Background/objectives: KMT2B-related dystonia (DYT28, OMIM #617284) is a progressive neurological condition characterized by early onset movement disorders with autosomal dominant inheritance. In this study, we describe the use of a genome methylation episignature methodology to functionally validate two variants of uncertain significance (VUS) in the KMT2B gene.
Methods: Genome-wide methylation status was assessed using the EPIC methylation assay in peripheral blood samples from two subjects with early onset movement disorder and missense variants of uncertain significance in the KMT2B gene (p.Leu1720Phe and p.Tyr2515Cys). After QC and normalization steps, we compared the M values for all 144 probes, previously described as an EpiSign for KMT2B-related dystonia, between the two subjects and 14 controls individuals.
Results: The individual harboring the p.Tyr2515Cys variant exhibited a hypermethylation profile compatible with pathogenic/likely pathogenic variants in KMT2B, allowing for variant reclassification, conclusive genetic counseling, and patient stratification for deep brain stimulation. In contrast, the individual harboring the p.Leu1720Phe variant had a methylation status similar to controls, practically ruling out KMT2B-related dystonia.
Conclusion: Investigation of methylation status can be a powerful tool to determine pathogenicity when facing KMT2B variants of uncertain significance. Methylation results may optimize genetic counseling and positively impact patient care.
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Methylation assay in KMT2B-related dystonia: a novel diagnostic validation tool.
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Department of Neurology, Beijing Children's Hospital, Capital Medical University, National Center for Children's Health, Beijing, China; Laboratory for Clinical Medicine, Capital Medical University, China. Electronic address:
Article Synopsis
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Universidad Militar Nueva Granada, Bogotá, Colombia.
Introduction: KMT2B-related dystonia is a childhood-onset movement disorder characterized by focal dystonia of the lower extremities progressing to generalized dystonia with predominant cervical, cranial, and laryngeal involvement. So far, fewer than 100 variants have been reported, the vast majority being de novo mutations. The presenting frame of KMT2B dystonia, with dysmorphology features and other complex neurologic symptoms shows the spectrum of KMT2B dystonia as a probable syndromic disease, rather than an isolated early-onset dystonia, which has been the classic view of the condition.
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The lysine methyltransferase 2B (KMT2B) gene product is important for epigenetic modifications associated with active gene transcription in normal development and in maintaining proper neural function. Pathogenic variants in KMT2B have been associated with childhood-onset Dystonia-28 and Intellectual developmental disorder, autosomal dominant 68 (MRD 68) for cases of neurodevelopmental impairment without dystonia (DYT28; OMIM 617284 and MRD68; OMIM 619934, respectively). Since its first description in 2016, approximately one hundred KMT2B genetic variants have been reported with heterogeneous phenotypes, including atypical patterns of dystonia evolution and non-dystonic neurodevelopmental phenotypes.
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Department of Neurology, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, Karnataka, India.
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