Genetic and clinical heterogeneity in paroxysmal kinesigenic dyskinesia: evidence for a third EKD gene

PRRT2 Related Epilepsies: A Gene Review

PRRT2 encodes for proline-rich transmembrane protein 2 involved in synaptic vesicle fusion and presynaptic neurotransmitter release. Mutations in human PRRT2 have been related to paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions with choreoathetosis, benign familial infantile epilepsies, and hemiplegic migraine. PRRT2 mutations cause neuronal hyperexcitability, which could be related to basal ganglia or cortical circuits dysfunction, leading to paroxysmal disorders. PRRT2 is expressed in the cerebral cortex, basal ganglia, and cerebellum. Approximately, 90% of pathogenic variants are inherited and 10% are de novo. Paroxysmal attacks in PKD are characterized by dystonia, choreoathetosis, and ballismus. In the benign familial infantile epilepsy (BFIE), seizures are usually focal with or without generalization, usually begin between 3 and 12 months of age and remit by 2 years of age. In 30% of cases of PRRT2-associated PKD, there is an association with BFIE, and this entity is referred to as PKD with infantile convulsions (PKD/IC). PRRT2 mutations are the cause of benign family childhood epilepsy and PKD/IC. On the other hand, PRRT2 mutations do not seem to correlate with other types of epilepsy. The increasing incidence of hemiplegic migraine in families with PRRT2-associated PKD or PKD/IC suggests a common disease pathway, and it is possible to assert that BFIE, paroxysmal kinesigenic dyskinesia, and PKD with IC belong to a continuous disease spectrum of PRRT2-associated diseases.

Exercise test for patients with new-onset paroxysmal kinesigenic dyskinesia

The pathogenesis of primary paroxysmal kinesigenic dyskinesia (PKD) remains unclear, and channelopathy is a possibility. In a pilot study, we found that PKD patients had abnormal exercise test (ET) results. To investigate the ET performances in patients affected by PKD, and the role of the channelopathies in the pathogenesis of PKD, we compared the ET results of PKD patients, control subjects, and hypokalemic periodic paralysis (HoPP) patients, and we analyzed ET changes in 32 PKD patients before and after treatment. Forty-four PKD patients underwent genetic testing for the PRRT2, SCN4A, and CLCN1 genes. Sixteen of 59 (27%) patients had abnormal ET results in the PKD group, while 28 of 35 (80%) patients had abnormal ET results in the HoPP group. Compared with the control group, the PKD group showed a significant decrease in the compound muscle action potential (CMAP) amplitude and area after the long ET (LET), while the HoPP group showed not only greater decreases in the CMAP amplitude and area after the LET but also greater increases in the CMAP amplitude and area immediately after the LET. The ET parameters before and after treatment were not significantly different. Nine of 44 PKD patients carried PRRT2 mutations, but the gene abnormalities were unrelated to any ET parameter. The PKD group demonstrated an abnormal LET result by electromyography (EMG), and this abnormality did not seem to correlate with the PRRT2 variant or sodium channel blocker therapy.

Paroxysmal dyskinesia and epilepsy in pseudohypoparathyroidism

Background

Paroxysmal kinesigenic dyskinesia (PKD) and epilepsy share common pathogenic mechanisms but their pathophysiological connections remain unknown. Our study reports an individual with both disorders as a consequence of pseudohypoparathyroidism (PHP). This observation suggests potential shared pathophysiological mechanisms between PKD and epilepsy.

Methods

We report the case of a 15‐year‐old male with pre‐diagnosed PKD and symptomatic epilepsy. We recorded the symptoms and carried out comprehensive biochemical, genetic, imaging, and EEG analyses to examine the characteristics and potentially shared etiology of these conditions.

Results

In this case, the patient's PKD and symptomatic epilepsy were secondary to pseudohypoparathyroidism (PHP). The patient had a seven‐year history of intermittent, involuntary paroxysmal episodic movements, and a six‐year history of a loss of consciousness with convulsions. The electroencephalography results showed that the paroxysmal low and medium amplitude slow waves, isolated sharp waves, and sharp slow‐wave release occurred in the right prefrontal temporal cortex. Serum analysis indicated a calcium concentration of 1.91 mmol/L, a phosphorus concentration of 2.68 mmol/L, an alkaline phosphatase concentration of 114 IU/L, and a parathyroid hormone concentration of 109 pg/ml. Computerized tomography and magnetic resonance imaging results showed multiple calcifications in the bilateral frontal and parietal lobe cortex, bilateral thalamus, basal ganglia, and centrum semiovale. Furthermore, GNAS methylation abnormalities were discovered during methylation testing. There was no recurrence of abnormal movements or epileptic seizures, and calcium concentrations returned to healthy levels, following the pharmacological treatment of PHP.

Conclusion

In this case, PKD and symptomatic epilepsy were caused by PHP. This report underscores the importance of looking for biochemical abnormalities in PKD and symptomatic epilepsy patients. We suggest that all such intractable epilepsy seizure patients should be screened for PHP.

Paroxysmal Kinesigenic Dyskinesia: First Molecularly Confirmed Case from Africa

Background

Paroxysmal kinesigenic dyskinesia (PKD) is a movement disorder, with an excellent response to carbamazepine treatment. It has been described in various populations, but not yet in an African population.

Case report

In a patient who reported to clinic with side effects of carbamazepine, PRRT2 gene screening was performed based on a clinical history compatible with PKD. A common PRRT2 mutation was identified in this patient, hereby the first genetically confirmed PRRT2-associated PKD in Africa.

Discussion

Reporting genetic confirmation of an unusual movement disorder from an equally unusual location shows the wide geographical distribution of PRRT2-associated disease. It also illustrates recognizability of this treatable disorder where the easiest accessible diagnostic tool is neurological history and examination.

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.

Novel Locus for Paroxysmal Kinesigenic Dyskinesia Mapped to Chromosome 3q28-29

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by recurrent and brief attacks of dystonia or chorea precipitated by sudden movements. It can be sporadic or familial. Proline-Rich Transmembrane Protein 2 (PRRT2) has been shown to be a common causative gene of PKD. However, less than 50% of patients with primary PKD harbor mutations in PRRT2. The aim of this study is to use eight families with PKD to identify the pathogenic PRRT2 mutations, or possible novel genetic cause of PKD phenotypes. After extensive clinical investigation, direct sequencing and mutation analysis of PRRT2 were performed on patients from eight PKD families. A genome-wide STR and SNP based linkage analysis was performed in one large family that is negative for pathogenic PRRT2 mutations. Using additional polymorphic markers, we identified a novel gene locus on chromosome 3q in this PRRT2-mutation-negative PKD family. The LOD score for the region between markers D3S1314 and D3S1256 is 3.02 and we proposed to designate this locus as Episodic Kinesigenic Dyskinesia (EKD3). Further studies are needed to identify the causative gene within this locus.

Paroxysmal movement disorders

Paroxysmal dyskinesias represent a group of episodic abnormal involuntary movements manifested by recurrent attacks of dystonia, chorea, athetosis, or a combination of these disorders. Paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, paroxysmal exertion-induced dyskinesia, and paroxysmal hypnogenic dyskinesia are distinguished clinically by precipitating factors, duration and frequency of attacks, and response to medication. Primary paroxysmal dyskinesias are usually autosomal dominant genetic conditions. Secondary paroxysmal dyskinesias can be the symptoms of different neurologic and medical disorders. This review summarizes the updates on etiology, pathophysiology, genetics, clinical presentation, differential diagnosis, and treatment of paroxysmal dyskinesias and other episodic movement disorders.

Five cases of paroxysmal kinesigenic dyskinesia by genetic diagnosis

Paroxysmal kinesigenic dyskinesia (PKD) is an autosomal dominant disorder and PRRT2 is the causative gene of PKD. The aim of this study was to investigate PRRT2 mutations in patients who were clinically diagnosed with PKD. Nine PKD cases, including four familial cases and five sporadic cases, were selected. Peripheral blood was drawn after obtaining informed consent, and genomic DNA was extracted by a standard protocol. Sanger sequencing was performed for the screening of PRRT2 mutations. A total of five cases were detected to harbor PRRT2 mutations. Four familial cases carried a c.649dupC (p.Arg217Profs^*8) mutation, while one sporadic case and his asymptomatic father carried a c.133-136delCCAG (p.Pro45Argfs^*44) mutation. PRRT2 mutations were not identified in the remaining cases. The study further confirmed that PRRT2 was a causative gene of PKD and implied that PRRT2 mutation has incomplete penetrance.

Molecular analysis of PRRT2 gene in a case of paroxysmal kinesigenic dyskinesia patient

Paroxysmal kinesigenic dyskinesia (PKD) is an abnormal involuntary movement that is episodic or intermittent, with sudden onset, and the attacks are induced by sudden movement. Mutations in proline-rich transmembrane protein 2 (PRRT2) gene have been implicated in the cause of this disorder. This study presents a case of PKD on the basis of clinical findings supported and evidences obtained through a mutational analysis. Sequencing of all the exons of PRRT2 gene revealed a frameshift mutation (p.R217Pfs*8) in exon 2 and a novel transition mutation (c.244C > T) in 5′-untranslated region (UTR). Though mutations in PRRT2 gene are well-established in PKD, this study for the first time presents a novel transition mutation in the exon 2 region.

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.

Primary dystonias and genetic disorders with dystonia as clinical feature of the disease

Dystonia is probably the most common form of movement disorder encountered in the clinical practice. It is characterized by sustained muscle contractions, usually producing twisting and repetitive movements or abnormal postures or positions. Dystonias can be classified in several ways, including primarily by the clinical phenomenology or by the underlining etiology, in particular to understand if the presentation is genetically determined. By advances of genetics, including contemporary genomic technologies, there is a growing understanding of the molecular underpinnings of genetically determined dystonias. The intricacy of information requires a user friendly, novel database that may efficiently serve clinicians to inform of advances of the field and to diagnose and manage these often complex cases. Here we present an up to date, comprehensive review - in tabulated formats - of genetically determined primary dystonias and complex Mendelian disorders with dystonia as central feature. The detailed search up to December 24, 2012, identified 24 hereditary primary dystonias (DYT1 to DYT 25) that are mostly monogenic disorders, and a larger group (>70) of genetic syndromes in which dystonia is one of the characteristic clinical features. We organized the findings not only by individual information (name of the conditions, pattern of inheritance, chromosome and gene abnormality, clinical features, relevant ancillary tests and key references), but also provide symptom-oriented organization of the clinical entities for efficient inquiries.

Hereditäre Dystonien

Dystonien sind eine klinisch und ätiologisch heterogene Gruppe von Bewegungsstörungen. Charakteristisch sind unwillkürliche Muskelkontraktionen, die zu drehenden, schraubenden und repetitiven Bewegungen führen und sehr schmerzhaft sein können. Die Dystonie kann dabei das einzige Symptom sein („isolierte Dystonie“) oder von anderen Symptomen begleitet werden („kombinierte Dystonie“), sie kann aber auch eine Manifestation jedweder das Zentralnervensystem betreffenden Erkrankung sein, die das motorische System in Mitleidenschaft zieht (z. B. neurodegenerative, ischämische, traumatische Prozesse). In den letzten 20 Jahren hat die Entwicklung neuer molekulargenetischer Technologien zur Entdeckung neuer Gene geführt, die vielen Dystoniesubtypen zugrunde liegen, und eine verbesserte Klassifizierung sowie einen tieferen Einblick in die Pathophysiologie ermöglicht. Es wird eine aktuelle Übersicht über die genetisch determinierten Dystonien mit Fokus auf den sog. isolierten bzw. kombinierten Formen vorgelegt. Die Zusammenstellung phänotypischer Charakteristika zu spezifischen genetischen Veränderungen soll dem Kliniker ermöglichen, anhand konkreter klinischer Manifestationen eine entsprechende molekulargenetische Abklärung in die Wege zu leiten.

Clinical features of childhood-onset paroxysmal kinesigenic dyskinesia with PRRT2 gene mutations

AIM

To define better the phenotype and genotype of familial and sporadic cases of paroxysmal kinesigenic dyskinesia (PKD) caused by mutations in the PRRT2 gene presenting in the paediatric age group.

METHOD

We report the detailed clinical and molecular genetic features of 11 patients (six females, five males) with childhood-onset PRRT2-mutation-positive PKD.

RESULTS

Mean age at disease onset was 8 years 7.5 months (range 5-11y), and clinical presentation was characterized by daily short paroxysmal episodes of dystonia/dyskinesia. Most patients also had non-kinesigenic attacks in addition to the classical movement-induced paroxysmal episodes. One family demonstrated great phenotypic variability with PKD, infantile convulsions, and/or hemiplegic migraine affecting different family members with the same mutation. All patients in whom antiepileptics (carbamazepine/phenytoin) were tried showed a dramatic improvement with complete abolition of dyskinetic episodes.

INTERPRETATION

Our case series provides a detailed clinical description of patients with PRRT2-PKD, and reports a spectrum of disease-causing mutations, thereby expanding both the clinical phenotype and mutation spectrum of disease.

Clinical analysis of nine cases of paroxysmal exercise-induced dystonia

This study was aimed to analyze the clinical features of paroxysmal kinesigenic dyskinesia (PKD) and extend the understanding of this disease. From August, 2008 to October, 2010, 9 patients were diagnosed with PKD in the Department of Neurology of the First Affiliated Hospital of Zhejiang University, China. The data involving clinical demographic characteristics, somatosensory evoked potentials, results of electromyography, video electroencephalography (EEG), brain magnetic resonance imaging (MRI) and computerized tomography (CT) were collected. All PKD patients exhibited unilateral or bilateral recurrent episodic dyskinetic attacks triggered by sudden voluntary movements. The duration of the attacks ranged from several seconds to one minute. The attack frequency ranged from approximately once in several months to more than 10 times in a day. Patients suffered from no conscious disorders during the attack, and no neurological signs were found during the period between attacks. No abnormal somatosensory evoked potentials were found. Routine EEG, video EEG monitoring or brain imaging showed normal findings. Classical treatment for anti-epilepsy, including carbamazepine and topiramate, was administered to the patients and proved to be effective. It was concluded that PKD is characteristically triggered by sudden voluntary movement; no abnormal electroneurophysiological findings are observed in PKD, and antiepileptic drugs are effective in treating the disorder.

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.

Clinical features of paroxysmal kinesigenic dyskinesia: report of 24 cases

Paroxysmal kinesigenic dyskinesia (PKD) is the most common type of paroxysmal dyskinesia and is characterized by involuntary, intermittent movements induced by sudden movements. Here, we describe 24 patients with PKD, whose clinical data were analyzed. The attacks of involuntary movements were all short lasting, and could involve extremities, trunk, neck, or face without alteration of consciousness. The motor function was normal between attacks, and in some cases, attacks could be evoked during examination. Most patients had normal electroencephalogram (EEG) and neuroimaging results, but 2 cases had abnormal EEGs, and another 2 cases had bilateral calcification of basal ganglion on brain computed tomography (CT) scans. Previous history of misdiagnosis was a predominant feature, while treatments based on misdiagnosis sometimes did lead to improvement. Here, we discuss the clinical characteristics, especially the abnormalities of investigations and misdiagnosis, and recent insights into the pathophysiology of PKD.

PRRT2 gene mutations: from paroxysmal dyskinesia to episodic ataxia and hemiplegic migraine

OBJECTIVE

The proline-rich transmembrane protein (PRRT2) gene was recently identified using exome sequencing as the cause of autosomal dominant paroxysmal kinesigenic dyskinesia (PKD) with or without infantile convulsions (IC) (PKD/IC syndrome). Episodic neurologic disorders, such as epilepsy, migraine, and paroxysmal movement disorders, often coexist and are thought to have a shared channel-related etiology. To investigate further the frequency, spectrum, and phenotype of PRRT2 mutations, we analyzed this gene in 3 large series of episodic neurologic disorders with PKD/IC, episodic ataxia (EA), and hemiplegic migraine (HM).

METHODS

The PRRT2 gene was sequenced in 58 family probands/sporadic individuals with PKD/IC, 182 with EA, 128 with HM, and 475 UK and 96 Asian controls.

RESULTS

PRRT2 genetic mutations were identified in 28 out of 58 individuals with PKD/IC (48%), 1/182 individuals with EA, and 1/128 individuals with HM. A number of loss-of-function and coding missense mutations were identified; the most common mutation found was the p.R217Pfs*8 insertion. Males were more frequently affected than females (ratio 52:32). There was a high proportion of PRRT2 mutations found in families and sporadic cases with PKD associated with migraine or HM (10 out of 28). One family had EA with HM and another large family had typical HM alone.

CONCLUSIONS

This work expands the phenotype of mutations in the PRRT2 gene to include the frequent occurrence of migraine and HM with PKD/IC, and the association of mutations with EA and HM and with familial HM alone. We have also extended the PRRT2 mutation type and frequency in PKD and other episodic neurologic disorders.

Novel PRRT2 mutation in an African-American family with paroxysmal kinesigenic dyskinesia

Background

Recently, heterozygous mutations in PRRT2 (Chr 16p11.2) have been identified in Han Chinese, Japanese and Caucasians with paroxysmal kinesigenic dyskinesia. In previous work, a paroxysmal kinesigenic dyskinesia locus was mapped to Chr 16p11.2 - q11.2 in a multiplex African-American family.

Methods

Sanger sequencing was used to analyze all four PRRT2 exons for sequence variants in 13 probands (9 Caucasian, 1 Caucasian-Thai, 1 Vietnamese and 2 African-American) with some form of paroxysmal dyskinesia.

Results

One patient of mixed Caucasian-Thai background and one African-American family harbored the previously described hotspot mutation in PRRT2 (c.649dupC, p.R217Pfs*8). Another African-American family was found to have a novel mutation (c.776dupG, p.E260*). Both of these variants are likely to cause loss-of-function via nonsense-mediated decay of mutant PRRT2 transcripts. All affected individuals had classic paroxysmal kinesigenic dyskinesia phenotypes.

Conclusions

Heterozygous PRRT2 gene mutations also cause paroxysmal kinesigenic dyskinesia in African-Americans. The c.649dupC hotspot mutation in PRRT2 is common across racial groups.

Identification of PRRT2 as the causative gene of paroxysmal kinesigenic dyskinesias

Paroxysmal kinesigenic dyskinesias is a paroxysmal movement disorder characterized by recurrent, brief attacks of abnormal involuntary movements induced by sudden voluntary movements. Although several loci, including the pericentromeric region of chromosome 16, have been linked to paroxysmal kinesigenic dyskinesias, the causative gene has not yet been identified. Here, we identified proline-rich transmembrane protein 2 (PRRT2) as a causative gene of paroxysmal kinesigenic dyskinesias by using a combination of exome sequencing and linkage analysis. Genetic linkage mapping with 11 markers that encompassed the pericentromeric of chromosome 16 was performed in 27 members of two families with autosomal dominant paroxysmal kinesigenic dyskinesias. Then, the whole-exome sequencing was performed in three patients from these two families. By combining the defined linkage region (16p12.1–q12.1) and the results of exome sequencing, we identified an insertion mutation c.649_650InsC (p.P217fsX7) in one family and a nonsense mutation c.487C>T (p.Q163X) in another family. To confirm our findings, we sequenced the exons and flanking introns of PRRT2 in another three families with paroxysmal kinesigenic dyskinesias. The c.649_650InsC (p.P217fsX7) mutation was identified in two of these families, whereas a missense mutation, c.796C>T (R266W), was identified in another family with paroxysmal kinesigenic dyskinesias. All of these mutations completely co-segregated with the phenotype in each family. None of these mutations was identified in 500 normal unaffected individuals of matched geographical ancestry. Thus, we have identified PRRT2 as the first causative gene of paroxysmal kinesigenic dyskinesias, warranting further investigations to understand the pathogenesis of this disorder.

Diagnosis and treatment of paroxysmal dyskinesias revisited

Paroxysmal dyskinesias (PDs) are a rare group of hyperkinetic movement disorders mainly characterized by their episodic nature. Neurological examination may be entirely normal between the attacks. Three main types of PDs can be distinguished based on their precipitating events - (i) paroxysmal kinesigenic dyskinesias (PKD), (ii) paroxysmal non-kinesigenic dyskinesias (PNKD) and (iii) paroxysmal exercise-induced (exertion-induced) dyskinesias (PED). The diagnosis of PDs is based on their clinical presentation and precipitating events. Substantial progress has been made in the field of genetics and PDs. Treatment options mainly include anticonvulsants and benefit of treatment is depending on the type of PD. Most important differential diagnosis are non-epileptic psychogenic, non-epileptic organic and epileptic attack disorders, especially nocturnal frontal lobe epilepsy.

Paroxysmal dyskinesias

Paroxysmal movement disorders are a relatively rare and heterogenous group of conditions manifesting as episodic dyskinesia lasting a brief duration. Three forms are clearly recognized, namely, paroxysmal kinesigenic (PKD), nonkinisegenic (PNKD), and exercise induced (PED). There have been major advances in the understanding of the pathophysiological mechanisms and the genetics of these disorders, leading to better clinical definitions based on genotype-phenotype correlations in the familial idiopathic forms. PKD is genetically heterogenous, but there is linkage to chromosome 16 in a number of families. PNKD is due to mutations of the MR-1 gene. PED is genetically heterogenous, but a number of familial and sporadic cases may be due to GLUT-1 gene mutations. The GLUT1 gene-related form of PED may respond to a ketogenic diet. Potassium and calcium channel mutations underlie the 2 main forms of episodic ataxia (EA1 and EA2), whereas benign torticollis of infancy may also be a calcium channel disorder.

Milestones in dystonia

The last 25 years have seen remarkable advances in our understanding of the genetic etiologies of dystonia, new approaches into dissecting underlying pathophysiology, and independent progress in identifying effective treatments. In this review we highlight some of these advances, especially the genetic findings that have taken us from phenomenological to molecular-based diagnoses. Twenty DYT loci have been designated and 10 genes identified, all based on linkage analyses in families. Hand in hand with these genetic findings, neurophysiological and imaging techniques have been employed that have helped illuminate the similarities and differences among the various etiological dystonia subtypes. This knowledge is just beginning to yield new approaches to treatment including those based on DYT1 animal models. Despite the lag in identifying genetically based therapies, effective treatments, including impressive benefits from deep brain stimulation and botulinum toxin chemodenervation, have marked the last 25 years. The challenge ahead includes continued advancement into understanding dystonia's many underlying causes and associated pathology and using this knowledge to advance treatment including preventing genetic disease expression.

Paroxysmal dyskinesias

Paroxysmal dyskinesias are a rare group of movement disorders affecting both adults and children. Based on the events that precipitate the abnormal movements, they are subdivided into paroxysmal kinesigenic dyskinesia (PKD), precipitated by sudden voluntary movements; paroxysmal nonkinesigenic dyskinesia (PNKD), which occurs at rest; paroxysmal exertion-induced dyskinesia (PED), occurring after prolonged exercise; and paroxysmal hypnogenic dyskinesia (PHD), which occurs in sleep. Paroxysmal dyskinesias can be sporadic, familial (autosomal dominant inheritance), or secondary to other disorders. Recent genetic discoveries may aid us in elucidating the pathophysiology of these disorders. PKD has been linked to the pericentromeric region of chromosome 16, PNKD is associated with mutations in the myofibrillogenesis regulator 1 (MR-1) gene on the long arm of chromosome 2 (2q32-36 locus), and PED is associated with mutations in the glucose transporter gene, GLUT1, responsible for glucose transport across the blood-brain barrier. Lifestyle modification to avoid precipitating factors is important in the management of paroxysmal dyskinesias. Medical therapies have not been examined in controlled trials. Nevertheless, anticonvulsants have been found to be extremely effective in treating PKD and are sometimes useful in other types, suggesting that these disorders may indeed represent forms of channelopathies. Drugs such as acetazolamide, anticholinergics, levodopa, and tetrabenazine have been inconsistently successful. In rare cases with medically refractory symptoms, deep brain stimulation has also been employed. Development of successful treatments for the different paroxysmal dyskinesias rests on elucidating the pathophysiology and targeting therapy to treat the underlying perturbation.

Paroxysmal choreodystonic disorders

Paroxysmal choreodystonic disorders or paroxysmal dyskinesias are a heterogeneous group of movement disorders characterized by recurrent attacks of abnormal involuntary movements. They are classified into four categories according to the precipitant, duration of attacks, and etiology: (1) paroxysmal kinesigenic dyskinesia (PKD), in which attacks are brief and induced by sudden voluntary movements; (2) paroxysmal nonkinesigenic dyskinesia (PNKD), in which attacks occur spontaneously; (3) paroxysmal exertion-induced dyskinesia (PED), in which attacks are brought on by prolonged exercise; and (4) paroxysmal hypnogenic dyskinesia (PHD), in which attacks occur during sleep. Among them, PHD is currently known to be a form of mesial frontal-lobe epilepsy, and has been given the term "autosomal-dominant nocturnal frontal lobe epilepsy" (ANDFLE) in some familiar cases with an autosomal-dominant inheritance. The clinical, etiological and pathophysiological features of PKD, PNKD, and PED are reviewed.

Paroxysmal kinesigenic choreoathetosis: evidence of linkage to the pericentromeric region of chromosome 16 in four Chinese families

BACKGROUND

Paroxysmal kinesigenic choreoathetosis (PKC) is an autosomal dominant condition characterized by abnormal involuntary movements precipitated by sudden movement. The pericentromeric region of chromosome 16 has been linked to PKC by several reports. This study was to localize and identify PKC gene in four Chinese PKC families.

METHODS

Genetic linkage mapping with eight markers spanning chromosome 16p12-q13 was performed in 43 family members. Genome-wide single nucleotide polymorphism (SNP) scans were performed on four individuals in Family 1 in which infantile convulsion (IC) was co-inherited with PKC.

RESULTS

Individuals in Family 1 presented with both IC and paroxysmal choreoathetosis (ICCA), and Families 2, 3, and 4 presented only with PKC. Evidence for linkage was found with a maximum two-point LOD score of 4.89 for D16S690 (theta = 0.0) and a maximum multipoint LOD score was 5.34 between D16S3080 and D16S3136. Haplotype analysis showed the disease locus was between D16S3093 and D16S3057. A total of 84 SNPs spanned on 16q12.1-q13 was not segregated with the PKC phenotype, which defined an unlinked region from rs9933187 to rs8044753. Thus, the critical region of the PKC gene is across the pericentromeric region of chromosome 16, and most likely maps to a region of 20.5 Mb (6.2 cM) between D16S3093 and rs9933187 (16p11.2-q12.1).

CONCLUSION

The assignment of the locus for PKC to the pericentromeric region of chromosome 16 is confirmed and putatively narrowed in the present study.

[Paroxysmal kinesigenic dyskinesia: a channelopathy? Study of 19 cases]

INTRODUCTION

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by brief episodes of dystonia and choreoathetosis triggered by sudden voluntary movements. Disease onset is seen in the first or second decade. The attacks typically last less than one minute. Three autosomal dominant PKD loci are identified: EKD1, EKD2 and EKD3. EKD1 has an overlap with the locus of the "Infantile Convulsion and Choreoathetosis (ICCA) syndrome". The favorable natural history, the episodic nature of the symptoms and their sensitivity to anticonvulsant therapy suggest channelopathy as a mechanism of PKD.

PATIENTS AND METHODS

We reviewed the clinical features, the family history, the treatment response, the evolution and the technical investigations in 19 affected individuals.

RESULTS

All cases were idiopathic. Ten patients had a positive familial history. Three patients suffered from ICCA syndrome. Some atypical features were seen, such as the association of kinesigenic and nonkinesigenic attacks and the presence of migraine, ataxia, seizures and myoclonus. Acetazolamide responsiveness was seen in two patients.

CONCLUSION

The coexistence of PKD and nonkinesigenic dyskinesia in several patients confirms the earlier described presence of intermediary forms, nonrepresented in the current classification of paroxysmal dyskinesias. Our study results suggest channel dysfunction and basal ganglia involvement in the pathophysiology of PKD.

Paroxysmal dyskinesias

PURPOSE OF REVIEW

Substantial progress has been made recently in understanding characteristic features of the paroxysmal dyskinesias and underlying genetic causes. This review summarizes the most important findings and discusses their implications.

RECENT FINDINGS

The classification of paroxysmal dyskinesias has been confusing until recently when descriptive schemes were advocated over historical terminology. The descriptive classification scheme has aided phenotypic characterization in genetic studies. Recent genetic studies have revealed causes for some of the more important forms of paroxysmal dyskinesias. In particular, the major form of paroxysmal nonkinesigenic dyskinesia has been shown not to be a channelopathy. Furthermore, substantial phenotypic homogeneity has been demonstrated with each type of paroxysmal dyskinesia.

SUMMARY

The recent phenotype characterization and genetic studies have provided important information that simplified the diagnosis and treatment of the paroxysmal dyskinesias. These advances enhance our understanding of mechanisms underlying paroxysmal nonepileptic as well as some epileptic disorders.

Localization and mutation detection for paroxysmal kinesigenic choreoathetosis

BACKGROUND

Paroxysmal kinesigenic choreoathetosis (PKC) is an autosomal-dominant movement disorder characterized by attacks of paroxysmal involuntary movements. To date, the causative gene has not been discovered.

PURPOSE

The purpose of the study is to localize the causative region and detect the causative mutation.

METHODS

A PKC family including 16 subjects (5 cases and 11 controls) in Zhejiang Province was recruited. Nine microsatellite markers on chromosome 16 were selected and genotyped. Two-point LOD scores were calculated. After preliminary localization, CACNG3, IL4R and ABCC11 were selected as candidate genes and were detected by polymerase chain reaction-sequencing or PCR-denaturing high performance liquid chromatography (PCR-DHPLC).

RESULTS

The maximal two-point LOD score was obtained in D16S3081 with 1.21, and haplotype analysis revealed almost all of individuals carrying 5-3-8-3-4-2-5-5-6 in D16S3093/D16S685/D16S690/D16S3081/D16S3080 D16S411/D16S3136/D16S3112/D16S3057 were affected by PKC. There were no causative mutation in CACNG3, IL4R and ABCC11 genes.

CONCLUSIONS

The culprit gene for PKC was located in approximately 19.34 cM region between 16p12.1-q13, and CACNG3, IL4R and ABCC11 were all ruled out as the cause.

Mouvements anormaux paroxystiques non épileptiques de l'enfant

Paroxysmal movement disorders are not uncommon in childhood, but are probably under-recognised. Paroxysmal movement disorders are a distinctive group of disorders that represents various clinical situations, characterised by intermittent and episodic disturbances of movement. Diagnosis relies on semiological analysis, mainly based on parental description of the manifestations; video recording (during an EEG-video monitoring or home made video) are often helpful to establish the correct diagnosis. In the large majority of the cases, paroxysmal movement disorders are benign situations. Some of them are transient, as they spontaneously stop over time (benign torticolis of infancy, paroxysmal tonic upgaze). Being familiar with these disorders will lead to accurate diagnosis, so avoiding useless investigations. Most of the time, no treatment will be required, and the families will be informed of the good prognosis.

Clinical evaluation of idiopathic paroxysmal kinesigenic dyskinesia: new diagnostic criteria

BACKGROUND

Paroxysmal kinesigenic dyskinesia (PKD) is a rare disorder characterized by short episodes of involuntary movement attacks triggered by sudden voluntary movements. Although a genetic basis is suspected in idiopathic cases, the gene has not been discovered. Establishing strict diagnostic criteria will help genetic studies.

METHODS

The authors reviewed the clinical features of 121 affected individuals, who were referred for genetic study with a presumptive diagnosis of idiopathic PKD.

RESULTS

The majority (79%) of affected subjects had a distinctive homogeneous phenotype. The authors propose the following diagnostic criteria for idiopathic PKD based on this phenotype: identified trigger for the attacks (sudden movements), short duration of attacks (<1 minute), lack of loss of consciousness or pain during attacks, antiepileptic drug responsiveness, exclusion of other organic diseases, and age at onset between 1 and 20 years if there is no family history (age at onset may be applied less stringently in those with family history). In comparing familial and sporadic cases, sporadic cases were more frequently male, and infantile convulsions were more common in the familial kindreds. Females had a higher remission rate than males. An infantile-onset group with a different set of characteristics was identified. A clear kinesigenic trigger was not elicited in all cases, antiepileptic response was not universal, and some infants had attacks while asleep.

CONCLUSIONS

The diagnosis of idiopathic paroxysmal kinesigenic dyskinesia (PKD) can be made based on historical features. The correct diagnosis has implications for treatment and prognosis, and the diagnostic scheme may allow better focus in the search for the PKD gene(s).

Channelopathy: hypothesis of a common pathophysiologic mechanism in different forms of paroxysmal dyskinesia

Paroxysmal dyskinesias are a rare heterogeneous group of neurologic disorders, characterized by transient sudden choreoathetoid or dystonic attacks without loss of consciousness. This study reports a family with six affected members in three generations, and two sporadic cases of paroxysmal dyskinesia. Familial cases of paroxysmal dyskinesia are affected by idiopathic long-lasting paroxysmal exertion-induced dyskinesia and the sporadic cases by idiopathic short-lasting paroxysmal kinesigenic dyskinesia. Familial cases also suffer from epilepsy, mainly of generalized type, with benign outcome; one sporadic case is affected by migraine. Results presented in this neurophysiologic study include electromyography, somatosensory evoked potentials by median nerve stimulation, somatosensory evoked potentials by posterior tibial nerve stimulation, motor evoked potentials by magnetic transcranial cortical stimulation, visual evoked potentials, brainstem auditory evoked potentials, blink reflex, reflex H, and electroencephalography. The clinical and neurophysiologic findings presented here suggest a condition of hyperexcitability at the muscular and brain level, perhaps as a result of an ion channel disorder, which is in agreement with reports in the literature.

[Movement disorders in childhood: classification and genetic update]

Abnormal movements are not unusual in childhood. Recent genetic progresses provide a new approach of childhood movement disorders. Several loci have been identified in paroxysmal dyskinesia, or in Gilles de la Tourette syndrome. A gene has been cloned in Hallervorden-Spatz syndrome, and a gene has recently been implicated in benign hereditary chorea. Considerable advances concern the genetic of dystonic syndromes: several chromosomal localizations have been identified, and several genes have been cloned. Genetic advances allow nosographic reclassification of some entities and offer new molecular tools for a more appropriate diagnosis. The increasing wealth of genetic knowledge will provide further insight in the understanding of abnormal movement disorders in childhood.