Reviewing the Clinical Spectrum Related to Kmt2b Gene Mutations: Unusual Clinical Presentation and a Possible New Pathogenic Mutation

Introduction KMT2B related dystonia is a childhood onset generalized dystonia. Since its first description in 2016, different phenotypic spectrum have been reported. The aim of the case report is to provide data that may help to understand the spectrum of KMT2B-related disorders. We present two members of a family with a possible non-previously described pathogenic mutation and an unusual KMT2B related dystonia presentation: an adult onset and focal dystonia.Case Presentation The index patient is a 32 year-old woman with a generalized dystonia. Her maternal uncle presented a focal dystonia. Next-generation sequencing revealed a heterozygous missense mutation in KMT2B gene (19q13.12), described as a variant of uncertain significance (VUS). Although characteristic phenotype of KMT2B dystonia is a childhood onset generalized dystonia, different phenotypes have been related according to the kinds of mutations in this gene, also varying the age of symptom onset and the penetrance of the mutation. Asymptomatic or sub-clinical carriers and adult onset has been described. Due to the low prevalence of this variant in the general population and the low penetrance and high intrafamilial variability of this entity, we suggest that this mutation might be a pathogenic variant.ConclusionsKMT2B related dystonia is an emerging and prevalent monogenic dystonia whose incidence, genetic variability and clinical spectrum remain unknown. Despite the study of this gene is indicated in childhood onset dystonia, description of cases such as ours shows that its sequencing in patients with an adult-onset dystonia with family history can be useful for the diagnosis.

KMT2B-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.

Differential Deep Brain Stimulation Sites and Networks for Cervical vs. Generalized Dystonia

Dystonia is a debilitating disease with few conservative treatment options but many types of isolated dystonia can be effectively treated using deep brain stimulation (DBS) to the internal pallidum. While cervical and generalized forms of isolated dystonia have been targeted with a common approach to the posterior third of the nucleus, large-scale investigations between optimal stimulation sites and potential network effects in the two types of dystonia have not been carried out. Here, we retrospectively investigate clinical results following DBS for cervical and generalized dystonia in a multi-center cohort of 80 patients. We model DBS electrode placement based on pre- and postoperative imaging and introduce a novel approach to map optimal stimulation sites to anatomical space. Second, we analyse stimulation in context of a detailed pathway model of the subcortex to investigate the modulation of which tracts accounts for optimal clinical improvements. Third, we investigate stimulation in context of a broad-lense whole-brain functional connectome to illustrate potential multisynaptic network effects. Finally, we construct a joint model using local, tract- and network-based effects to explain variance in clinical outcomes in cervical and generalized dystonia. Our results show marked differences in optimal stimulation sites that map to the somatotopic structure of the internal pallidum. We further highlight that modulation of the pallidofugal main axis of the basal ganglia may be optimal for treatment of cervical dystonia, while pallidothalamic bundles account for effects in generalized dystonia. Finally, we show a common multisynaptic network substrate for both phenotypes in form of connectivity to cerebellum and somatomotor cortex. Our results suggest a multi-level model that could account for effectivity of treatment in cervical and generalized dystonia and could potentially help guide DBS programming and surgery, in the future.

Dystonia in children

Dystonia is a motor disorder characterized by sustained muscle contractions producing twisting, repetitive, and patterned movements or abnormal postures. Dystonia is among the most commonly observed motor disorders in clinical practice in children. Unlike dystonia in adults that typically remains focal or spreads only to nearby muscle groups, childhood dystonia often generalizes. Classification of dystonia has direct implications for narrowing down the differential diagnosis, choosing the diagnostic work-up, predicting the prognosis, and choosing treatment options. The etiology of pediatric dystonia is quite heterogeneous. The etiological classification distinguishes primary dystonia with no identifiable exogenous cause or evidence of neurodegeneration and secondary syndromes. Dystonia can be secondary to any pathological process that affects the basal ganglia. The treatment options of childhood dystonia include several oral pharmaceutical agents, botulinum toxin injections, and deep brain stimulation therapy. Botulinum toxin treatment is the first choice treatment for most types of focal dystonia. In children it is less used because dystonic forms are mainly generalized, but it might also be helpful in controlling the most disabling symptoms of segmental or generalized dystonia. Long-term electrical stimulation of the globus pallidum internum is now established as an effective treatment for various types of movement disorders including dystonia. However, this method has not yet found its application in Russia due to the difficulty of implementation and the lack of patient routing. To increase the effectiveness of complex therapy of dystonia in children, new pathogenetic methods of treatment of common forms of primary dystonia and dystonic syndromes in the structure of degenerative diseases of the central nervous system are needed, as well as the development of optimal algorithms for the diagnosis and treatment of these patients.