KMT2B rare missense variants in generalized dystonia

Background: Recently a novel syndrome of childhood-onset generalized dystonia originating from mutations in lysine-specific methyltransferase 2B (KMT2B) has been reported. Methods: We sequenced the exomes of 4 generalized dystonia-affected probands recruited from a Prague movement disorders center (Czech Republic). Bioinformatics analyses were conducted to select candidate causal variants in described dystonia-mutated genes. After cosegregation testing, checklists from the American College of Medical Genetics and Genomics were adopted to judge variant pathogenicity. Results: Three novel, predicted protein-damaging missense variants in KMT2B were identified (p.Glu1234Lys, p.Ala1541Val, p.Arg1779Gln). Meeting pathogenicity criteria, p.Glu1234Lys was absent from population-based controls, situated in a key protein domain, and had occurred de novo. The associated phenotype comprised adolescence-onset generalized isolated dystonia with prominent speech impairment. Although linked to a similar clinical expression, p.Ala1541Val and p.Arg1779Gln remained of uncertain significance. Conclusions: Rare missense variation in KMT2B represents an additional cause of generalized dystonia. Application of sequence interpretation standards is required before assigning pathogenicity to a KMT2B missense variant.