De-novo KMT2B mutation in a consanguineous family: 15-Year follow-up of an Afghan dystonia patient

Genetic testing for non-parkinsonian movement disorders: Navigating the diagnostic maze

Genetic testing has become a valuable diagnostic tool for movement disorders due to substantial advancements in understanding their genetic basis. However, the heterogeneity of movement disorders poses a significant challenge, with many genes implicated in different subtypes. This paper aims to provide a neurologist's perspective on approaching patients with hereditary hyperkinetic disorders with a focus on select forms of dystonia, paroxysmal dyskinesia, chorea, and ataxia. Age at onset, initial symptoms, and their severity, as well as the presence of any concurrent neurological and non-neurological features, contribute to the individual clinical profiles of hereditary non-parkinsonian movement disorders, aiding in the selection of appropriate genetic testing strategies. There are also more specific diagnostic clues that may facilitate the decision-making process and may be highly specific for certain conditions, such as diurnal fluctuations and l-dopa response in dopa-responsive dystonia, and triggering factors, duration and frequency of attacks in paroxysmal dyskinesia. While the genetic and mutational spectrum across non-parkinsonian movement disorders is broad, certain groups of diseases tend to be associated with specific types of pathogenic variants, such as repeat expansions in many of the ataxias. Some of these pathogenic variants cannot be detected by standard methods, such as panel or exome sequencing, but require the investigation of intronic regions for repeat expansions, such as Friedreich's or FGF14-linked ataxia. With our advancing knowledge of the genetic underpinnings of movement disorders, the incorporation of precise and personalized diagnostic strategies can enhance patient care, prognosis, and the application and development of targeted therapeutic interventions.

Large-Scale Screening: Phenotypic and Mutational Spectrum in Isolated and Combined Dystonia Genes

BACKGROUND

Pathogenic variants in several genes have been linked to genetic forms of isolated or combined dystonia. The phenotypic and genetic spectrum and the frequency of pathogenic variants in these genes have not yet been fully elucidated, neither in patients with dystonia nor with other, sometimes co-occurring movement disorders such as Parkinson's disease (PD).

OBJECTIVES

To screen >2000 patients with dystonia or PD for rare variants in known dystonia-causing genes.

METHODS

We screened 1207 dystonia patients from Germany (DysTract consortium), Spain, and South Korea, and 1036 PD patients from Germany for pathogenic variants using a next-generation sequencing gene panel. The impact on DNA methylation of KMT2B variants was evaluated by analyzing the gene's characteristic episignature.

RESULTS

We identified 171 carriers (109 with dystonia [9.0%]; 62 with PD [6.0%]) of 131 rare variants (minor allele frequency <0.005). A total of 52 patients (48 dystonia [4.0%]; four PD [0.4%, all with GCH1 variants]) carried 33 different (likely) pathogenic variants, of which 17 were not previously reported. Pathogenic biallelic variants in PRKRA were not found. Episignature analysis of 48 KMT2B variants revealed that only two of these should be considered (likely) pathogenic.

CONCLUSION

This study confirms pathogenic variants in GCH1, GNAL, KMT2B, SGCE, THAP1, and TOR1A as relevant causes in dystonia and expands the mutational spectrum. Of note, likely pathogenic variants only in GCH1 were also found among PD patients. For DYT-KMT2B, the recently described episignature served as a reliable readout to determine the functional effect of newly identified variants. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

Radiofrequency ablation for DYT-28 dystonia: short term follow-up of three adult cases

Mutations in the lysine methyltransferase 2B (KMT2B) gene have recently been reported to be associated with childhood‐onset generalized dystonia. There have been no studies investigating ablative treatments for the management of this disorder. Three patients underwent either a staged unilateral pallidotomy and contralateral pallidothalamic tractotomy (19‐year‐old man, 2‐year follow‐up), a unilateral pallidothalamic tractotomy (34‐year‐old man, 6‐month follow‐up) or a simultaneous unilateral pallidothalamic tractotomy and ventro‐oral thalamotomy (29‐year‐old man, 6‐month follow‐up). The average total patient score on the Burke‐Fahn‐Marsden Dystonia Rating Scale‐Movement Scale improved from 39.5 to 13.2 (66.6%) after the procedures. No significant complications were identified. Ablative treatments appear to be a promising alternative surgical option for generalized dystonia with KMT2B mutation.

Failure to thrive - an overlooked manifestation of KMT2B-related dystonia: a case presentation

Background

KMT2B-related dystonia is a recently described form of childhood onset dystonia that may improve with deep brain stimulation. Prior reports have focused on neurologic features including prominent bulbar involvement without detailing general health consequences that may result from orolingual dysfunction. We describe a family with novel KMT2B mutation with several members with failure to thrive to highlight this non-neurologic, but consequential impact of mutation in this gene.

Case presentation

We present a case of a 15-year old female who was admitted and evaluated for failure to thrive. On exam, she had severe speech dysfluency, limited ability to protrude the tongue, and generalized dystonia involving the oromandibular region, right upper and left lower extremity with left foot inversion contracture. The proband and her parents underwent whole genome sequencing. A previously undescribed variant, c.4960 T > C (p.Cys1654Arg), was identified in the KMT2B gene in the proband and mother, and this variant was subsequently confirmed in two maternal cousins, one with failure to thrive. Literature review identified frequent reports of prominent bulbar involvement but failure to thrive is rarely mentioned.

Conclusion

Failure to thrive is a common pediatric clinical condition that has consequences for growth and development. In the presence of an abnormal neurologic exam, a search for a specific underlying genetic etiology should be pursued. With this case series, we highlight an unusual potentially treatable cause of failure to thrive, reinforce the importance of precise molecular diagnosis for patients with failure to thrive and an abnormal neurologic exam, and underscore the importance of cascade screening of family members.

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

BACKGROUND

KMT2B-related dystonia is a recently discovered hereditary dystonia that mostly occurs in childhood. This dystonia usually progresses to generalized dystonia with cervical, cranial, pharynx and larynx involvement. Our study summarizes genotype-phenotype features and deep brain stimulation (DBS) efficacy observed with KMT2B-related dystonia patients in China.

METHODS

We identified 20 patients with KMT2B variations from dystonia samples with a gene panel and whole exome sequencing. Genetic, clinical and treatment analyses of these patients with KMT2B mutations were further conducted.

RESULTS

We summarized the genotype and phenotypic characteristics of KMT2B-related patients in China, including 16 sporadic patients and 3 pedigrees (including 4 patients). Thirty-five percent (7/20) of patients had been published previously. The age of onset was between 1 month and 24 years (average 6.90 ± 5.72 years). Sixty-five percent (13/20) of patients had onset from lower limbs. Upper limbs or larynx accounted for 15% (3/20) and 20% (4/20) of patients, respectively. In the same family, male patients tended to have more severe symptoms than female patients. Carriers of KMT2B variants may present with nonmotor symptoms without dystonia. Abnormal endocrine metabolism could also be seen in our patients, including advanced bone age that had never been reported previously. Nine of our patients underwent DBS surgery. The mean follow-up time was 4.9 (range 1.3-16) months after DBS, and perceptible improvement of clinical symptoms were observed.

CONCLUSIONS

The genotypic and phenotypic spectra of Chinese KMT2B-related dystonia patients were further expanded. DBS surgery might be the preferred option for severe KMT2B-related dystonia patients till now.

Update on KMT2B-Related Dystonia

PURPOSE OF REVIEW

To summarize the molecular and clinical findings of KMT2B-related dystonia (DYT-KMT2B), a newly identified genetic dystonia syndrome.

RECENT FINDINGS

Since first described in 2016, 66 different KMT2B-affecting variants, encompassing a set of frameshift, nonsense, splice-site, missense, and deletion mutations, have been reported in 76 patients. Most mutations are de novo and expected to mediate epigenetic dysregulation by inducing KMT2B haploinsufficiency. DYT-KMT2B is characterized phenotypically by limb-onset childhood dystonia that tends to spread progressively, resulting in generalized dystonia with cranio-cervical involvement. Co-occuring signs such as intellectual disability are frequently observed. Sustained response to deep brain stimulation (DBS), including restoration of independent ambulation, is seen in 93% (27/29) of patients. DYT-KMT2B is emerging as a prevalent monogenic dystonia. Childhood-onset dystonia presentations should prompt a search for KMT2B mutations, preferentially via next-generation-sequencing and genomic-array technologies, to enable specific counseling and treatment. Prospective multicenter studies are desirable to establish KMT2B mutational status as a DBS outcome predictor.

Identification of Novel KMT2B Variants in Chinese Dystonia Patients via Whole-Exome Sequencing

Background: Dystonia is a movement disorder with high clinical and genetic heterogeneity. Recently mutations in lysine-specific histone methyltransferase 2B (KMT2B) gene have been reported to be associated with early-onset progressive dystonia.

Methods: We performed whole-exome sequencings (WES) in a cohort of early-onset dystonia patients from China. Bioinformatics analysis and cosegregation testings were conducted to select candidate causal variants. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

Results: Three novel KMT2B variants were identified, including p.Q1359^* in patient 1, p.R1487AfsTer7 in patient 2, and p.R152W in patient 3. Among these variants, the nonsense variant p.Q1359^* and the frameshift variant p.R1487AfsTer7 showed high pathogenicity and were rated as pathogenic according to the ACMG guideline. Regarding the phenotypes of these two patients with pathogenic variants, patient 2 showed the similar presentation as reported whereas patient 1 seemly harbored the atypical presentations, including later onset age, atypical sites of onset and milder degree of dystonia.

Conclusions: We further report three dystonia patients with novel variants in KMT2B and expand the spectrums of genotype and phenotype of KMT2B.

Frequency and phenotypic spectrum of KMT2B dystonia in childhood: A single-center cohort study

BACKGROUND

Childhood-onset dystonia is often genetically determined. Recently, KMT2B variants have been recognized as an important cause of childhood-onset dystonia.

OBJECTIVE

To define the frequency of KMT2B mutations in a cohort of dystonic patients aged <18 years at onset, the associated clinical and radiological phenotype, and the natural history of disease.

METHODS

Whole-exome sequencing or customized gene panels were used to screen a cohort of 65 patients who had previously tested negative for all other known dystonia-associated genes.

RESULTS

We identified 14 patients (21.5%) carrying KMT2B variants, of which 1 was classified as a variant of unknown significance. We also identified 2 additional patients carrying pathogenic mutations in GNAO1 and ATM. Overall, we established a definitive genetic diagnosis in 23% of cases. We observed a spectrum of clinical manifestations in KMT2B variant carriers, ranging from generalized dystonia to short stature or intellectual disability alone, even within the same family. In 78.5% of cases, dystonia involved the lower limbs at onset, with later caudocranial generalization. Eight patients underwent pallidal DBS with a median decrease of Burke-Fahn-Marsden Dystonia Rating Scale-Motor score of 38.5% in the long term. We also report on 4 asymptomatic carriers, suggesting that some KMT2B mutations may be associated with incomplete disease penetrance.

CONCLUSIONS

KMT2B mutations are frequent in childhood-onset dystonia and cause a complex neurodevelopmental syndrome, often featuring growth retardation and intellectual disability as additional phenotypic features. A dramatic and long-lasting response to DBS is characteristic of DYT-KMT2B dystonia. © 2019 International Parkinson and Movement Disorder Society.

Novel mutations in KMT2B offer pathophysiological insights into childhood-onset progressive dystonia

Rapid progress has recently been made in the elucidation of the genetic basis of childhood-onset inherited generalized dystonia (IGD) due to the implementation of genomic sequencing methodologies. We identified four patients with childhood-onset IGD harboring novel disease-causing mutations in lysine-specific histone methyltransferase 2B gene (KMT2B) by whole-exome sequencing. The main focus of this paper is to gain novel pathophysiological insights through understanding the molecular consequences of these mutations. The disease course is mostly progressive, evolving from lower limbs into generalized dystonia, which could be associated with dysarthria, dysphonia, intellectual disability, orofacial dyskinesia, and sometimes distinct dysmorphic facial features. In two patients, motor performances improved after bilateral implantation of deep brain stimulation in the globus pallidus internus (GPi-DBS). Pharmacotherapy with trihexyphenidyl reduced dystonia in two patients. We discovered three novel KMT2B mutations. Our analyses revealed that the mutation in patient 1 (c.7463A > G, p.Y2488C) is localized in the highly conserved FYRC domain of KMT2B. This mutation holds the potential to alter the inter-domain FYR interactions, which could lead to KMT2B instability. The mutations in patients 2 and 3 (c.3596_3697insC, p.M1202Dfs*22; c.4229delA, p.Q1410Rfs*12) lead to predicted unstable transcripts, likely to be subject to degradation by non-sense-mediated decay. Childhood-onset progressive dystonia with orofacial involvement is one of the main clinical manifestations of KMT2B mutations. In all, 26% (18/69) of the reported cases have T2 signal alterations of the globus pallidus internus, mostly at a younger age. Anticholinergic medication and GPi-DBS are promising treatment options and shall be considered early.