Adult-Onset KMT2B-Related Dystonia Responsive to Deep Brain Stimulation

Clinical and genetic profile of patients with dystonia: An experience from a tertiary neurology center from India

BACKGROUND

The genetics of dystonia have varied across different ethnicities worldwide. Its significance has become more apparent with the advent of deep brain stimulation.

OBJECTIVE

To study the clinico-genetic profile of patients with probable genetic dystonia using whole exome sequencing (WES).

METHODS

A prospective, cross-sectional study was conducted from May 2021 to September 2022, enrolling patients with dystonia of presumed genetic etiology for WES. The study compared genetically-determined cases harboring pathogenic/likely-pathogenic variants (P/LP subgroup) with the presumed idiopathic or unsolved cases.

RESULTS

We recruited 65 patients (males, 69.2%) whose mean age of onset (AAO) and assessment were 25.0 ± 16.6 and 31.7 ± 15.2 years, respectively. Fifteen had pathogenic/likely-pathogenic variants (yield = 23.1%), 16 (24.6%) had variants of uncertain significance (VUS), 2 were heterozygous carriers while the remaining 32 cases tested negative (presumed idiopathic group). The P/LP subgroup had a significantly younger AAO (16.8 ± 12.3 vs 31.3 ± 17.0 years, p = 0.009), longer duration of illness (10.9 ± 10.3 vs 4.8 ± 4.3 years, p = 0.006), higher prevalence of generalized dystonia (n = 12, 80.0% vs n = 10, 31.3%, p = 0.004), lower-limb onset (n = 5, 33.3% vs n = 1, 3.1%, p = 0.009), higher motor (p = 0.035) and disability scores (p = 0.042). The classical DYT genes with pathogenic/likely pathogenic variants included 3 cases each of TOR1A, and KMT2B, and single cases each of SGCE, EIF2AK2, and VPS16. Non-DYT pathogenic/likely-pathogenic cases included PINK1, PANK2, CTSF, POLG, MICU1, and TSPOAP1.

CONCLUSIONS

The yield of WES was 23.1% among cases of probable genetic dystonia. Pathogenic or likely pathogenic variants in TOR1A, KMT2B, and SGCE genes were commoner. The absence of family history emphasizes the importance of accurate assessment of clinical predictors before genetic testing.

KMT2B-Related Dystonia in Indian Patients With Literature Review and Emphasis on Asian Cohort

OBJECTIVE

aaMutations in the KMT2B gene have been identified in patients previously diagnosed with idiopathic dystonia. Literature on KMT2B-related dystonia is sparse in the Indian and Asian populations.

METHODS

aaWe report seven patients with KMT2B-related dystonia studied prospectively from May 2021 to September 2022. Patients underwent deep clinical phenotyping and genetic testing by whole-exome sequencing (WES). A systematic literature search was performed to identify the spectrum of previously published KMT2B-related disorders in the Asian subcontinent.

RESULTS

aaThe seven identified patients with KMT2B-related dystonia had a median age at onset of four years. The majority experienced onset in the lower limbs (n = 5, 71.4%), with generalization at a median duration of 2 years. All patients except one had complex phenotypes manifesting as facial dysmorphism (n = 4), microcephaly (n = 3), developmental delay (n = 3), and short stature (n = 1). Magnetic resonance imaging (MRI) abnormalities were present in four cases. WES revealed novel mutations in the KMT2B gene in all patients except one. Compared to the largest cohort of patients with KMT2B-related disorders, the Asian cohort, comprising 42 patients, had a lower prevalence of female patients, facial dysmorphism, microcephaly, intellectual disability, and MRI abnormalities. Protein-truncating variants were more prevalent than missense variants. While microcephaly and short stature were more common in patients with missense mutations, facial dysmorphism was more common in patients with truncating variants. Deep brain stimulation, performed in 17 patients, had satisfactory outcomes.

CONCLUSION

aaThis is the largest series of patients with KMT2B-related disorders from India, further expanding the clinico-genotypic spectrum. The extended Asian cohort emphasizes the unique attributes of this part of the world.

GPi DBS treatment outcome in children with monogenic dystonia: a case series and review of the literature

Introduction

Dystonia is the third most common pediatric movement disorder and is often difficult to treat. Deep brain stimulation (DBS) of the internal pallidum (GPi) has been demonstrated as a safe and effective treatment for genetic dystonia in adolescents and adults. The results of DBS in children are limited to individual cases or case series, although it has been proven to be an effective procedure in carefully selected pediatric cohorts. The aim of our study was to present the treatment outcome for 7- to 9-year-old pediatric patients with disabling monogenic isolated generalized DYT-THAP1 and DYT-KMT2B dystonia after bilateral GPi-DBS.

Patients and results

We present three boys aged <10 years; two siblings with disabling generalized DYT-THAP1 dystonia and a boy with monogenic-complex DYT-KMT2B. Dystonia onset occurred between the ages of 3 and 6. Significantly disabled children were mostly dependent on their parents. Pharmacotherapy was inefficient and patients underwent bilateral GPi-DBS. Clinical signs of dystonia improved significantly in the first month after the implantation and continued to maintain improved motor functions, which were found to have improved further at follow-up. These patients were ambulant without support and included in everyday activities. All patients had significantly lower Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) values, indicating >25% improvement over the first 15 months. However, there was a decline in speech and upper limb function, manifesting with bradylalia, bradykinesia, and dysphonia, which decreased after treatment with trihexyphenidyl.

Conclusion

Although reports of patients with monogenic dystonia, particularly DYT-THAP1, treated with DBS are still scarce, DBS should be considered as an efficient treatment approach in children with pharmacoresistent dystonia, especially with generalized monogenic dystonia and to prevent severe and disabling symptoms that reduce the quality of life, including emotional and social aspects. Patients require an individual approach and parents should be properly informed about expectations and possible outcomes, including relapses and impairments, in addition to DBS responsiveness and related improvements. Furthermore, early genetic diagnosis and the provision of appropriate treatments, including DBS, are mandatory for preventing severe neurologic impairments.

Dystonic Tremor in Adult-onset DYT-KMT2B

KMT2B-related dystonia (DYT28, DYT-KMT2B) is an inherited dystonia that generally begins in the lower limbs during childhood and evolves into generalized dystonia. We herein report a case of adult-onset DYT28 with dystonic tremor. A 27-year-old woman initially displayed right upper limb and cervical tremors over the course of 1 year. A neurological examination also revealed cervical and lower limb dystonia. Although the disease generally develops during childhood, we diagnosed the woman with DYT28, as genetic testing revealed a mutation in KMT2B. Adult-onset patients with DYT28 might also show uncommon symptoms as well as DYT-TOR1A (DYT1).

GPi-DBS for KMT2B-Associated Dystonia: Systematic Review and Meta-Analysis

Background

Early evidence suggests good response to pallidal deep brain stimulation (DBS) in DYT-KMT2B.

Objectives

We aimed to conduct a systematic review and meta-analysis to assess outcomes and identify predictors of good outcome following GPi-DBS in DYT-KMT2B.

Methods

We searched MEDLINE, Cochrane and MDS-abstracts databases using the MeSH terms "KMT2B and DYT28". We included studies that reported objective outcomes following GPi-DBS in DYT-KMT2B. The BFMDRS-M (Burke-Fahn-Marsden Dystonia Rating Scale- Movement) total scores pre- and post-surgery were used to quantify outcomes. We calculated pooled effects using a random effects meta-analysis and used meta-regression to identify potential effect modifiers. Multiple linear regression using individual patient data was used to identify predictors of good outcome (>50% improvement from baseline on BFMDRS-M).

Results

Initial searches screened 132 abstracts of which 34 full-text articles were identified to be of potential interest. Ten studies reporting 42 individual patients, met the inclusion/exclusion criteria and were included in the final review. The mean age at onset was 6.4 ± 5.7 years and 40% were male. The median follow-up was 12 months (range: 1-264 months). GPi-DBS resulted in median BFMDRS-M improvement of 42.7% (range: -103.5% to 95.9%) postoperatively. Pooled proportion of patients experiencing clinical improvement >50% on BFMDRS-M was 41% (95% CI: 27%-57%). Male gender [β: 22.6, 95% CI: 8.0-37.3, P = 0.004), and higher pre-operative BFMDRS-M score [β: 0.62, 95% CI: 0.36-0.87, P < 0.001) were independently associated with better outcome.

Conclusion

KMT2B-associated dystonia responds effectively to pallidal stimulation. The outcome is better in males and those with more severe dystonia at baseline.

A practical guide to troubleshooting pallidal deep brain stimulation issues in patients with dystonia

High frequency deep brain stimulation (DBS) of the internal portion of the globus pallidus has, in the last two decades, become a mainstream therapy for the management of medically-refractory dystonia syndromes. Such increasing uptake places an onus on movement disorder physicians to become familiar with this treatment modality, in particular optimal patient selection for the procedure and how to troubleshoot problems relating to sub-optimal efficacy and therapy-related side effects. Deep brain stimulation for dystonic conditions presents some unique challenges. For example, the frequent lack of immediate change in clinical status following stimulation alterations means that programming often relies on personal experience and local practice rather than real-time indicators of efficacy. Further, dystonia is a highly heterogeneous disorder, making the development of unifying guidelines and programming algorithms for DBS in this population difficult. Consequently, physicians may feel less confident in managing DBS for dystonia as compared to other indications e.g. Parkinson's disease. In this review, we integrate our years of personal experience of the programming of DBS systems for dystonia with a critical appraisal of the literature to produce a practical guide for troubleshooting common issues encountered in patients with dystonia treated with DBS, in the hope of improving the care for these patients.