A New Pathologic KMT2B Variant Associated with Childhood Onset Dystonia Presenting as Variable Phenotypes among Family Members.

Background: KMT2B-related dystonia is a primarily childhood-onset movement disorder characterized by progressive dystonia, spasticity, and developmental delay. A minority of individuals possess an inherited KMT2B variant. Case Report: As a child, the proband experienced mild developmental delay and laryngeal dystonia which progressed to generalized dystonia. Patellar hyperreflexia, postural tremor, and everted gait were documented. Whole exome sequencing identified a heterozygous pathogenic KMT2B variant in the proband, proband's sister, and proband's mother who had milder presentations. Discussion: This novel KMT2B variant reflects intrafamilial variable expressivity in KMT2B-related dystonia. Further identification of variants will allow for better appreciation of the phenotypic spectrum.