Clinical phenotypes, genotypes and treatment in Chinese dystonia patients with KMT2B variants

The clinical spectrum and pathogenesis associated with KMT2B variants in Chinese pediatric patients

OBJECTIVE

To evaluate the clinical spectrum and pathogenesis associated with KMT2B variants in Chinese children with dystonia or developmental delay.

METHODS

We reported twenty-seven (fourteen males and thirteen females) pediatric patients with KMT2B variants identified via next-generation sequencing from a single Chinese center. Moreover, transcriptomics and proteomics assays were performed on fibroblasts from patients with different genotypes to investigate the pathogenic mechanisms involved.

RESULTS

Twenty-six patients had dystonia including generalized dystonia (n = 19), multifocal dystonia (n = 6), and segmental dystonia (n = 1), and one patient had nondystonic severe-developmental delay (DD). All the twenty-six patients had complex dystonia compounded with other manifestations of movement disorders (tremor (n = 6), myoclonus (n = 5), status dystonicus (n = 2), and tic (n = 1)) or dysmorphic features and developmental delay. The onset of dystonia was between 1 month and 13 years 8 months (median 4 years 4 months). Dystonia was aggravated by fever (n = 11), and diurnal and climate fluctuations (n = 4). Eleven patients underwent deep brain stimulation and experienced significant improvements in motor function and disability. We identified twenty-six intragenic heterozygous KMT2B pathogenic variants and one Chr:19q13.12 contiguous gene deletion. Sixteen variants were novel. Differentially expressed genes induced by KMT2B variants were significantly enriched for mitochondria-related biological processes in patient fibroblasts. As a result, mitochondrial morphology of mitochondria was altered, and aerobic respiration was impaired.

CONCLUSION

Our study reports the pediatric cases of KMT2B-related disorder from a single center in China. Additionally, our study highlights the role of KMT2B variants in mitochondrial dysfunction.

Diagnostic utility of DNA methylation episignature analysis for early diagnosis of KMT2B-related disorders: case report

The lysine methyltransferase 2B (KMT2B) gene product is important for epigenetic modifications associated with active gene transcription in normal development and in maintaining proper neural function. Pathogenic variants in KMT2B have been associated with childhood-onset Dystonia-28 and Intellectual developmental disorder, autosomal dominant 68 (MRD 68) for cases of neurodevelopmental impairment without dystonia (DYT28; OMIM 617284 and MRD68; OMIM 619934, respectively). Since its first description in 2016, approximately one hundred KMT2B genetic variants have been reported with heterogeneous phenotypes, including atypical patterns of dystonia evolution and non-dystonic neurodevelopmental phenotypes. KMT2B-related disorders share many overlapping phenotypic characteristics with other neurodevelopmental disorders and delayed dystonia, that can appear later in childhood, often delaying clinical diagnosis. Furthermore, conventional genetic testing may not always provide actionable information (e.g., gene panel selection based on early clinical presentation or variants of uncertain significance), which prevents patients and families from obtaining early access to treatments and support. Herein, we describe the early diagnosis of KMT2B-related neurodevelopmental disorder by DNA methylation episignature testing in a 4-year-old patient without features of dystonia at diagnosis, which is reported to develop in more than 80% of KMT2B-related disorder cases. The proband, a 4-year-old female of Jewish-Israeli descent, presented with speech delay, microcephaly, poor weight gain, attention-deficit and hyperactivity disorder, dysmorphism, intellectual disabilities and joint hyperlaxity, but presented no signs of dystonia at initial evaluation. Episignature screening in this pre-symptomatic patient enabled accurate genetic diagnosis and timely and actionable intervention earlier in the natural history of Childhood-onset Dystonia-28.

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.

-Related Dystonia: Challenges in Diagnosis and Treatment

In this study, we report the first known Turkish case of a novel nonsense mutation c.2453dupT (p.M818fs*28) in the <i>KMT2B</i> (NM_014727.2) gene diagnosed in a male patient with <i>KMT2B</i>-related dystonia (DYT-<i>KMT2B</i>, DYT-28, Dystonia*-28), which is a complex, childhood-onset, progressive, hereditary dystonia. The patient, who is followed up from 9 to 13 years of age, had dysmorphic features, developmental delay, short stature, and microcephaly, in addition to focal dystonia and hemichorea (in the right and left lower extremities). Generalized dystonia involving bulbar and cervical muscles, in addition to dystonic cramps, myoclonus, and hemiballismus, were also observed during the course of the follow-up. While he was able to perform basic functions like eating, climbing stairs, walking, and writing with the aid of levodopa and trihexyphenidyl treatment, his clinical status gradually deteriorated secondary to progressive generalized dystonia in the 4-year follow-up. Deep brain stimulation has been shown to be effective in several patients which could be the next preferred treatment for the patient.

Pallidal Deep Brain Stimulation for KMT2B Related Dystonia in An Indian Patient

Outcomes of pallidal stimulation in KMT2B dystonia have been infrequently reported prospectively. We report the six-month outcomes of bilateral GPi DBS in an Asian Indian patient with early-onset generalized dystonia associated with a novel heterozygous variant in the KMT2B gene.

Deep Brain Stimulation in KMT2B-Related Dystonia: Case Report and Review of the Literature With Special Emphasis on Dysarthria and Speech

Objective: KMT2B-related dystonia is a progressive childhood-onset movement disorder, evolving from lower-limb focal dystonia into generalized dystonia. With increasing age, children frequently show prominent laryngeal or facial dystonia manifesting in dysarthria. Bilateral deep brain stimulation of the globus pallidus internus (GPi-DBS) is reported to be an efficient therapeutic option. Especially improvement of dystonia and regaining of independent mobility is commonly described, but detailed information about the impact of GPi-DBS on dysarthria and speech is scarce. Methods: We report the 16-months outcome after bilateral GPi-DBS in an 8-year-old child with KMT2B-related dystonia caused by a de-novo c.3043C>T (p.Arg1015^*) non-sense variant with special emphasis on dysarthria and speech. We compare the outcome of our patient with 59 patients identified through a PubMed literature search. Results: A remarkable improvement of voice, articulation, respiration and prosodic characteristics was seen 16 months after GPi-DBS. The patients' speech intelligibility improved. His speech became much more comprehensible not only for his parents, but also for others. Furthermore, his vocabulary and the possibility to express his feelings and wants expanded considerably. Conclusion: A positive outcome of GPi-DBS on speech and dysarthria is rarely described in the literature. This might be due to disease progression, non-effectiveness of DBS or due to inadvertent spreading of the electrical current to the corticobulbar tract causing stimulation induced dysarthria. This highlights the importance of optimal lead placement, the possibility of horizontal steering of the electrical field by applying directional stimulation with segmented leads as well as the use of the lowest possible effective stimulation intensity.

The Efficacy and Predictors of Using GPi-DBS to Treat Early-Onset Dystonia: An Individual Patient Analysis

OBJECTIVE

To compare the efficacy in patients with different genotypes, identify the potential predictive factors, and summarize the complications of globus pallidus deep brain stimulation (GPi-DBS) treating early-onset dystonia.

METHODS

Three electronic databases (PubMed, Embase, and Cochrane databases) were searched with no publication data restriction. The primary outcomes were the improvements in Burke-Fahn-Marsden Dystonia Rating Scale motor (BFMDRS-M) and disability (BFMDRS-D) score. Pearson's correlation coefficients and a metaregression analysis were used to identify the potential predictive factors. This article was registered in Prospero (CRD42020188527).

RESULTS

Fifty-four studies (231 patients) were included. Patients showed significant improvement rate in BFMDRS-M (60.6%, p < 0.001) and BFMDRS-D (57.5%, p < 0.001) scores after treatment with GPi-DBS. BFMDRS-M score improved greater in the DYT-1-positive (p = 0.001) and DYT-11-positive (p = 0.008) patients compared to DYT-6-positive patients. BFMDRS-D score improved greater in the DYT-11 (+) compared to DYT-6 (+) patients (p = 0.010). The relative change of BFMDRS-M (p = 0.002) and BFMDRS-D (p = 0.010) scores was negatively correlated with preoperative BFMDRS-M score. In the metaregression analysis, the best predictive model showed that preoperative BFMDRS-M, disease duration (p = 0.047), and the age at symptom onset (p = 0.027) were important.

CONCLUSION

Patients with early-onset dystonia have a significant effect after GPi-DBS treatment, and DYT-1 (+) and DYT-11 (+) patients are better candidates for GPi-DBS. Lower preoperative score, later age of onset, and an earlier age at surgery probably predict better clinical outcomes.

Genotype-Phenotype Relations for Isolated Dystonia Genes: MDSGene Systematic Review

This comprehensive MDSGene review is devoted to 7 genes - TOR1A, THAP1, GNAL, ANO3, PRKRA, KMT2B, and HPCA - mutations in which may cause isolated dystonia. It followed MDSGene's standardized data extraction protocol and screened a total of ~1200 citations. Phenotypic and genotypic data on ~1200 patients with 254 different mutations were curated and analyzed. There were differences regarding age at onset, site of onset, and distribution of symptoms across mutation carriers in all 7 genes. Although carriers of TOR1A, THAP1, PRKRA, KMT2B, or HPCA mutations mostly showed childhood and adolescent onset, patients with GNAL and ANO3 mutations often developed first symptoms in adulthood. GNAL and KMT2B mutation carriers frequently have 1 predominant site of onset, that is, the neck (GNAL) or the lower limbs (KMT2B), whereas site of onset in DYT-TOR1A, DYT-THAP1, DYT-ANO3, DYT-PRKRA, and DYT-HPCA was broader. However, in most DYT-THAP1 and DYT-ANO3 patients, dystonia first manifested in the upper half of the body (upper limb, neck, and craniofacial/laryngeal), whereas onset in DYT-TOR1A, DYT-PRKRA and DYT-HPCA was frequently observed in an extremity, including both upper and lower ones. For ANO3, a segmental/multifocal distribution was typical, whereas TOR1A, PRKRA, KMT2B, and HPCA mutation carriers commonly developed generalized dystonia. THAP1 mutation carriers presented with focal, segmental/multifocal, or generalized dystonia in almost equal proportions. GNAL mutation carriers rarely showed generalization. This review provides a comprehensive overview of the current knowledge of hereditary isolated dystonia. The data are also available in an online database (http://www.mdsgene.org), which additionally offers descriptive summary statistics. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Genetic Dystonias: Update on Classification and New Genetic Discoveries

PURPOSE OF REVIEW

Since the advent of next-generation sequencing, the number of genes associated with dystonia has been growing exponentially. We provide here a comprehensive review of the latest genetic discoveries in the field of dystonia and discuss how the growing knowledge of biology underlying monogenic dystonias may influence and challenge current classification systems.

RECENT FINDINGS

Pathogenic variants in genes without previously confirmed roles in human disease have been identified in subjects affected by isolated or combined dystonia (KMT2B, VPS16, HPCA, KCTD17, DNAJC12, SLC18A2) and complex dystonia (SQSTM1, IRF2BPL, YY1, VPS41). Importantly, the classical distinction between isolated and combined dystonias has become harder to sustain since many genes have been shown to determine multiple dystonic presentations (e.g., ANO3, GNAL, ADCY5, and ATP1A3). In addition, a growing number of genes initially linked to other neurological phenotypes, such as developmental delay, epilepsy, or ataxia, are now recognized to cause prominent dystonia, occasionally in an isolated fashion (e.g., GNAO1, GNB1, SCN8A, RHOBTB2, and COQ8A). Finally, emerging analyses suggest biological convergence of genes linked to different dystonic phenotypes. While our knowledge on the genetic basis of monogenic dystonias has tremendously grown, their clinical boundaries are becoming increasingly blurry. The current phenotype-based classification may not reflect the molecular structure of the disease, urging the need for new systems based on shared biological pathways among dystonia-linked genes.

Pallidal Deep Brain Stimulation for Monogenic Dystonia: The Effect of Gene on Outcome

Globus pallidus internus deep brain stimulation (GPi DBS) is the most effective intervention for medically refractory segmental and generalized dystonia in both children and adults. Predictive factors for the degree of improvement after GPi DBS include shorter disease duration and dystonia subtype with idiopathic isolated dystonia usually responding better than acquired combined dystonias. Other factors contributing to variability in outcome may include body distribution, pattern of dystonia and DBS related factors such as lead placement and stimulation parameters. The responsiveness to DBS appears to vary between different monogenic forms of dystonia, with some improving more than others. The first observation in this regard was reports of superior DBS outcomes in DYT-TOR1A (DYT1) dystonia, although other studies have found no difference. Recently a subgroup with young onset DYT-TOR1A, more rapid progression and secondary worsening after effective GPi DBS, has been described. Myoclonus dystonia due to DYT-SCGE (DYT11) usually responds well to GPi DBS. Good outcomes following GPi DBS have also been documented in X-linked dystonia Parkinsonism (DYT3). In contrast, poorer, more variable DBS outcomes have been reported in DYT-THAP1 (DYT6) including a recent larger series. The outcome of GPi DBS in other monogenic isolated and combined dystonias including DYT-GNAL (DYT25), DYT-KMT2B (DYT28), DYT-ATP1A3 (DYT12), and DYT-ANO3 (DYT24) have been reported with varying results in smaller numbers of patients. In this article the available evidence for long term GPi DBS outcome between different genetic dystonias is reviewed to reappraise popular perceptions of expected outcomes and revisit whether genetic diagnosis may assist in predicting DBS outcome.