Protein mutated in paroxysmal dyskinesia interacts with the active zone protein RIM and suppresses synaptic vesicle exocytosis

Prognostic Values of Core Genes in Pilocytic Astrocytom

BACKGROUND

Pilocytic astrocytoma (PA) is the most common primary brain tumor in children and adolescents. Treatment strategy largely depends on its key genes and molecular mutations. This study aimed to identify potential biomarkers of PA closely related to its prognosis.

METHODS

The gene expression profiles (series numbers GSE50161, GSE66354, and GSE86574) of PA and normal brain tissues were downloaded from the Gene Expression Omnibus database. The Gene Expression Omnibus2R was used to identify differentially expressed genes. The overlapping differentially expressed genes were subjected to Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses using the Database for Annotation, Visualization, and Integrated Discovery (DAVID) database. A protein-protein interaction network was constructed using Search Tool for the Retrieval of Interacting Genes (STRING) and Cytoscape. The Gene Expression Profiling Interactive Analysis 2 (GEPIA2) tool analyzed the impact of hub genes on PA prognosis based on the Kaplan-Meier curves.

RESULTS

Compared with normal brain tissues (n = 36), a total of 37 upregulated and 144 downregulated genes were identified in PA (n = 40). In the protein-protein interaction network construction and GEPIA2 survival analysis, 2 of the top 10 hub genes were significantly associated with decreased overall survival of PA patients, namely Gamma-aminobutyric acid A receptor alpha 2 (hazard ratio  =  2.8, P  <  0.01) and regulating synaptic membrane exocytosis protein 1) (hazard ratio =  3.2, P  <  0.01).

CONCLUSIONS

This bioinformatics analysis reveals that low expression of Gamma-aminobutyric acid A receptor alpha 2 and regulating synaptic membrane exocytosis protein 1 is associated with a favorable prognosis for PA patients. These 2 hub genes could be novel biomarkers for prognosis assessment, furthermore a key element for treatment decisions in the future.

Paroxysmal movement disorders: Paroxysmal dyskinesia and episodic ataxia

Paroxysmal movement disorders have traditionally been classified into paroxysmal dyskinesia (PxD), which consists in attacks of involuntary movements (mainly dystonia and/or chorea) without loss of consciousness, and episodic ataxia (EA), which features spells of cerebellar dysfunction with or without interictal neurological manifestations. In this chapter, PxD will be discussed first according to the trigger-based classification, thus reviewing clinical, genetic, and molecular features of paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, and paroxysmal exercise-induced dyskinesia. EA will be presented thereafter according to their designated gene or genetic locus. Clinicogenetic similarities among paroxysmal movement disorders have progressively emerged, which are herein highlighted along with growing evidence that their pathomechanisms overlap those of epilepsy and migraine. Advances in our comprehension of the biological pathways underlying paroxysmal movement disorders, which involve ion channels as well as proteins associated with the vesical synaptic cycle or implicated in neuronal energy metabolism, may represent the cornerstone for defining a shared pathophysiologic framework and developing target-specific therapies.

Study of variants in genes implicated in rare familial migraine syndromes and their association with migraine in 200,000 exome-sequenced UK Biobank participants

BACKGROUND

A number of genes have been implicated in rare familial syndromes which have migraine as part of their phenotype but these genes have not previously been implicated in the common form of migraine.

METHODS

Among exome-sequenced participants in the UK Biobank, we identified 7194 migraine cases with the remaining 193,433 participants classified as controls. We investigated rare variants in 10 genes previously reported to be implicated in conditions with migraine as a prominent part of the phenotype and carried out gene- and variant-based tests for association.

RESULTS

We found no evidence for association of these genes or variants with the common form of migraine seen in our subjects. In particular, a frameshift variant in KCNK18, p.(Phe139Trpfs*24), which had been shown to segregate with migraine with aura in a multiply affected pedigree, was found in 196 (0.10%) controls as well as in 10 (0.14%) cases (χ²  = 0.96, 1 df, p = 0.33).

CONCLUSIONS

Since there is no other reported evidence to implicate KCNK18, we conclude that this gene and its product, TRESK, should no longer be regarded as being involved in migraine aetiology. Overall, we do not find that rare, functional variants in genes previously implicated to be involved in familial syndromes including migraine as part of the phenotype make a contribution to the commoner forms of migraine observed in this population.

Molecular signatures underlying neurofibrillary tangle susceptibility in Alzheimer's disease

Tau aggregation in neurofibrillary tangles (NFTs) is closely associated with neurodegeneration and cognitive decline in Alzheimer's disease (AD). However, the molecular signatures that distinguish between aggregation-prone and aggregation-resistant cell states are unknown. We developed methods for the high-throughput isolation and transcriptome profiling of single somas with NFTs from the human AD brain, quantified the susceptibility of 20 neocortical subtypes for NFT formation and death, and identified both shared and cell-type-specific signatures. NFT-bearing neurons shared a marked upregulation of synaptic transmission-related genes, including a core set of 63 genes enriched for synaptic vesicle cycling. Oxidative phosphorylation and mitochondrial dysfunction were highly cell-type dependent. Apoptosis was only modestly enriched, and the susceptibilities of NFT-bearing and NFT-free neurons for death were highly similar. Our analysis suggests that NFTs represent cell-type-specific responses to stress and synaptic dysfunction. We provide a resource for biomarker discovery and the investigation of tau-dependent and tau-independent mechanisms of neurodegeneration.

Preliminary study on pathogenic mechanism of first Chinese family with PNKD

Background

The first Chinese family with paroxysmal non-kinesigenic dystonia (PNKD) was confirmed to harbour a PNKD mutation. However, the pathogenic mechanism of the PNKD-causing gene mutation was unclear.

Methods

Wild-type and mutant PNKD-L plasmids were prepared and transfected into the C6 cell line to study the distribution and stability of PNKD protein in C6 cells and its effect on the glutathione content. The blood and cerebrospinal fluid (CSF) of 3 PNKD patients and 3 healthy controls were collected. The differentially expressed proteins were identified using isobaric tags for relative and absolute quantitation. Furthermore, Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analyses were performed, and the protein–protein interaction network was constructed.

Results

Wild-type PNKD protein was mainly distributed in the membranes, whereas mutant PNKD protein was distributed throughout the C6 cells. After transfection with mutant PNKD-L plasmid, the glutathione content decreased significantly in C6 cells; the stability of the mutant PNKD protein was significantly low. There were 172 and 163 differentially expressed proteins in CSF and plasma, respectively, of PNKD patients and healthy controls. For these proteins, blood microparticle and complex activation (classical pathway) were the common GO enrichment term, and complex and coordination cascade pathway were the common KEGG enrichment pathway. Recombinant mothers against decapentaplegic homolog 4 (SMAD4) was one of the differentially expressed proteins; it exhibited a relationship with the aforementioned enrichment GO terms and KEGG pathway.

Conclusion

PNKD protein was mainly distributed in cell membranes. PNKD-L mutation affected subcellular localisation, PNKD protein stability, and glutathione content. SMAD4 was found to be a potential biomarker for PNKD diagnosis.

Metabolic Shades of S-D-Lactoylglutathione

S-D-lactoylglutathione (SDL) is an intermediate of the glutathione-dependent metabolism of methylglyoxal (MGO) by glyoxalases. MGO is an electrophilic compound that is inevitably produced in conjunction with glucose breakdown and is essentially metabolized via the glyoxalase route. In the last decades, MGO metabolism and its cytotoxic effects have been under active investigation, while almost nothing is known about SDL. This article seeks to fill the gap by presenting an overview of the chemistry, biochemistry, physiological role and clinical importance of SDL. The effects of intracellular SDL are investigated in three main directions: as a substrate for post-translational protein modifications, as a reservoir for mitochondrial reduced glutathione and as an energy currency. In essence, all three approaches point to one direction, namely, a metabolism-related regulatory role, enhancing the cellular defense against insults. It is also suggested that an increased plasma concentration of SDL or its metabolites may possibly serve as marker molecules in hemolytic states, particularly when the cause of hemolysis is a disturbance of the pay-off phase of the glycolytic chain. Finally, SDL could also represent a useful marker in such metabolic disorders as diabetes mellitus or ketotic states, in which its formation is expected to be enhanced. Despite the lack of clear-cut evidence underlying the clinical and experimental findings, the investigation of SDL metabolism is a promising field of research.

Paroxysmal dyskinesia and electrodermal volatility: The role of mindfulness, self-compassion and psychophysiological interventions

To date, there are no behavioral or psychophysiological treatment studies on paroxysmal dyskinesia (PD). PD is a group of debilitating movement disorders that present with severe episodes of dystonia, chorea, and/or ballistic like movements. This is a first case report of a 50-year-old male who received behavioral interventions (e.g., mindfulness, CBT, and biofeedback interventions) to manage his PD episodes in tandem with multidisciplinary treatments (e.g., neurology, psychiatry, etc.). The paper primarily discusses the serendipitous observation of galvanic skin response (GSR) elevations and spikes immediately before and after the onset of PD episodes. GSR volatility was noted in wave amplitude and wave morphology. Graphs are presented to illustrate GSR volatility associate with PD episodes and the reduction of GSR volatility in response to behavioral approaches. The discussion highlights the feasibility of using GSR biofeedback as an adjunct to mindfulness and CBT to manage PD as part of a multidisciplinary treatment approach. Peripherally, issues that related to misclassification of somatic symptoms and related disorders (e.g., psychogenic non-epileptic seizures) and aspects of neurocognitive disorders are discussed. The paper reviews neurological findings, MRI, neuropsychological data, and psychiatric assessment to highlight the dilemma clinician's face and clarify behavioral practices to further the management of PD.

Striatal Indirect Pathway Dysfunction Underlies Motor Deficits in a Mouse Model of Paroxysmal Dyskinesia

Abnormal involuntary movements, or dyskinesias, are seen in many neurologic diseases, including disorders where the brain appears grossly normal. This observation suggests that alterations in neural activity or connectivity may underlie dyskinesias. One influential model proposes that involuntary movements are driven by an imbalance in the activity of striatal direct and indirect pathway neurons (dMSNs and iMSNs, respectively). Indeed, in some animal models, there is evidence that dMSN hyperactivity contributes to dyskinesia. Given the many diseases associated with dyskinesia, it is unclear whether these findings generalize to all forms. Here, we used male and female mice in a mouse model of paroxysmal nonkinesigenic dyskinesia (PNKD) to assess whether involuntary movements are related to aberrant activity in the striatal direct and indirect pathways. In this model, as in the human disorder PNKD, animals experience dyskinetic attacks in response to caffeine or alcohol. Using optically identified striatal single-unit recordings in freely moving PNKD mice, we found a loss of iMSN firing during dyskinesia bouts. Further, chemogenetic inhibition of iMSNs triggered dyskinetic episodes in PNKD mice. Finally, we found that these decreases in iMSN firing are likely because of aberrant endocannabinoid-mediated suppression of glutamatergic inputs. These data show that striatal iMSN dysfunction contributes to the etiology of dyskinesia in PNKD, and suggest that indirect pathway hypoactivity may be a key mechanism for the generation of involuntary movements in other disorders.SIGNIFICANCE STATEMENT Involuntary movements, or dyskinesias, are part of many inherited and acquired neurologic syndromes. There are few effective treatments, most of which have significant side effects. Better understanding of which cells and patterns of activity cause dyskinetic movements might inform the development of new neuromodulatory treatments. In this study, we used a mouse model of an inherited human form of paroxysmal dyskinesia in combination with cell type-specific tools to monitor and manipulate striatal activity. We were able to narrow in on a specific group of neurons that causes dyskinesia in this model, and found alterations in a well-known form of plasticity in this cell type, endocannabinoid-dependent synaptic LTD. These findings point to new areas for therapeutic development.

PRRT2 modulates presynaptic Ca2+ influx by interacting with P/Q-type channels

Loss-of-function mutations in proline-rich transmembrane protein-2 (PRRT2) cause paroxysmal disorders associated with defective Ca2+ dependence of glutamatergic transmission. We find that either acute or constitutive PRRT2 deletion induces a significant decrease in the amplitude of evoked excitatory postsynaptic currents (eEPSCs) that is insensitive to extracellular Ca2+ and associated with a reduced contribution of P/Q-type Ca2+ channels to the EPSC amplitude. This synaptic phenotype parallels a decrease in somatic P/Q-type Ca2+ currents due to a decreased membrane targeting of the channel with unchanged total expression levels. Co-immunoprecipitation, pull-down assays, and proteomics reveal a specific and direct interaction of PRRT2 with P/Q-type Ca2+ channels. At presynaptic terminals lacking PRRT2, P/Q-type Ca2+ channels reduce their clustering at the active zone, with a corresponding decrease in the P/Q-dependent presynaptic Ca2+ signal. The data highlight the central role of PRRT2 in ensuring the physiological Ca2+ sensitivity of the release machinery at glutamatergic synapses.

Genetic updates on paroxysmal dyskinesias

The paroxysmal dyskinesias are a diverse group of genetic disorders that manifest as episodic movements, with specific triggers, attack frequency, and duration. With recent advances in genetic sequencing, the number of genetic variants associated with paroxysmal dyskinesia has dramatically increased, and it is now evident that there is significant genotype-phenotype overlap, reduced (or incomplete) penetrance, and phenotypic variability. In addition, a variety of genetic conditions can present with paroxysmal dyskinesia as the initial symptom. This review will cover the 34 genes implicated to date and propose a diagnostic workflow featuring judicious use of whole-exome or -genome sequencing. The goal of this review is to provide a common understanding of paroxysmal dyskinesias so basic scientists, geneticists, and clinicians can collaborate effectively to provide diagnoses and treatments for patients.

Biallelic variants in TSPOAP1, encoding the active-zone protein RIMBP1, cause autosomal recessive dystonia

Dystonia is a debilitating hyperkinetic movement disorder, which can be transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense, and missense variants in TSPOAP1, which encodes the active-zone RIM-binding protein 1 (RIMBP1), as a genetic cause of autosomal recessive dystonia in 7 subjects from 3 unrelated families. Subjects carrying loss-of-function variants presented with juvenile-onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between dysfunction of the presynaptic active zone and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

A genome-wide analysis of cardiac lesions of pigs that die during transport: Is heart failure of in-transit-loss pigs associated with a heritable cardiomyopathy?

While heart failure is a primary cause of death for many in-transit-loss (ITL) pigs, the underlying cause of these deaths is not known. Cardiomyopathies are considered a common cause of heart failure in humans and often have a genetic component. The objective of this study was to determine if genes associated with cardiomyopathies could be identified in ITL pigs. Samples from the hearts of pigs that died during transport to an abattoir in Ontario, Canada were collected and genotyped along with samples from pigs that did not die during transport (ILT hearts: n = 149; non-ITL/control hearts: n = 387). Genome-wide analyses were carried out on each of the determined phenotypes (gross cardiac lesions) using a medium density single nucleotide polymorphism (SNP) chip and 500 kb windows/regions for analysis, with 250 kb regions of overlap. The distribution derived by a multidimensional scaling (MDS) analysis of all phenotypes demonstrated a lack of complete separation between phenotypes of affected and unaffected animals, which made diagnosis difficult. Although genetic differences were small, a few genes associated with dilated cardiomyopathy (DCM) and arrhythmogenic right ventricular cardiomyopathy (ARVM) were identified. In addition, multiple genes associated with cardiac arrhythmias and ventricular hypertrophy were identified that can possibly result in heart failure. The results of this preliminary study did not provide convincing evidence that a single, heritable cardiomyopathy is the cause of heart failure in ITL pigs.

Paroxysmal Genetic Movement Disorders and Epilepsy

Paroxysmal movement disorders include paroxysmal kinesigenic dyskinesia, paroxysmal non-kinesigenic dyskinesia, paroxysmal exercise-induced dyskinesia, and episodic ataxias. In recent years, there has been renewed interest and recognition of these disorders and their intersection with epilepsy, at the molecular and pathophysiological levels. In this review, we discuss how these distinct phenotypes were constructed from a historical perspective and discuss how they are currently coalescing into established genetic etiologies with extensive pleiotropy, emphasizing clinical phenotyping important for diagnosis and for interpreting results from genetic testing. We discuss insights on the pathophysiology of select disorders and describe shared mechanisms that overlap treatment principles in some of these disorders. In the near future, it is likely that a growing number of genes will be described associating movement disorders and epilepsy, in parallel with improved understanding of disease mechanisms leading to more effective treatments.

Increased responsiveness at the cerebellar input stage in the PRRT2 knockout model of paroxysmal kinesigenic dyskinesia

PRoline-Rich Transmembrane protein-2 (PRRT2) is a recently described neuron-specific type-2 integral membrane protein with a large cytosolic N-terminal domain that distributes in presynaptic and axonal domains where it interacts with several presynaptic proteins and voltage-gated Na⁺ channels. Several PRRT2 mutations are the main cause of a wide and heterogeneous spectrum of paroxysmal disorders with a loss-of-function pathomechanism. The highest expression levels of PRRT2 in brain occurs in cerebellar granule cells (GCs) and cerebellar dysfunctions participate in the dyskinetic phenotype of PRRT2 knockout (KO) mice. We have investigated the effects of PRRT2 deficiency on the intrinsic excitability of GCs and the input-output relationships at the mossy fiber-GC synapses. We show that PRRT2 KO primary GCs display increased expression of Na⁺ channels, increased amplitude of Na⁺ currents and increased length of the axon initial segment, leading to an overall enhancement of intrinsic excitability. In acute PRRT2 KO cerebellar slices, GCs were more prone to action potential discharge in response to mossy fiber activation and exhibited an enhancement of transient and persistent Na⁺ currents, in the absence of changes at the mossy fiber-GC synapses. The results support a key role of PRRT2 expressed in GCs in the physiological regulation of the excitatory input to the cerebellum and are consistent with a major role of a cerebellar dysfunction in the pathogenesis of the PRRT2-linked paroxysmal pathologies.

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.

Migraine pathways and the identification of novel therapeutic targets

Introduction: Migraine is a chronic neurovascular disorder characterized by recurrent headache attacks associated with neurological and autonomic symptoms. The pathophysiological mechanisms of the disease are extremely complex, involving hypothalamic and trigeminovascular activation, cortical spreading depression, release of pro-inflammatory peptides, peripheral and central sensitization. The underlying cellular and molecular mechanisms have been scarcely investigated. Recently, genetic studies have suggested that different metabolic pathways could be involved in the pathogenesis of migraine.Areas covered: This review focuses on cellular and molecular mechanisms involved in migraine, suggesting a role for circadian clocks, ion channels, synaptic plasticity, vascular factors, ion metal homeostasis, and impaired glucose metabolism in the pathogenesis of the disease. Accordingly, the article proposes new therapeutic targets that may be of particular relevance for disease prevention.Expert opinion: Several complex molecular mechanisms are involved in setting the genetic threshold for migraine and the pathogenesis of headache attacks. Most promising new therapeutic targets are the modulation of hypothalamic activity and ion channels involved in pain transmission. Further studies in animals and humans are necessary to enhance the elucidation of the molecular mechanisms of migraine and open new avenues for disease prevention.

Localising movement disorders in childhood

The diagnosis and management of movement disorders in children can be improved by understanding the pathways, neurons, ion channels, and receptors involved in motor learning and control. In this Review, we use a localisation approach to examine the anatomy, physiology, and circuitry of the basal ganglia and highlight the mechanisms that underlie some of the major movement disorders in children. We review the connections between the basal ganglia and the thalamus and cortex, address the basic clinical definitions of movement disorders, and then place diseases within an anatomical or physiological framework that highlights basal ganglia function. We discuss how new pharmacological, behavioural, and electrophysiological approaches might benefit children with movement disorders by modifying synaptic function. A better understanding of the mechanisms underlying movement disorders allows improved diagnostic and treatment decisions.

Identification of protein targets for the antidepressant effects of Kai-Xin-San in Chinese medicine using isobaric tags for relative and absolute quantitation

Kai-Xin-San consists of Ginseng Radix, Polygalae Radix, Acori Tatarinowii Rhizoma, and Poria at a ratio of 3:3:2:2. Kai-Xin-San has been widely used for the treatment of emotional disorders in China. However, no studies have identified the key proteins implicated in response to Kai-Xin-San treatment. In this study, rat models of chronic mild stress were established using different stress methods over 28 days. After 14 days of stress stimulation, rats received daily intragastric administrations of 600 mg/kg Kai-Xin-San. The sucrose preference test was used to determine depression-like behavior in rats, while isobaric tags were used for relative and absolute quantitation-based proteomics to identify altered proteins following Kai-Xin-San treatment. Kai-Xin-San treatment for 2 weeks noticeably improved depression-like behaviors in rats with chronic mild stress. We identified 33 differentially expressed proteins: 7 were upregulated and 26 were downregulated. Functional analysis showed that these differentially expressed proteins participate in synaptic plasticity, neurodevelopment, and neurogenesis. Our results indicate that Kai-Xin-San has an important role in regulating the key node proteins in the synaptic signaling network, and are helpful to better understand the mechanism of the antidepressive effects of Kai-Xin-San and to provide objective theoretical support for its clinical application. The study was approved by the Ethics Committee for Animal Research from the Chinese PLA General Hospital (approval No. X5-2016-07) on March 5, 2016.

Dystonia and dopamine: From phenomenology to pathophysiology

A line of evidence suggests that the pathophysiology of dystonia involves the striatum, whose activity is modulated among other neurotransmitters, by the dopaminergic system. However, the link between dystonia and dopamine appears complex and remains unclear. Here, we propose a physiological approach to investigate the clinical and experimental data supporting a role of the dopaminergic system in the pathophysiology of dystonic syndromes. Because dystonia is a disorder of motor routines, we first focus on the role of dopamine and striatum in procedural learning. Second, we consider the phenomenology of dystonia from every angle in order to search for features giving food for thought regarding the pathophysiology of the disorder. Then, for each dystonic phenotype, we review, when available, the experimental and imaging data supporting a connection with the dopaminergic system. Finally, we propose a putative model in which the different phenotypes could be explained by changes in the balance between the direct and indirect striato-pallidal pathways, a process critically controlled by the level of dopamine within the striatum. Search strategy and selection criteria References for this article were identified through searches in PubMed with the search terms « dystonia », « dopamine", « striatum », « basal ganglia », « imaging data », « animal model », « procedural learning », « pathophysiology », and « plasticity » from 1998 until 2018. Articles were also identified through searches of the authors' own files. Only selected papers published in English were reviewed. The final reference list was generated on the basis of originality and relevance to the broad scope of this review.

The spectrum of paroxysmal dyskinesias

Paroxysmal dyskinesias (PxD) comprise a group of heterogeneous syndromes characterized by recurrent attacks of mainly dystonia and/or chorea, without loss of consciousness. PxD have been classified according to their triggers and duration as paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia and paroxysmal exertion-induced dyskinesia. Of note, the spectrum of genetic and nongenetic conditions underlying PxD is continuously increasing, but not always a phenotype–etiology correlation exists. This creates a challenge in the diagnostic work-up, increased by the fact that most of these episodes are unwitnessed. Furthermore, other paroxysmal disorders, included those of psychogenic origin, should be considered in the differential diagnosis. In this review, some key points for the diagnosis are provided, as well as the appropriate treatment and future approaches discussed.

The genome of the live-bearing fish Heterandria formosa implicates a role of conserved vertebrate genes in the evolution of placental fish

Background

The evolution of complex organs is thought to occur via a stepwise process, each subsequent step increasing the organ’s complexity by a tiny amount. This evolutionary process can be studied by comparing closely related species that vary in the presence or absence of their organs. This is the case for the placenta in the live-bearing fish family Poeciliidae, as members of this family vary markedly in their ability to supply nutrients to their offspring via a placenta. Here, we investigate the genomic basis underlying this phenotypic variation in Heterandria formosa, a poeciliid fish with a highly complex placenta. We compare this genome to three published reference genomes of non-placental poeciliid fish to gain insight in which genes may have played a role in the evolution of the placenta in the Poeciliidae.

Results

We sequenced the genome of H. formosa, providing the first whole genome sequence for a placental poeciliid. We looked for signatures of adaptive evolution by comparing its gene sequences to those of three non-placental live-bearing relatives. Using comparative evolutionary analyses, we found 17 genes that were positively selected exclusively in H. formosa, as well as five gene duplications exclusive to H. formosa. Eight of the genes evolving under positive selection in H. formosa have a placental function in mammals, most notably endometrial tissue remodelling or endometrial cell proliferation.

Conclusions

Our results show that a substantial portion of positively selected genes have a function that correlates well with the morphological changes that form the placenta of H. formosa, compared to the corresponding tissue in non-placental poeciliids. These functions are mainly endometrial tissue remodelling and endometrial cell proliferation. Therefore, we hypothesize that natural selection acting on genes involved in these functions plays a key role in the evolution of the placenta in H. formosa.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1484-2) contains supplementary material, which is available to authorized users.

Postnatal developmental dynamics of cell type specification genes in Brn3a/Pou4f1 Retinal Ganglion Cells

BACKGROUND

About 20-30 distinct Retinal Ganglion Cell (RGC) types transmit visual information from the retina to the brain. The developmental mechanisms by which RGCs are specified are still largely unknown. Brn3a is a member of the Brn3/Pou4f transcription factor family, which contains key regulators of RGC postmitotic specification. In particular, Brn3a ablation results in the loss of RGCs with small, thick and dense dendritic arbors ('midget-like' RGCs), and morphological changes in other RGC subpopulations. To identify downstream molecular mechanisms underlying Brn3a effects on RGC numbers and morphology, our group recently performed a RNA deep sequencing screen for Brn3a transcriptional targets in mouse RGCs and identified 180 candidate transcripts.

METHODS

We now focus on a subset of 28 candidate genes encoding potential cell type determinant proteins. We validate and further define their retinal expression profile at five postnatal developmental time points between birth and adult stage, using in situ hybridization (ISH), RT-PCR and fluorescent immunodetection (IIF).

RESULTS

We find that a majority of candidate genes are enriched in the ganglion cell layer during early stages of postnatal development, but dynamically change their expression profile. We also document transcript-specific expression differences for two example candidates, using RT-PCR and ISH. Brn3a dependency could be confirmed by ISH and IIF only for a fraction of our candidates.

CONCLUSIONS

Amongst our candidate Brn3a target genes, a majority demonstrated ganglion cell layer specificity, however only around two thirds showed Brn3a dependency. Some were previously implicated in RGC type specification, while others have known physiological functions in RGCs. Only three genes were found to be consistently regulated by Brn3a throughout postnatal retina development - Mapk10, Tusc5 and Cdh4.

Postsynaptic RIM1 modulates synaptic function by facilitating membrane delivery of recycling NMDARs in hippocampal neurons

NMDA receptors (NMDARs) are crucial for excitatory synaptic transmission and synaptic plasticity. The number and subunit composition of synaptic NMDARs are tightly controlled by neuronal activity and sensory experience, but the molecular mechanism mediating NMDAR trafficking remains poorly understood. Here, we report that RIM1, with a well-established role in presynaptic vesicle release, also localizes postsynaptically in the mouse hippocampus. Postsynaptic RIM1 in hippocampal CA1 region is required for basal NMDAR-, but not AMPA receptor (AMPAR)-, mediated synaptic responses, and contributes to synaptic plasticity and hippocampus-dependent memory. Moreover, RIM1 levels in hippocampal neurons influence both the constitutive and regulated NMDAR trafficking, without affecting constitutive AMPAR trafficking. We further demonstrate that RIM1 binds to Rab11 via its N terminus, and knockdown of RIM1 impairs membrane insertion of Rab11-positive recycling endosomes containing NMDARs. Together, these results identify a RIM1-dependent mechanism critical for modulating synaptic function by facilitating membrane delivery of recycling NMDARs.

Rab3-interacting molecules (RIMs) are a key component of the presynaptic active zone that regulate neurotransmitter release. Here, the authors show that RIM1 also has postsynaptic function to organize NMDA receptors and synaptic response.

The PNKD gene is associated with Tourette Disorder or Tic disorder in a multiplex family

Tourette Disorder (TD) is a childhood-onset neuropsychiatric and neurodevelopmental disorder characterized by the presence of both motor and vocal tics. The genetic architecture of TD is believed to be complex and heterogeneous. Nevertheless, DNA sequence variants co-segregating with TD phenotypes within multiplex families have been identified. This report examines whole exomes of affected and unaffected individuals in a multiplex TD family to discover genes involved in the TD etiology. We performed whole exome sequencing on six out of nine members in a three-generation TD multiplex family. Putative deleterious sequence variants co-segregating with TD patients were identified by our in-house bioinformatics pipeline. Induced pluripotent stem cells (iPSCs) were generated from one unaffected and two TD affected individuals. Neurons were derived from the iPSCs and biochemical assays were conducted to evaluate possible molecular differences between affected and unaffected. A rare heterozygous nonsense mutation in PNKD was co-segregated with TD in this multiplex family. Transcript and protein levels of the PNKD long isoform were reduced in neurons derived from the individuals with TD due to the nonsense mutation, indicating nonsense-mediated mRNA decay. We demonstrated that the PNKD long isoform monomer oligomerizes with itself as well as interacts with the synaptic active zone protein RIMS1α. We concluded that reduced PNKD long isoform levels are detected in all affected individuals and we provide evidence for a mechanism whereby this might contribute to the TD phenotype.

A role for cerebellum in the hereditary dystonia DYT1

DYT1 is a debilitating movement disorder caused by loss-of-function mutations in torsinA. How these mutations cause dystonia remains unknown. Mouse models which have embryonically targeted torsinA have failed to recapitulate the dystonia seen in patients, possibly due to differential developmental compensation between rodents and humans. To address this issue, torsinA was acutely knocked down in select brain regions of adult mice using shRNAs. TorsinA knockdown in the cerebellum, but not in the basal ganglia, was sufficient to induce dystonia. In agreement with a potential developmental compensation for loss of torsinA in rodents, torsinA knockdown in the immature cerebellum failed to produce dystonia. Abnormal motor symptoms in knockdown animals were associated with irregular cerebellar output caused by changes in the intrinsic activity of both Purkinje cells and neurons of the deep cerebellar nuclei. These data identify the cerebellum as the main site of dysfunction in DYT1, and offer new therapeutic targets.

DOI:http://dx.doi.org/10.7554/eLife.22775.001

Dystonia is the third most common type of movement disorder after Parkinson’s disease and tremor. Patients with dystonia experience prolonged involuntary contractions of their muscles, often causing uncontrollable postures or repetitive movements. Almost thirty years ago, genetic studies revealed that a mutation in the gene that encodes a protein called torsinA causes the most common type of dystonia, called DYT1.

Exactly how mutations that affect the torsinA protein give rise to DYT1 remains unclear, and there are still no effective treatments for the disorder. Part of the problem is that we do not fully understand how torsinA works, or which of its many proposed functions is relevant to dystonia. Moreover, attempts to study DYT1 using genetically modified mice have proved largely unsuccessful. This is because mice that simply express the same genetic mutations that cause dystonia in humans do not show the overt symptoms of dystonia.

Fremont, Tewari et al. have now generated a mouse ‘model’ that does show symptoms of dystonia, and used these model mice to investigate the role of torsinA in the disorder. Acutely reducing the amount of torsinA protein in a region of the brain called the cerebellum induced the symptoms of dystonia in the mice. Conversely, reducing the amount of torsinA in a different brain area known as the basal ganglia had no such effect, even though both the cerebellum and the basal ganglia contribute to movement. Furthermore, neither manipulation had any effect in juvenile mice, which suggests that, in contrast to humans, young mice can compensate for the loss of torsinA.

Fremont, Tewari et al. also found that the loss of torsinA causes the cerebellum to generate incorrect output signals, which in turn trigger the abnormal movements seen in dystonia. In the future, further studies of the model mice could identify the exact changes that occur in neurons following the loss of torsinA from the cerebellum. Understanding these changes could potentially pave the way for developing effective treatments for DYT1 and other dystonias.

DOI:http://dx.doi.org/10.7554/eLife.22775.002

Synaptic UNC13A protein variant causes increased neurotransmission and dyskinetic movement disorder

Munc13 proteins are essential regulators of neurotransmitter release at nerve cell synapses. They mediate the priming step that renders synaptic vesicles fusion-competent, and their genetic elimination causes a complete block of synaptic transmission. Here we have described a patient displaying a disorder characterized by a dyskinetic movement disorder, developmental delay, and autism. Using whole-exome sequencing, we have shown that this condition is associated with a rare, de novo Pro814Leu variant in the major human Munc13 paralog UNC13A (also known as Munc13-1). Electrophysiological studies in murine neuronal cultures and functional analyses in Caenorhabditis elegans revealed that the UNC13A variant causes a distinct dominant gain of function that is characterized by increased fusion propensity of synaptic vesicles, which leads to increased initial synaptic vesicle release probability and abnormal short-term synaptic plasticity. Our study underscores the critical importance of fine-tuned presynaptic control in normal brain function. Further, it adds the neuronal Munc13 proteins and the synaptic vesicle priming process that they control to the known etiological mechanisms of psychiatric and neurological synaptopathies.

The epileptic and nonepileptic spectrum of paroxysmal dyskinesias: Channelopathies, synaptopathies, and transportopathies

Historically, the syndrome of primary paroxysmal dyskinesias was considered a group of disorders as a result of ion channel dysfunction. This proposition was primarily based on the discovery of mutations in ion channels, which caused other episodic neurological disorders such as epilepsy and migraine and also supported by the frequent association between paroxysmal dyskinesias and epilepsy. However, the discovery of the genes responsible for the 3 classic forms of paroxysmal dyskinesias disproved this ion channel theory. On the other hand, novel gene mutations implicating ion channels have been recently reported to produce episodic movement disorders clinically similar to the classic paroxysmal dyskinesias. Here, we review the clinical and pathophysiological aspects of the paroxysmal dyskinesias, further proposing a pathophysiological framework according to which they can be classified as synaptopathies (proline-rich transmembrane protein 2 and myofibrillogenesis regulator gene), channelopathies (calcium-activated potassium channel subunit alpha-1 and voltage-gated sodium channel type 8), or transportopathies (solute carrier family 2 member 1). This proposal might serve to explain similarities and differences among the various paroxysmal dyskinesias in terms of clinical features, treatment response, and natural history. © 2017 International Parkinson and Movement Disorder Society.

A homozygous PIGN missense mutation in Soft-Coated Wheaten Terriers with a canine paroxysmal dyskinesia

Hereditary paroxysmal dyskinesias (PxD) are a heterogeneous group of movement disorders classified by frequency, duration, and triggers of the episodes. A young-adult onset canine PxD has segregated as an autosomal recessive trait in Soft-Coated Wheaten Terriers. The medical records and videos of episodes from 25 affected dogs were reviewed. The episodes of hyperkinesia and dystonia lasted from several minutes to several hours and could occur as often as >10/day. They were not associated with strenuous exercise or fasting but were sometimes triggered by excitement. The canine PxD phenotype most closely resembled paroxysmal non-kinesigenic dyskinesia (PNKD) of humans. Whole genome sequences were generated with DNA from 2 affected dogs and analyzed in comparison to 100 control canid whole genome sequences. The two whole genome sequences from dogs with PxD had a rare homozygous PIGN:c.398C > T transition, which predicted the substitution of an isoleucine for a highly conserved threonine in the encoded enzyme. All 25 PxD-affected dogs were PIGN:c.398T allele homozygotes, whereas there were no c.398T homozygotes among 1185 genotyped dogs without known histories of PxD. PIGN encodes an enzyme involved in the biosynthesis of glycosylphosphatidylinositol (GPI), which anchors a variety of proteins including CD59 to the cell surface. Flow cytometry of PIGN-knockout HEK239 cells expressing recombinant human PIGN with the c.398T variant showed reduced CD59 expression. Mutations in human PIGN have been associated with multiple congenital anomalies-hypotonia-seizures syndrome-1 (MCAHS1). Movement disorders can be a part of MCAHS1, but this is the first PxD associated with altered GPI anchor function.

The PRRT2 knockout mouse recapitulates the neurological diseases associated with PRRT2 mutations

Heterozygous and rare homozygous mutations in PRoline-Rich Transmembrane protein 2 (PRRT2) underlie a group of paroxysmal disorders including epilepsy, kinesigenic dyskinesia episodic ataxia and migraine. Most of the mutations lead to impaired PRRT2 expression and/or function. Recently, an important role for PRTT2 in the neurotransmitter release machinery, brain development and synapse formation has been uncovered. In this work, we have characterized the phenotype of a mouse in which the PRRT2 gene has been constitutively inactivated (PRRT2 KO). β-galactosidase staining allowed to map the regional expression of PRRT2 that was more intense in the cerebellum, hindbrain and spinal cord, while it was localized to restricted areas in the forebrain. PRRT2 KO mice are normal at birth, but display paroxysmal movements at the onset of locomotion that persist in the adulthood. In addition, adult PRRT2 KO mice present abnormal motor behaviors characterized by wild running and jumping in response to audiogenic stimuli that are ineffective in wild type mice and an increased sensitivity to the convulsive effects of pentylentetrazol. Patch-clamp electrophysiology in hippocampal and cerebellar slices revealed specific effects in the cerebellum, where PRRT2 is highly expressed, consisting in a higher excitatory strength at parallel fiber-Purkinje cell synapses during high frequency stimulation. The results show that the PRRT2 KO mouse reproduces the motor paroxysms present in the human PRRT2-linked pathology and can be proposed as an experimental model for the study of the pathogenesis of the disease as well as for testing personalized therapeutic approaches.

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PRRT2 is intensely expressed in cerebellum and in restricted areas of the forebrain.

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PRRT2 KO mice display paroxysmal movements at the onset of locomotion.

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PRRT2 KO mice present abnormal motor behaviors in response to audiogenic stimuli.

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PRRT2 KO mice are more sensitive to the convulsive effects of pentylentetrazol.

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PRRT2 KO mice display an altered synaptic transmission in the cerebellar cortex.

Paroxysmal movement disorders: An update

Paroxysmal movement disorders comprise both paroxysmal dyskinesia, characterized by attacks of dystonic and/or choreic movements, and episodic ataxia, defined by attacks of cerebellar ataxia. They may be primary (familial or sporadic) or secondary to an underlying cause. They can be classified according to their phenomenology (kinesigenic, non-kinesigenic or exercise-induced) or their genetic cause. The main genes involved in primary paroxysmal movement disorders include PRRT2, PNKD, SLC2A1, ATP1A3, GCH1, PARK2, ADCY5, CACNA1A and KCNA1. Many cases remain genetically undiagnosed, thereby suggesting that additional culprit genes remain to be discovered. The present report is a general overview that aims to help clinicians diagnose and treat patients with paroxysmal movement disorders.

The clinical and genetic heterogeneity of paroxysmal dyskinesias

The contributions of different genes to inherited paroxysmal movement disorders are incompletely understood. Gardiner et al. identify mutations in 47% of 145 individuals with paroxysmal dyskinesias, with PRRT2 mutations in 35%, SLC2A1 in 10% and PNKD in 2%. New mutations expand the associated phenotypes and implicate overlapping mechanisms.

Paroxysmal dyskinesia can be subdivided into three clinical syndromes: paroxysmal kinesigenic dyskinesia or choreoathetosis, paroxysmal exercise-induced dyskinesia, and paroxysmal non-kinesigenic dyskinesia. Each subtype is associated with the known causative genes PRRT2, SLC2A1 and PNKD, respectively. Although separate screening studies have been carried out on each of the paroxysmal dyskinesia genes, to date there has been no large study across all genes in these disorders and little is known about the pathogenic mechanisms. We analysed all three genes (the whole coding regions of SLC2A1 and PRRT2 and exons one and two of PNKD) in a series of 145 families with paroxysmal dyskinesias as well as in a series of 53 patients with familial episodic ataxia and hemiplegic migraine to investigate the mutation frequency and type and the genetic and phenotypic spectrum. We examined the mRNA expression in brain regions to investigate how selective vulnerability could help explain the phenotypes and analysed the effect of mutations on patient-derived mRNA. Mutations in the PRRT2, SLC2A1 and PNKD genes were identified in 72 families in the entire study. In patients with paroxysmal movement disorders 68 families had mutations (47%) out of 145 patients. PRRT2 mutations were identified in 35% of patients, SLC2A1 mutations in 10%, PNKD in 2%. Two PRRT2 mutations were in familial hemiplegic migraine or episodic ataxia, one SLC2A1 family had episodic ataxia and one PNKD family had familial hemiplegic migraine alone. Several previously unreported mutations were identified. The phenotypes associated with PRRT2 mutations included a high frequency of migraine and hemiplegic migraine. SLC2A1 mutations were associated with variable phenotypes including paroxysmal kinesigenic dyskinesia, paroxysmal non-kinesigenic dyskinesia, episodic ataxia and myotonia and we identified a novel PNKD gene deletion in familial hemiplegic migraine. We found that some PRRT2 loss-of-function mutations cause nonsense mediated decay, except when in the last exon, whereas missense mutations do not affect mRNA. In the PNKD family with a novel deletion, mRNA was truncated losing the C-terminus of PNKD-L and still likely loss-of-function, leading to a reduction of the inhibition of exocytosis, and similar to PRRT2, an increase in vesicle release. This study highlights the frequency, novel mutations and clinical and molecular spectrum of PRRT2, SLC2A1 and PNKD mutations as well as the phenotype–genotype overlap among these paroxysmal movement disorders. The investigation of paroxysmal movement disorders should always include the analysis of all three genes, but around half of our paroxysmal series remain genetically undefined implying that additional genes are yet to be identified.

The contributions of different genes to inherited paroxysmal movement disorders are incompletely understood. Gardiner et al. identify mutations in 47% of 145 individuals with paroxysmal dyskinesias, with PRRT2 mutations in 35%, SLC2A1 in 10% and PNKD in 2%. New mutations expand the associated phenotypes and implicate overlapping mechanisms.