Adult-onset KMT2B-related dystonia

Bi-pallidal deep brain stimulation as an effective therapy in atypical two-stage evolution adult-onset KMT2B-related dystonia

We report an adult-onset KMT2B-related dystonia with a two-stage evolution: focal cervical onset followed by rapid generalization. Whole genome sequencing identified a likely pathogenic KMT2B variant. Bi-pallidal deep brain stimulation led to an 83% motor improvement, highlighting its therapeutic potential in late-onset atypical two-stage evolution KMT2B-dystonia.

Clinical Presentation of KMT2B-Related Dystonia: A Case Report

This case presents an eight-year-old boy who visited the clinic with complaints of worsening gait and dystonic movements. The patient had asymmetric spasticity in all extremities, which was more pronounced on the right side. The diagnosis of KMT2B-related dystonia was made. KMT2B-related dystonia is a generalized dystonia of childhood-onset that typically begins in the lower limbs, gradually progressing upward and leading to generalized dystonia. The patient had prominent, involuntary hand movements, mainly on the right side, and difficulties with fine motor function. These symptoms severely impacted his ability to engage in routine tasks and daily activities. Currently, he is undergoing multidisciplinary rehabilitation treatment at the Neurodevelopment Center to enhance his functional abilities and participation and to improve his overall quality of life. Given its relative rarity in clinical practice, this case underscores the importance of early recognition and thorough documentation of KMT2B-related dystonia. By increasing awareness of this condition, healthcare providers can facilitate timely diagnosis and implement more effective treatment strategies. Early intervention can significantly improve outcomes and support children with this challenging disorder in leading fulfilling lives.

[Phenotypic and genotypic spectrum of KMT2B dystonia. Description of three Colombian patients]

INTRODUCTION

KMT2B-related dystonia is a childhood-onset movement disorder characterized by focal dystonia of the lower extremities progressing to generalized dystonia with predominant cervical, cranial, and laryngeal involvement. So far, fewer than 100 variants have been reported, the vast majority being de novo mutations. The presenting frame of KMT2B dystonia, with dysmorphology features and other complex neurologic symptoms shows the spectrum of KMT2B dystonia as a probable syndromic disease, rather than an isolated early-onset dystonia, which has been the classic view of the condition.

CASE REPORTS

We report three patients who presented regression in their neurodevelopment, focal dystonia of the lower limbs with subsequent generalization, in whom two de novo variants were reported in the KMT2B gene, with a mean age of presentation lower than the average reported worldwide.

CONCLUSIONS

We describe the largest local series of patients with KMT2B dystonia in Colombia (to our knowledge), which allows us to expand the genotype-phenotype relationship of this genetic dystonia. Although many affected individuals follow a similar disease course, it is important to determine clinical features that may be associated such as neurodevelopmental regression.

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.

Early-onset inherited dystonias versus late-onset idiopathic dystonias: Same or different biological mechanisms?

Dystonia syndromes encompass a heterogeneous group of movement disorders which might be differentiated by several clinical-historical features. Among the latter, age-at-onset is probably the most important in predicting the likelihood both for the symptoms to spread from focal to generalized and for a genetic cause to be found. Accordingly, dystonia syndromes are generally stratified into early-onset and late-onset forms, the former having a greater likelihood of being monogenic disorders and the latter to be possibly multifactorial diseases, despite being currently labeled as idiopathic. Nonetheless, there are several similarities between these two groups of dystonia, including shared pathophysiological and biological mechanisms. Moreover, there is also initial evidence of age-related modifiers of early-onset dystonia syndromes and of critical periods of vulnerability of the sensorimotor network, during which a combination of genetic and non-genetic insults is more likely to produce symptoms. Based on these lines of evidence, we reappraise the double-hit hypothesis of dystonia, which would accommodate both similarities and differences between early-onset and late-onset dystonia in a single framework.