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.
Keywords: DYT-28; KMT2B; MLL4; complex dystonia; dystonia; variable expressivity.
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