Kroner-Fresenius-Stiftung Federal Ministry of Education and Research (BMBF) Free State of Bavaria under the Excellence Strategy of the Federal Government Lander Technical University of Munich-Institute German Research Foundation (DFG ) National Institute for Neurological Research, Czech Republic, Programme EXCELES European Union - Next Generation EU Charles University: Cooperatio Program in Neuroscience EJP RD