Objective: This study aims to characterize the phenotypic spectrum and therapeutic responses to Deep Brain Stimulation (DBS) in Chilean patients diagnosed with dystonia due to KMT2B gene variants.

Background: Dystonia associated with variants in the KMT2B gene is a hyperkinetic movement disorder usually manifested in childhood. It is characterized by focal dystonia in the lower limbs that progressively generalizes, often involving significant cervical, cranial, and laryngeal areas.

Method: This prospective study involved six Chilean patients diagnosed with dystonia owing to KMT2B gene variants, confirmed through genetic testing. Comprehensive neurological assessments documented symptoms of cranial, laryngeal, and limb dystonia, while magnetic resonance imaging (MRI) excluded structural abnormalities. Dystonia severity was measured using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). Treatment responses were collected for both antidystonic medications and DBS outcomes.

Results: We analyzed six patients (two males and four females) with an average symptom onset age of 5 years. Four patients presented with dysarthria followed by focal dystonia that generalized, while two experienced frequent falls alongside focal dystonia, later complicated by laryngeal symptoms. All patients exhibited normal MRI findings and significant variability in BFMDRS movement scale (21 to 105 points) with poor responses to pharmacotherapy. All patients underwent DBS; five were implanted with electrodes in the Internal Globus Pallidus (Gpi), while one required bilateral implantation in both the Internal Globus Pallidus and the Subthalamic Nucleus. Clinical responses to DBS varied, with reductions in BFMDRS movement scale ranging from 25% to 50%, resulting in an average reduction of 32%. Additionally, two patients progressed to dystonic status during the course of the study.

Conclusion: We present a series of Chilean patients diagnosed with DYT-KMT2B dystonia. All patients exhibited cranial, laryngeal, and limb dystonia, with initial symptoms predominantly characterized by dysarthria and focal dystonia in the lower extremities. The effectiveness of antidystonic medications was limited across all cases. Nevertheless, all patients underwent DBS treatment, which resulted in positive therapeutic outcomes.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/phenotypic-spectrum-and-response-to-deep-brain-stimulation-dbs-in-patients-with-dystonia-due-to-variants-in-the-kmt2b-gene-a-description-of-six-chilean-cases/