Reviewing the Clinical Spectrum Related to Kmt2b Gene Mutations: Unusual Clinical Presentation and a Possible New Pathogenic Mutation
Abstract Introduction KMT2B related dystonia is a childhood onset generalized dystonia. Since its first description in 2016, different phenotypic spectrum have been reported. The aim of the case report is to provide data that may help to understand the spectrum of KMT2B-related disorders. We present two members of a family with a possible non-previously described pathogenic mutation and an unusual KMT2B related dystonia presentation: an adult onset and focal dystonia.Case Presentation The index patient is a 32 year-old woman with a generalized dystonia. Her maternal uncle presented a focal dystonia. Next-generation sequencing revealed a heterozygous missense mutation in KMT2B gene (19q13.12), described as a variant of uncertain significance (VUS). Although characteristic phenotype of KMT2B dystonia is a childhood onset generalized dystonia, different phenotypes have been related according to the kinds of mutations in this gene, also varying the age of symptom onset and the penetrance of the mutation. Asymptomatic or sub-clinical carriers and adult onset has been described. Due to the low prevalence of this variant in the general population and the low penetrance and high intrafamilial variability of this entity, we suggest that this mutation might be a pathogenic variant.ConclusionsKMT2B related dystonia is an emerging and prevalent monogenic dystonia whose incidence, genetic variability and clinical spectrum remain unknown. Despite the study of this gene is indicated in childhood onset dystonia, description of cases such as ours shows that its sequencing in patients with an adult-onset dystonia with family history can be useful for the diagnosis.