Genetics of paroxysmal dyskinesias

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.

Olfactory Neuroepithelium Cells from Cannabis Users Display Alterations to the Cytoskeleton and to Markers of Adhesion, Proliferation and Apoptosis

Cannabis is the third most commonly used psychoactive substance of abuse, yet it also receives considerable attention as a potential therapeutic drug. Therefore, it is essential to fully understand the actions of cannabis in the human brain. The olfactory neuroepithelium (ON) is a peripheral nervous tissue that represents an interesting surrogate model to study the effects of drugs in the brain, since it is closely related to the central nervous system, and sensory olfactory neurons are continually regenerated from populations of stem/progenitor cells that undergo neurogenesis throughout life. In this study, we used ON cells from chronic cannabis users and healthy control subjects to assess alterations in relevant cellular processes, and to identify changes in functional proteomic pathways due to cannabis consumption. The ON cells from cannabis users exhibited alterations in the expression of proteins that were related to the cytoskeleton, cell proliferation and cell death, as well as, changes in proteins implicated in cancer, gastrointestinal and neurodevelopmental pathologies. Subsequent studies showed cannabis provoked an increase in cell size and morphological alterations evident through β-Tubulin III staining, as well as, enhanced beta-actin expression and a decrease in the ability of ON cells to undergo cell attachment, suggesting abnormalities of the cytoskeleton and cell adhesion system. Furthermore, these cells proliferated more and underwent less cell death. Our results indicate that cannabis may alter key processes of the developing brain, some of which are similar to those reported in mental disorders like DiGeorge syndrome, schizophrenia and bipolar disorder.

Paroxysmal Nonkinesigenic Dyskinesias Responsive to Carbamazepine in Fahr Syndrome: A Case Report

OBJECTIVE

This study aimed to report the case of a patient with paroxysmal nonkinesigenic dyskinesias and Fahr syndrome who had a marked response to carbamazepine.

METHODS

We present the case of a 57-year-old female patient with episodes of paroxysmal choreoathetoid dyskinesias in the oromandibular region and distal region of upper and lower extremities, with fluctuating dystonic postures in the same distribution; duration was variable ranging from 30 minutes to 3 hours. Laboratory studies were consistent with primary hyperparathyroidism with bilateral brain calcifications.

RESULTS

Treatment with low doses of carbamazepine was successful.

A case of congenital myopathy masquerading as paroxysmal dyskinesia

Gastroesophageal reflux (GER) disease is a significant comorbidity of neuromuscular disorders. It may present as paroxysmal dyskinesia, an entity known as Sandifer syndrome. A 6-week-old neonate presented with very frequent paroxysms of generalized stiffening and opisthotonic posture since day 22 of life. These were initially diagnosed as seizures and he was started on multiple antiepileptics which did not show any response. After a normal video electroencephalogram (VEEG) was documented, possibility of dyskinesia was kept. However, when he did not respond to symptomatic therapy, Sandifer syndrome was thought of and GER scan was done, which revealed severe GER. After his symptoms got reduced to some extent, a detailed clinical examination revealed abnormal facies with flaccid quadriparesis. Muscle biopsy confirmed the diagnosis of a specific congenital myopathy. On antireflux measures, those episodic paroxysms reduced to some extent. Partial response to therapy in GER should prompt search for an underlying secondary etiology.

Episodic and electrical nervous system disorders caused by nonchannel genes

As noted in the separate introduction to this special topic section, episodic and electrical disorders can appear quite different clinically and yet share many overlapping features, including attack precipitants, therapeutic responses, natural history, and the types of genes that cause many of the genetic forms (i.e., ion channel genes). Thus, as we mapped and attempted to clone genes causing other episodic disorders, ion channels were always outstanding candidates when they mapped to the critical region of linkage in such a family. However, some of these disorders do not result from mutations in channels. This realization has opened up large and exciting new areas for the pathogenesis of these disorders. In some cases, the mutations occur in genes of unknown function or without understanding of molecular pathogenesis. Recently, emerging insights into a fascinating group of episodic movement disorders, the paroxysmal dyskinesias, and study of the causative genes and proteins are leading to the emerging concept of episodic electric disorders resulting from synaptic dysfunction. Much work remains to be done, but the field is evolving rapidly. As it does, we have come to realize that the molecular pathogenesis of electrical and episodic disorders is more complex than a scenario in which such disorders are simply due to mutations in the primary determinants of membrane excitability (channels).

Episodic movement disorders: from phenotype to genotype and back

Episodic dyskinetic movement disorders are a heterogeneous group of rare conditions. Paroxysmal dyskinesias constitute the core of this group and usually exhibit normal interepisodic neurologic findings. Contrariwise, episodic dyskinesias occur as a particular feature of complex chronic neurologic disorders. Conjunction of accurate phenotyping with up-to-date methods of molecular genetics recently provided remarkable new insights concerning the genetic causes of episodic dyskinesia. The identification of heterozygous mutations in the PRRT2 gene in paroxysmal kinesigenic dyskinesia as well as in benign familial infantile seizures linked episodic movement disorders with epilepsy. Alternating hemiplegia of childhood, the prototype of a chronic multisystem disease with episodic dyskinesia as a clinical hallmark, was recently found to be caused by heterozygous de novo mutations in the ATP1A3 gene. The clinical spectra of PRRT2 as well as of ATP1A3 mutations are still expanding. This review summarizes new genetic findings and clinical aspects in episodic dyskinesias.

Paroxysmale Dyskinesien

Paroxysmale Dyskinesien (PD) sind eine heterogene Gruppe von Erkrankungen, die durch plötzliche Attacken von unwillkürlichen Hyperkinesien gekennzeichnet sind. Selten sind sie symptomatisch bedingt (z. B. durch ursächliche Läsionen in den Basalganglien). Die überwiegende Zahl ist genetisch bedingt. Aufgrund der Triggerfaktoren werden sie klinisch in kinesiogene (PKC/PKD/DYT10), nonkinesiogene (PNKD/DYT8) und belastungsinduzierte Formen (PED/DYT18) eingeteilt. Die ersten Gene wurden für PNKD (MR1) und PED (SLC2A1) beschrieben. Während die Funktion des MR1-Proteins noch wenig verstanden ist, führen SLC2A1-Mutationen zu einem reduzierten Glukosetransport über die Blut-Hirn-Schranke. Kürzlich wurden bei Patienten mit PKD Mutationen in PRRT2 beschrieben, das für den neuronalen synaptischen vesikulären Zyklus wichtig zu sein scheint. Diese Übersicht fasst die klinischen Symptome, bildgebenden Befunde, Pathophysiologie und die therapeutischen Möglichkeiten für die verschiedenen PD zusammen.

Pathological laughter associated with paroxysmal kinesigenic dyskinesia: A rare presentation of acute disseminated encephalomyelitis

A 13-year-old boy presented with recurrent episodes of sudden brief posturing of the right upper and lower limbs accompanied by transient inability to speak and a tendency to smile which would sometimes break into laughter. Awareness was retained during the attack, and there was no associated emotional abnormality. The events were precipitated by walking and occurred several times in a day. The laughter was pathological in nature, and the abnormal posturing was akin to ‘paroxysmal kinesigenic dyskinesia’ (PKD). ‘Pathological laughter or crying’ is defined as an involuntary, inappropriate, unmotivated laughter, crying or both, without any associated mood change. It can occur as a result of cerebral lesions like tumors, trauma, vascular insults, multiple sclerosis and/or degenerative disorders. It can also be a component of gelastic epilepsy which is characterized by stereotyped recurrences, presence of interictal and ictal epileptiform discharges and absence of external precipitants. In our patient, however, there was no ictal or interictal EEG correlate. Paroxysmal kinesigenic dyskinesia is characterized by intermittent, involuntary movements triggered by kinesigenic stimuli and is usually familial but can also be secondary to metabolic and structural brain disorders. Magnetic Resonance Imaging (MRI), in our case, revealed multiple T2 and FLAIR hyperintense, non-enhancing lesions in the periaqueductal gray matter, pontine and midbrain tegmentum, bilateral thalami and left lentiform nucleus suggesting a diagnosis of ‘acute disseminated encephalomyelitis’, in which this unique combination of pathological laughter and PKD has not been described so far. Magnetic Resonance Spectroscopy (MRS) confirmed a demyelinating pathology, and the patient responded well to steroids.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.

A canine BCAN microdeletion associated with episodic falling syndrome

Episodic falling syndrome (EFS) is a canine paroxysmal hypertonicity disorder found in Cavalier King Charles spaniels. Episodes are triggered by exercise, stress or excitement and characterized by progressive hypertonicity throughout the thoracic and pelvic limbs, resulting in a characteristic 'deer-stalking' position and/or collapse. We used a genome-wide association strategy to map the EFS locus to a 3.48 Mb critical interval on canine chromosome 7. By prioritizing candidate genes on the basis of biological plausibility, we found that a 15.7 kb deletion in BCAN, encoding the brain-specific extracellular matrix proteoglycan brevican, is associated with EFS. This represents a compelling causal mutation for EFS, since brevican has an essential role in the formation of perineuronal nets governing synapse stability and nerve conduction velocity. Mapping of the deletion breakpoint enabled the development of Multiplex PCR and Multiplex Ligation-dependent Probe Amplification (MLPA) genotyping tests that can accurately distinguish normal, carrier and affected animals. Wider testing of a larger population of CKCS dogs without a history of EFS from the USA revealed that carriers are extremely common (12.9%). The development of molecular genetic tests for the EFS microdeletion will allow the implementation of directed breeding programs aimed at minimizing the number of animals with EFS and enable confirmatory diagnosis and pharmacotherapy of affected dogs.

Treatment of paroxysmal dyskinesias

IMPORTANCE OF THE FIELD

Paroxysmal dyskinesias represent a heterogeneous group of rare diseases sharing characteristics with two important groups of neurological disorders, the movement disorders and the epilepsies. Their common hallmark is the paroxysmal occurrence of dyskinesias including athetosis, ballism, chorea and dystonia. During the last two decades, various genetic abnormalities have been identified thereby providing insight into the underlying pathophysiology and offering therapeutic opportunities for many of these conditions.

AREAS COVERED IN THIS REVIEW

We summarize the diagnostic criteria of idiopathic and symptomatic paroxysmal dyskinesias and describe their therapeutic options. For the preparation of this review article, an extensive literature search was undertaken using PubMed.

WHAT THE READER WILL GAIN

This review provides a practical guide to the diagnosis and treatment of paroxysmal dyskinesias.

TAKE HOME MESSAGE

The mainstay of therapy is carbamazepine for paroxysmal kinesigenic dyskinesias and clonazepam for the nonkinesigenic dyskinesias. In symptomatic paroxysmal dyskinesias, the treatment of the underlying disease will provide best results. The ketogenic diet for patients with paroxysmal exertion-induced dyskinesias is a promising new therapeutic strategy and may not only prevent attacks but also lead to improvement of developmental delay in affected children.

Bilateral striopallidodentate calcinosis with paroxysmal kinesigenic dyskinesia

Bilateral striopallidodentate calcinosis is characterized by calcification of the basal ganglia and other gray matter structures. We describe a 16-year-old boy with paroxysmal kinesigenic dyskinesia. He exhibited mineralization in the basal ganglia, posterior thalami, and dentate nuclei bilaterally, and was diagnosed with sporadic bilateral striopallidodentate calcinosis. The paroxysmal kinesigenic dyskinesia responded to low-dose treatment with carbamazepine (200 mg/day).