Treatable Inherited Movement Disorders in Children: Spotlight on Clinical and Biochemical Features

Severe Acute Motor Exacerbations (SAME) across Metabolic, Developmental and Genetic Disorders

Acute presentation of severe motor disorders is a diagnostic and management challenge. We define severe acute motor exacerbations (SAME) as acute/subacute motor symptoms that persist for hours-to-days with a severity that compromise vital signs (temperature, breath, and heart rate) and bulbar function (swallowing/dysphagia). Phenomenology includes dystonia, choreoathetosis, combined movement disorders, weakness, and hemiplegic attacks. SAME can develop in diverse diseases and can be preceded by triggers or catabolic states. Recent descriptions of SAME in complex neurodevelopmental and epileptic encephalopathies have broadened appreciation of this presentation beyond inborn errors of metabolism. A high degree of clinical suspicion is required to identify appropriately targeted investigations and management. We conducted a comprehensive literature analysis of etiologies. Reported triggers are described and classified as per pathophysiological mechanism. A video of six cases displaying multiple SAME with diverse outcomes is provided. We identified 50 different conditions that manifest SAME, some associated with developmental regression. Etiologies include disorders of metabolism: energy substrate, amino acids, complex molecules, vitamins/cofactors, minerals, and neurotransmitters/synaptic vesicle cycling. Non-metabolic neurodegenerative and genetic disorders that present with movement disorders and epilepsy can additionally manifest SAME. A limited number of triggers are grouped here, together with an approach to investigations and general management strategies. Several neurogenetic and neurometabolic disorders manifest SAME. Identifying triggers can help in certain cases narrow the differential diagnosis and guide the expeditious application of targeted therapies to minimize adverse developmental and neurological consequences. This process may inform pathogenesis and eventually improve our understanding of the mechanisms that lead to the development of SAME. © 2024 International Parkinson and Movement Disorder Society.

Childhood Neurological Disorders With Hyperhomocystinemia: A Case-Based Review

Hyperhomocysteinemia is a rare neurometabolic syndrome with diverse manifestations in the pediatric age group, thereby posing a diagnostic challenge. Biochemical testing is imperative to guide plan of evaluation, which may include appropriate genetic testing, in inherited disorders. Through this case-based approach, we demonstrate the heterogeneity of clinical presentation, biochemical and genetic evaluation, and treatment strategies that may reverse this condition among children.

Surgical treatment of movement disorders in neurometabolic conditions

Refractory movement disorders are a common feature of inborn errors of metabolism (IEMs), significantly impacting quality of life and potentially leading to life-threatening complications such as status dystonicus. Surgical techniques, including deep brain stimulation (DBS) and lesioning techniques, represent an additional treatment option. However, the application and benefits of these procedures in neurometabolic conditions is not well understood. This results in challenges selecting surgical candidates and counseling patients preoperatively. In this review, we explore the literature of surgical techniques for the treatment of movement disorders in IEMs. Globus pallidus internus DBS has emerged as a beneficial treatment option for dystonia in Panthotate-Kinase-associated Neurodegeneration. Additionally, several patients with Lesch-Nyhan Disease have shown improvement following pallidal stimulation, with more robust effects on self-injurious behavior than dystonia. Although there are numerous reports describing benefits of DBS for movement disorders in other IEMs, the sample sizes have generally been small, limiting meaningful conclusions. Currently, DBS is preferred to lesioning techniques. However, successful use of pallidotomy and thalamotomy in neurometabolic conditions has been reported and may have a role in selected patients. Surgical techniques have also been used successfully in patients with IEMs to treat status dystonicus. Advancing our knowledge of these treatment options could significantly improve the care for patients with neurometabolic conditions.

Neurophysiological assessment of juvenile parkinsonism due to primary monoamine neurotransmitter disorders

No studies have investigated voluntary movement abnormalities and their neurophysiological correlates in patients with parkinsonism due to inherited primary monoamine neurotransmitter (NT) disorders. Nine NT disorders patients and 16 healthy controls (HCs) were enrolled. Objective measurements of repetitive finger tapping were obtained using a motion analysis system. Primary motor cortex (M1) excitability was assessed by recording the input/output (I/O) curve of motor-evoked potentials (MEP) and using a conditioning test paradigm for short-interval intracortical inhibition (SICI) assessment. M1 plasticity-like mechanisms were indexed according to MEPs amplitude changes after the paired associative stimulation protocol. Patient values were considered abnormal if they were greater or lower than two standard deviations from the average HCs value. Patients with aromatic amino acid decarboxylase, tyrosine hydroxylase, and 6-pyruvoyl-tetrahydropterin synthase defects showed markedly reduced velocity (5/5 patients), reduced movement amplitude, and irregular rhythm (4/5 patients). Conversely, only 1 out of 3 patients with autosomal-dominant GTPCH deficiency showed abnormal movement parameters. Interestingly, none of the patients had a progressive reduction in movement amplitude or velocity during the tapping sequence (no sequence effect). Reduced SICI was the most prominent neurophysiological abnormality in patients (5/9 patients). Finally, the I/O curve slope correlated with movement velocity and rhythm in patients. We provided an objective assessment of finger tapping abnormalities in monoamine NT disorders. We also demonstrated M1 excitability changes possibly related to alterations in motor execution. Our results may contribute to a better understanding of the pathophysiology of juvenile parkinsonism due to dopamine deficiency.

Shedding light on the phenotypic–genotypic correlation of rare treatable and potentially treatable pediatric movement disorders

Background

Advances in genetic science have led to the identification of many rare treatable pediatric movements disorders (MDs). We explored the phenotypic–genotypic spectrum of pediatric patients presenting with MDs. By this, we aimed at raising awareness about such rare disorders, especially in our region. Over the past 3 years, we reviewed the demographic data, clinical profile, molecular genetics and other diagnostic workups of pediatric patients presenting with MDs.

Results

Twelve patients were identified; however, only six patients were genetically confirmed. The phenomenology of MDs ranged from paroxysmal kinesigenic choreoathetosis (1 patient), exercise-induced dyskinesia (2 patients), ataxia (2 patients) and dystonia (2 patients). Whole-exome sequencing in addition to the functional studies for some patients revealed a specific genetic diagnosis being responsible for their MDs. The genetic diagnosis of our patients included infantile convulsions and paroxysmal choreoathetosis syndrome and episodic ataxia due to “pathogenic homozygous mutation of PRRT2 gene,” glucose transporter type 1 deficiency-exercise induced dyskinesia due to “De Novo pathogenic heterozygous missense mutation of exon 4 of SLC2A1 gene,” aromatic L amino acid decarboxylase deficiency due to “pathogenic homozygous mutation of the DDC gene,” myopathy with extrapyramidal signs due to “likely pathogenic homozygous mutations of the MICU1 gene,” mitochondrial trifunctional protein deficiency due to “homozygous variant of uncertain significance (VUS) of HADHB gene” and glutaric aciduria II with serine deficiency due to “homozygous VUS for both ETFDH and PHGDH genes.” After receiving the treatment as per recognized treatment protocols, two patients showed complete resolution of symptoms and the rest showed variable responses.

Conclusion

Identifying the genetic etiology of our patients guided us to provide either disease-specific treatment or redirected our management plan. Hence, highlighting the value of molecular genetic analysis to avoid the diagnostic odyssey and identify treatable MDs.

Stroke and stroke-like episodes in inborn errors of metabolism: Pathophysiological and clinical implications

Inborn errors of metabolism causing stroke (ischemic or haemorrhagic) or stroke-like episodes (e.g., that are also called "metabolic strokes" and include acute brain lesions not related with alterations of blood flow) cover a wide range of diseases in which acute metabolic decompensations after trigger events (e.g., fever, dehydration, sepsis etc.) may have a variable frequency. The early diagnosis of these conditions is essential because, despite their rarity, effective symptomatic treatments may be available for acute settings (e.g., arginine for Mitochondrial myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes- MELAS) while in other cases disease modifying therapies may be useful to prevent stroke occurrence, recurrence, or relapse (e.g., Fabry disease). The detection of a non-vascular distribution of lesions and the diffuse use of ¹HMRS are often diriment in the differential of ischemic and metabolic strokes. This review summarized the main clinical features and the pathophysiological mechanisms of stroke and stroke-like episodes in inborn errors of metabolism presenting with stroke as part of natural history of the disease. These conditions belong to different etiological groups, such as organic acidurias, mitochondrial encephalopathies, homocystinuria and remethylation disorders, urea cycle disorders, lysosomal diseases (e.g. Fabry disease, glycogen storage disease), congenital disorders of glycosylation, neurotransmitter disorders, adenosine deaminase 2 deficiency and few other neurometabolic disorders.

Acute Movement Disorders in Childhood

Acute-onset movement disorders (MDs) are an increasingly recognized neurological emergency in both adults and children. The spectrum of possible causes is wide, and diagnostic work-up is challenging. In their acute presentation, MDs may represent the prominent symptom or an important diagnostic clue in a broader constellation of neurological and extraneurological signs. The diagnostic approach relies on the definition of the overall clinical syndrome and on the recognition of the prominent MD phenomenology. The recognition of the underlying disorder is crucial since many causes are treatable. In this review, we summarize common and uncommon causes of acute-onset movement disorders, focusing on clinical presentation and appropriate diagnostic investigations. Both acquired (immune-mediated, infectious, vascular, toxic, metabolic) and genetic disorders causing acute MDs are reviewed, in order to provide a useful clinician’s guide to this expanding field of pediatric neurology.

Pediatric Paroxysmal Exercise-Induced Neurological Symptoms: Clinical Spectrum and Diagnostic Algorithm

Paroxysmal exercise-induced neurological symptoms (PENS) encompass a wide spectrum of clinical phenomena commonly presenting during childhood and characteristically elicited by physical exercise. Interestingly, few shared pathogenetic mechanisms have been identified beyond the well-known entity of paroxysmal exercise-induced dyskinesia, PENS could be part of more complex phenotypes including neuromuscular, neurodegenerative, and neurometabolic disease, epilepsies, and psychogenetic disorders. The wide and partially overlapping phenotypes and the genetic heterogeneity make the differential diagnosis frequently difficult and delayed; however, since some of these disorders may be treatable, a prompt diagnosis is mandatory. Therefore, an accurate characterization of these symptoms is pivotal for orienting more targeted biochemical, radiological, neurophysiological, and genetic investigations and finally treatment. In this article, we review the clinical, genetic, pathophysiologic, and therapeutic landscape of paroxysmal exercise induced neurological symptoms, focusing on phenomenology and differential diagnosis.

Movement disorders in primary central nervous system lymphoma: two unreported cases and a review of literature

BACKGROUND

Recognition of secondary movement disorders (SMDs) is fundamental either to alleviate disabling disturbances or to treat potentially life-threatening conditions, such as brain tumors. Primary CNS lymphoma (PCNSL) is a rare form of CNS cancer that is often located in subcortical areas, accounting for both neuropsychiatric and motoric disorders. Nevertheless, an overview on PCNSL-related movement disorders (MDs) phenomenology has not been provided yet.

OBJECTIVE

To outline the main features of PCNSL-related MDs.

METHODS

A retrospective analysis was conducted on a cohort of patients with PCNSL presenting with MDs, including all existing cases identified by a systematic literature review (source: Medline; period: 1946-2020) and two unreported cases. Data on phenomenology, neuroimaging, histology, and clinical course were collected.

RESULTS

A total cohort of fifteen subjects was defined, enrolling thirteen previously described patients extracted from eleven published studies, and our two unreported cases. A parkinsonian syndrome appearing at about 60 years of age, unresponsive to levodopa, associated to other neurological signs, resulted as the most common presentation of PCNSL-related MD. Chorea, dystonia, and dyskinesia occurred less frequently, with some degree of responsiveness to symptomatic treatments. Basal ganglia were involved in most cases and motoric disturbances often ameliorated after tumor mass reduction.

CONCLUSIONS

This study identified those features of PCNSL-related MDs that could support an appropriate approach to such a rare condition. In fact, while the outcome remains still poor, the therapeutic scenario of PCNSL is changing; an early diagnosis together with an adequate management will be thus crucial for timely and successful interventions.

Parkinsonism in children: Clinical classification and etiological spectrum

Infantile- and childhood-onset parkinsonism is mainly due to genetic alterations and is an exceedingly rare condition, unlike Parkinson's disease (PD), which is one of the most common neurologic disorders in adulthood. The clinical characterization of parkinsonism during early stages of neuromotor development is controversial due to the lack of consensus regarding the clinical criteria of PD or parkinsonism in the immature brain. The classification here proposed is based on a review of conditions that emerge during infancy and childhood, with key symptoms evocative of adult parkinsonism. The proposed nosography is based on age at presentation, clinical features, outcome, and etiological background. It includes developmental parkinsonism, infantile degenerative parkinsonism, parkinsonism in the setting of neurodevelopmental disorders, parkinsonism in the setting of multisystem brain diseases, juvenile parkinsonism and dystonia-parkinsonism, and acquired parkinsonism. The subgroups denoting peculiar clinical presentations as a consequence of disease impact on the immature brain are developmental parkinsonism due to monoamine metabolic disorders and infantile degenerative parkinsonism caused by DAT and WASR2 defects. More tardive parkinsonisms occur in genetic conditions that cause a generalized derangement of neurodevelopmental processes, such as those due to MECP2, NR4A2, SCN1A, and RAB39B. Some conditions presenting with neurodevelopmental disorder can progress later, disclosing their neurodegenerative nature (i.e. WDR45 and KCND3). Finally, new emerging conditions with childhood-onset parkinsonism arise from the cumulative effect of multiple genetic lesions.

Clinical and Genetic Overview of Paroxysmal Movement Disorders and Episodic Ataxias

Paroxysmal movement disorders (PMDs) are rare neurological diseases typically manifesting with intermittent attacks of abnormal involuntary movements. Two main categories of PMDs are recognized based on the phenomenology: Paroxysmal dyskinesias (PxDs) are characterized by transient episodes hyperkinetic movement disorders, while attacks of cerebellar dysfunction are the hallmark of episodic ataxias (EAs). From an etiological point of view, both primary (genetic) and secondary (acquired) causes of PMDs are known. Recognition and diagnosis of PMDs is based on personal and familial medical history, physical examination, detailed reconstruction of ictal phenomenology, neuroimaging, and genetic analysis. Neurophysiological or laboratory tests are reserved for selected cases. Genetic knowledge of PMDs has been largely incremented by the advent of next generation sequencing (NGS) methodologies. The wide number of genes involved in the pathogenesis of PMDs reflects a high complexity of molecular bases of neurotransmission in cerebellar and basal ganglia circuits. In consideration of the broad genetic and phenotypic heterogeneity, a NGS approach by targeted panel for movement disorders, clinical or whole exome sequencing should be preferred, whenever possible, to a single gene approach, in order to increase diagnostic rate. This review is focused on clinical and genetic features of PMDs with the aim to (1) help clinicians to recognize, diagnose and treat patients with PMDs as well as to (2) provide an overview of genes and molecular mechanisms underlying these intriguing neurogenetic disorders.