Targeted genomic sequencing identifies PRRT2 mutations as a cause of paroxysmal kinesigenic choreoathetosis

Long-term low-dose lamotrigine for paroxysmal kinesigenic dyskinesia: a two-year investigation of cognitive function in children

Objective

While low-dose lamotrigine has shown effectiveness in managing paroxysmal kinesigenic dyskinesia (PKD) in pediatric populations, the cognitive consequences of extended use are yet to be fully elucidated. This study seeks to assess the evolution of cognitive functions and the amelioration of attention deficit and hyperactivity disorder (ADHD) symptoms following a two-year lamotrigine treatment in children.

Methods

This investigation employed an open-label, uncontrolled trial design. Between January 2008 and December 2021, thirty-one participants, ranging in age from 6.5 to 14.1 years, were enrolled upon receiving a new diagnosis of PKD, as defined by the clinical diagnostic criteria set by Bruno in 2004. Comprehensive evaluation of PRRT2 variants and 16p11.2 microdeletion was achieved using whole-exome sequencing (WES) and bioinformatics analysis of copy number variant (CNV) for all subjects. Immediately after diagnosis, participants commenced treatment with low-dose lamotrigine. Cognitive function was assessed using the Wechsler Intelligence Scale for Children-Chinese Revised (WISC-CR) at baseline and after 2 years, with ADHD diagnoses and symptom severity simultaneously assessed by experts in accordance with the DSM-IV diagnostic criteria for ADHD and the ADHD Rating Scale-IV (ADHD-RS-IV).

Results

Initially, twelve out of 31 patients (38.7%) presented with comorbid ADHD. The latency to treatment initiation was notably longer in PKD patients with ADHD (30.75 ± 12.88 months) than in those without ADHD (11.66 ± 9.08 months), t = 4.856, p<0.001. Notably, patients with a latency exceeding 2 years exhibited a heightened risk for comorbid ADHD (OR = 4.671, P=0.015) in comparison to those with shorter latency. Out of the cohort, twenty-five patients saw the clinical trial to its completion. These individuals demonstrated a marked elevation in WISC-CR scores at the 2-year mark relative to the outset across FSIQ (baseline mean: 108.72 ± 10.45 vs 24 months: 110.56 ± 10.03, p=0.001), VIQ (baseline mean: 109.44 ± 11.15 vs 24 months: 110.80 ± 10.44, p=0.028), and PIQ domains (baseline mean: 106.52 ± 9.74 vs 24 months: 108.24 ± 9.38, p=0.012). Concurrently, a substantial mitigation was observed in ADHD inattention at 2 years compared to baseline (p<0.001), with an average total subscale scores decrement from 9.04 ± 4.99 to 6.24 ± 4.05.

Conclusion

Prolonged duration of untreated PKD in children may elevate the risk of ADHD comorbidity. Notably, following a 2-year lamotrigine regimen, enhancements were observed in both cognitive test outcomes and ADHD symptomatology.

A Curious Case of a Child With Recurrent Twisting Movements of Limbs

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by recurrent attacks of abnormal involuntary movements that are triggered by sudden movement, intention to move, or acceleration. A 10-year-old boy presented with paroxysmal, involuntary twisting movements of the left upper and lower limbs, precipitated by sudden body movements, lasting for 10-15 seconds and subsiding spontaneously. On examination, choreiform movements were observed, which were precipitated by sudden movements during some activities. The patient responded to carbamazepine with complete subsidence of the movements. The diagnosis of PKD was further confirmed by genetic testing. A high suspicion index helps in the prompt and early diagnosis of this rare entity.

The neurodevelopmental spectrum of synaptic vesicle cycling disorders

In this review, we describe and discuss neurodevelopmental phenotypes arising from rare, high penetrance genomic variants which directly influence synaptic vesicle cycling (SVC disorders). Pathogenic variants in each SVC disorder gene lead to disturbance of at least one SVC subprocess, namely vesicle trafficking (e.g. KIF1A and GDI1), clustering (e.g. TRIO, NRXN1 and SYN1), docking and priming (e.g. STXBP1), fusion (e.g. SYT1 and PRRT2) or re-uptake (e.g. DNM1, AP1S2 and TBC1D24). We observe that SVC disorders share a common set of neurological symptoms (movement disorders, epilepsies), cognitive impairments (developmental delay, intellectual disabilities, cerebral visual impairment) and mental health difficulties (autism, ADHD, psychiatric symptoms). On the other hand, there is notable phenotypic variation between and within disorders, which may reflect selective disruption to SVC subprocesses, spatiotemporal and cell-specific gene expression profiles, mutation-specific effects, or modifying factors. Understanding the common cellular and systems mechanisms underlying neurodevelopmental phenotypes in SVC disorders, and the factors responsible for variation in clinical presentations and outcomes, may translate to personalized clinical management and improved quality of life for patients and families.

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.

Levetiracetam-responsive paroxysmal exertional dyskinesia in a Welsh Terrier

A 5-and-a-half-year old, 9-kg, spayed, female Welsh Terrier presented with a 12 month history of paroxysmal exertion-induced dyskinesia (PED) characterized by recurrent episodes of involuntary hyperkinetic movements, abnormal muscle tone, and contractions triggered by exercise. A single episode occurred within 2 hours after exercise, lasted from 7 to 10 minutes, and resolved without treatment. The owner sought treatment for the dog when the episodes began to last longer (20-30 minutes), and occurred as long as 2.5 to 8 hours after exercise. Diazepam administered intranasally at the start of an episode promptly alleviated the symptoms. Maintenance therapy with levetiracetam proved effective, such that the dog was gradually returned to exercise. However, attempts to wean the dog off the drug resulted in reoccurrence. Although the pathophysiology of PED is not fully understood, the clinical presentation and the positive response to antiepileptic therapy highlight the overlap between disease pathways in epilepsy and PED in dogs.

Generation of an induced pluripotent stem cell line (ZZUi022-A) from a paroxysmal kinesigenic dyskinesia individual carrying the PRRT2 gene mutation

Paroxysmal kinesigenic dyskinesia (PKD), the most common type of paroxysmal movement disorders, is caused by mutations in PRRT2 gene. We identified an unreported PRRT2 c. 535 C > T (p. Q 1 7 9 *) pathogenic mutation in a Chinese Han family with PKD and generated an induced pluripotent stem cell (iPSC) line from a patient in the family by reprogramming fibroblasts with sendai virus. The iPSC line was characterized for genetic uniqueness, genomic integrity, pluripotency, and differentiation ability. This iPSC line will be a powerful tool to to study the molecular mechanisms underlying PKD.

The Phenotypic Spectrum of PRRT2-Associated Paroxysmal Neurologic Disorders in Childhood

Pathogenic variants in PRRT2, encoding the proline-rich transmembrane protein 2, have been associated with an evolving spectrum of paroxysmal neurologic disorders. Based on a cohort of children with PRRT2-related infantile epilepsy, this study aimed at delineating the broad clinical spectrum of PRRT2-associated phenotypes in these children and their relatives. Only a few recent larger cohort studies are on record and findings from single reports were not confirmed so far. We collected detailed genetic and phenotypic data of 40 previously unreported patients from 36 families. All patients had benign infantile epilepsy and harbored pathogenic variants in PRRT2 (core cohort). Clinical data of 62 family members were included, comprising a cohort of 102 individuals (extended cohort) with PRRT2-associated neurological disease. Additional phenotypes in the cohort of patients with benign sporadic and familial infantile epilepsy consist of movement disorders with paroxysmal kinesigenic dyskinesia in six patients, infantile-onset movement disorders in 2 of 40 individuals, and episodic ataxia after mild head trauma in one girl with bi-allelic variants in PRRT2. The same girl displayed a focal cortical dysplasia upon brain imaging. Familial hemiplegic migraine and migraine with aura were reported in nine families. A single individual developed epilepsy with continuous spikes and waves during sleep. In addition to known variants, we report the novel variant c.843G>T, p.(Trp281Cys) that co-segregated with benign infantile epilepsy and migraine in one family. Our study highlights the variability of clinical presentations of patients harboring pathogenic PRRT2 variants and expands the associated phenotypic spectrum.

Treatment of Paroxysmal Dyskinesia

Paroxysmal dyskinesia (PxD) is a heterogeneous group of syndromes characterized by recurrent attacks of abnormal movements, triggered by detectable factors, without loss of consciousness. According to the precipitating factors, they are classified as paroxysmal kinesigenic dyskinesia (PKD), paroxysmal non-kinesigenic dyskinesia (PNKD), and paroxysmal exercise-induced dystonia (PED). PxD treatment is based on the combination of nonpharmacologic and pharmacologic approaches. Pharmacologic and nonpharmacologic treatments effective for PNKD and PED also are available. In PxD refractory to conventional treatment, surgery might be an alternative therapeutic option. The course of PRRT2-PKD and MR-1-PNKD is benign, and treatment might not be needed with advancing age.

Clinical features of patients with paroxysmal kinesigenic dyskinesia, mutation screening of PRRT2 and the effects of morning draughts of oxcarbazepine

Background

The objective of this study was to summarize clinical features and PRRT2 mutations of paediatric paroxysmal kinesigenic dyskinesia (PKD) patients and observe the tolerability and effects of morning draughts of oxcarbazepine.

Methods

Twenty patients diagnosed with PKD at Children’s Hospital of Fudan University between January 2011 and December 2015 were enrolled. These patients’ medical records were reviewed. Peripheral venous blood was obtained from all enrolled patients, and polymerase chain reaction (PCR) and Sanger sequencing were used to sequence proline-rich transmembrane protein 2 (PRRT2) gene mutations. Clinical features of PKD patients with and without PRRT2 mutations were compared. All enrolled patients were treated with morning draughts of oxcarbazepine (OXC). The starting dose was 5 mg/kg·d, and the dose was increased by 5 mg/kg·d each week until attacks stopped. Effective doses and adverse effects were recorded.

Results

For all enrolled patients, dyskinesia was triggered by sudden movement. Dyskinetic movement usually involved the limbs and was bilateral; the majority of enrolled patients exhibited both dystonia and choreoathetosis. We identified PRRT2 mutations in 5 patients, including 4 familial patients and 1 sporadic patient. All 20 patients took low doses of OXC (5–20 mg/kg·d) as draughts in the morning, and dyskinesia attacks stopped in 19 patients.

Conclusions

Paediatric PKD patients have various phenotypes. PRRT2 mutations are common in familial cases. OXC taken as morning draughts can be a treatment option for paediatric PKD patients.

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.

Targeted gene capture sequencing in diagnosis of dystonia patients

BACKGROUND

Dystonia is a movement disorder with high clinical and genetic heterogeneity. Molecular diagnosis is important for an accurate diagnosis of dystonia. Targeted gene capture sequencing has been an effective method for screening multiple candidate genes simultaneously. This method, however, has been rarely reported to be used with dystonia patients.

OBJECTIVES AND METHODS

To assess the effectiveness of the targeted gene capture sequencing in dystonia, we performed custom target gene capture followed by next-generation sequencing in dystonia patients from China. Sanger sequencing was utilized to substantiate the findings. The effects of identified variants were classified according to the American College of Medical Genetics and Genomics (ACMG) standards and guidelines.

RESULTS

A total of 65 patients (34 female and 31 male) were recruited in this study. The mean age at onset was 22.7 ± 13.3 years ranging from 2 to 59 years. According to ACMG standards and guidelines, of 65 patients, 12 were identified with pathogenic variants (12/65, 18.5%) in gene TOR1A, PANK2 or ATP1A3, and another four were identified with likely-pathogenic variants (4/65, 6.2%) in gene PRRT2, GCH1 or THAP1. In total, 24.6% of patients in this cohort were detected to have a genetic cause of dystonia. Another four patients (4/65, 6.2%) were identified with variants which were considered to be VUS (Variants of Uncertain Significance) in gene SGCE, TH, ANO3 and ATP1A3 respectively. The most common detected gene was TOR1A, known to be causative for DYT1 (8/65, 12.3%).

CONCLUSIONS

The study demonstrates that targeted gene capture sequencing is an effective tool for identifying the genetic cause of heterogeneous dystonia patients.

Aberrant transcriptional networks in step-wise neurogenesis of paroxysmal kinesigenic dyskinesia-induced pluripotent stem cells

Paroxysmal kinesigenic dyskinesia (PKD) is an episodic movement disorder with autosomal-dominant inheritance and marked variability in clinical manifestations.

Proline-rich transmembrane protein 2 (PRRT2) has been identified as a causative gene of PKD, but the molecular mechanism underlying the pathogenesis of PKD still remains a mystery. The phenotypes and transcriptional patterns of the PKD disease need further clarification. Here, we report the generation and neural differentiation of iPSC lines from two familial PKD patients with c.487C>T (p. Gln163X) and c.573dupT (p. Gly192Trpfs*8) PRRT2 mutations, respectively. Notably, an extremely lower efficiency in neural conversion from PKD-iPSCs than control-iPSCs is observed by a step-wise neural differentiation method of dual inhibition of SMAD signaling. Moreover, we show the high expression level of PRRT2 throughout the human brain and the expression pattern of PRRT2 in other human tissues for the first time. To gain molecular insight into the development of the disease, we conduct global gene expression profiling of PKD cells at four different stages of neural induction and identify altered gene expression patterns, which peculiarly reflect dysregulated neural transcriptome signatures and a differentiation tendency to mesodermal development, in comparison to control-iPSCs. Additionally, functional and signaling pathway analyses indicate significantly different cell fate determination between PKD-iPSCs and control-iPSCs. Together, the establishment of PKD-specific in vitro models and the illustration of transcriptome features in PKD cells would certainly help us with better understanding of the defects in neural conversion as well as further investigations in the pathogenesis of the PKD disease.

Proline-rich transmembrane protein 2-negative paroxysmal kinesigenic dyskinesia: Clinical and genetic analyses of 163 patients

BACKGROUND

Paroxysmal kinesigenic dyskinesia is the most common type of paroxysmal dyskinesia. Approximately half of the cases of paroxysmal kinesigenic dyskinesia worldwide are attributable to proline-rich transmembrane protein 2 mutations.

OBJECTIVE

The objective of this study was to investigate potential causative genes and clinical characteristics in proline-rich transmembrane protein 2-negative patients with paroxysmal kinesigenic dyskinesia.

METHODS

We analyzed clinical manifestations and performed exome sequencing in a cohort of 163 proline-rich transmembrane protein 2-negative probands, followed by filtering data with a paroxysmal movement disorders gene panel. Sanger sequencing, segregation analysis, and phenotypic reevaluation were used to substantiate the findings.

RESULTS

The clinical characteristics of the enrolled 163 probands were summarized. A total of 39 heterozygous variants were identified, of which 33 were classified as benign, likely benign, and uncertain significance. The remaining 6 variants (3 novel, 3 documented) were pathogenic and likely pathogenic. Of these, 3 were de novo (potassium calcium-activated channel subfamily M alpha 1, c.1534A>G; solute carrier family 2 member 1, c.418G>A; sodium voltage-gated channel alpha subunit 8, c.3640G>A) in 3 sporadic individuals, respectively. The other 3 (paroxysmal nonkinesiogenic dyskinesia protein, c.956dupA; potassium voltage-gated channel subfamily A member 1, c.765C>A; Dishevelled, Egl-10, and Pleckstrin domain containing 5, c.3311C>T) cosegregated in 3 families. All 6 cases presented with typical paroxysmal kinesigenic dyskinesia characteristics, except for the Dishevelled, Egl-10, and Pleckstrin domain containing 5 family, where the proband's mother had abnormal discharges in her temporal lobes in addition to paroxysmal kinesigenic dyskinesia episodes.

CONCLUSIONS

Our findings extend the genotypic spectrum of paroxysmal kinesigenic dyskinesia and establish the associations between paroxysmal kinesigenic dyskinesia and genes classically related to other paroxysmal movement disorders. De novo variants might be a cause of sporadic paroxysmal kinesigenic dyskinesia. © 2018 International Parkinson and Movement Disorder Society.

PRRT2 mutations in a cohort of Chinese families with paroxysmal kinesigenic dyskinesia and genotype-phenotype correlation reanalysis in literatures

PURPOSE OF THE STUDY

Though rare, children are susceptible to paroxysmal dyskinesias such as paroxysmal kinesigenic dyskinesia, and infantile convulsions and choreoathetosis. Recent studies showed that the cause of paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis could be proline-rich transmembrane protein 2 (PRRT2) gene mutations.

MATERIAL AND METHODS

This study analysed PRRT2 gene mutations in 51 families with paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis by direct sequencing. In particular, we characterize the genotype-phenotype correlation between age at onset and the types of PRRT2 mutations in all published cases.

RESULTS

Direct sequencing showed that 12 out of the 51 families had three different pathogenic mutations (c.649dupC, c.776dupG, c.649C>T) in the PRRT2 gene. No significant difference of age at onset between the patients with and without PRRT2 mutations was found in this cohort of patients. A total of 97 different PRRT2 mutations have been reported in 87 studies till now. The PRRT2 mutation classes are wide, and most mutations are frameshift mutations but the most common mutation remains c.649dupC. Comparisons of the age at onset in paroxysmal kinesigenic dyskinesia or infantile convulsions patients with different types of mutations showed no significant difference.

CONCLUSIONS

This study expands the clinical and genetic spectrums of Chinese patients with paroxysmal kinesigenic dyskinesia and infantile convulsions and choreoathetosis. No clear genotype-phenotype correlation between the age at onset and the types of mutations has been determined.

Mutation Analysis of MR-1, SLC2A1, and CLCN1 in 28 PRRT2-negative Paroxysmal Kinesigenic Dyskinesia Patients

BACKGROUND

Paroxysmal kinesigenic dyskinesia (PKD) is the most common subtype of paroxysmal dyskinesias and is caused by mutations in PRRT2 gene. The majority of familial PKD was identified to harbor PRRT2 mutations. However, over two-third of sporadic PKD patients did not carry anyPRRT2 mutation, suggesting an existence of additional genetic mutations or possible misdiagnosis due to clinical overlap.

METHODS

A cohort of 28 Chinese patients clinically diagnosed with sporadic PKD and excluded PRRT2 mutations were recruited. Clinical features were evaluated, and all subjects were screened for MR-1, SLC2A1, and CLCN1 genes, which are the causative genes of paroxysmal nonkinesigenic dyskinesia (PNKD), paroxysmal exertion-induced dyskinesia, and myotonia congenita (MC), respectively. In addition, 200 genetically matched healthy individuals were recruited as controls.

RESULTS

A total of 16 genetic variants including 4 in MR-1 gene, 8 in SLC2A1 gene, and 4 in CLCN1 gene were detected. Among them, SLC2A1 c.363G>A mutation was detected in one case, and CLCN1 c.1205C>T mutation was detected in other two cases. Neither of them was found in 200 controls as well as 1000 Genomes database and ExAC database. Both mutations were predicted to be pathogenic by SIFT and PolyPhen2. The SLC2A1 c.363G>A mutation was novel.

CONCLUSIONS

The phenotypic overlap may lead to the difficulty in distinguishing PKD from PNKD and MC. For those PRRT2- negative PKD cases, screening of SLC2A1 and CLCN1 genes are useful in confirming the diagnosis.

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.

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 next generation of target capture technologies - large DNA fragment enrichment and sequencing determines regional genomic variation of high complexity

BACKGROUND

The ability to capture and sequence large contiguous DNA fragments represents a significant advancement towards the comprehensive characterization of complex genomic regions. While emerging sequencing platforms are capable of producing several kilobases-long reads, the fragment sizes generated by current DNA target enrichment technologies remain a limiting factor, producing DNA fragments generally shorter than 1 kbp. The DNA enrichment methodology described herein, Region-Specific Extraction (RSE), produces DNA segments in excess of 20 kbp in length. Coupling this enrichment method to appropriate sequencing platforms will significantly enhance the ability to generate complete and accurate sequence characterization of any genomic region without the need for reference-based assembly.

RESULTS

RSE is a long-range DNA target capture methodology that relies on the specific hybridization of short (20-25 base) oligonucleotide primers to selected sequence motifs within the DNA target region. These capture primers are then enzymatically extended on the 3'-end, incorporating biotinylated nucleotides into the DNA. Streptavidin-coated beads are subsequently used to pull-down the original, long DNA template molecules via the newly synthesized, biotinylated DNA that is bound to them. We demonstrate the accuracy, simplicity and utility of the RSE method by capturing and sequencing a 4 Mbp stretch of the major histocompatibility complex (MHC). Our results show an average depth of coverage of 164X for the entire MHC. This depth of coverage contributes significantly to a 99.94 % total coverage of the targeted region and to an accuracy that is over 99.99 %.

CONCLUSIONS

RSE represents a cost-effective target enrichment method capable of producing sequencing templates in excess of 20 kbp in length. The utility of our method has been proven to generate superior coverage across the MHC as compared to other commercially available methodologies, with the added advantage of producing longer sequencing templates amenable to DNA sequencing on recently developed platforms. Although our demonstration of the method does not utilize these DNA sequencing platforms directly, our results indicate that the capture of long DNA fragments produce superior coverage of the targeted region.

Lamotrigine monotherapy for paroxysmal kinesigenic dyskinesia in children

PURPOSE

To evaluate the efficacy and tolerability of lamotrigine monotherapy in children with paroxysmal kinesigenic dyskinesia.

METHOD

A sample of eighteen children aged between 2 years old and 13 years old who fulfilled the diagnostic criteria from January 2008 to December 2014 was enrolled, they received video electroencephalography, brain image scans and proline-rich transmembrane protein 2 genetic tests. Children with known or suspected diseases which would cause secondary paroxysmal kinesigenic dyskinesia were excluded. The initial dosage of lamotrigine was 6.25 mg, and it was gradually increased every week until attacks were controlled. Patients entered the maintenance dose phase upon reaching the effective dosage, and by being attack free at two consecutive outpatient visits. They were followed up for a couple of years until December 2014.

RESULTS

By the end of the 4th week, the attack-free rate reached 100% among all the patients. During the maintenance dose phase, 16 patients remained attack free, 2 patients received additional drug due to attack relapses when they entered puberty. Three patients had relapses because of non-compliance to the therapy, but they became attack free as soon as they re-started the medicine. The mean daily dosage was 26.4 mg (range 6.25-50). Definite adverse effect related to the drug was not reported in follow up.

CONCLUSION

LTG monotherapy is effective and well tolerated for PKD in children.

Clinical and genetic features of paroxysmal kinesigenic dyskinesia in Italian patients

BACKGROUND

Paroxysmal Kinesigenic Dyskinesia (PKD, OMIM 128200) is the most common type of autosomal dominant Paroxysmal Dyskinesias characterized by attacks of dystonia and choreoathetosis triggered by sudden movements. Recently PRRT2, encoding proline-rich transmembrane protein 2, has been described as the most frequent causative gene for PKD.

METHODS

We studied the incidence of PRRT2 mutations in a cohort of 16 PKD patients and their relatives for a total of 39 individuals.

RESULTS

We identify mutations in 10/16 patients and 23 relatives. In 27/33 the mutation was the c.insC649 p.Arg217Profs*8. In 6 individuals from 3 families we found three new mutations: c.insT27 p.Ser9*, c.G967A p.Gly323Arg and c.delCA215_216 p.Thr72Argfs*62. Family history was positive in 9 patients. The mean age of onset was 10 years. Attacks lasted from a few seconds to 1 min and ranged from several per day to some per week, and were generalised in all patients. The main distinctive features of mutation-negative patients were the sporadic occurrence, the absence of association with epilepsy or EEG abnormalities and the poor response to Carbamazepine or other antiepileptic agents.

CONCLUSIONS

We report the first cohort of Italian patients mutated in PRRT2 and we confirm that this is the most frequent gene involved in PKD.

Urine-derived induced pluripotent stem cells as a modeling tool for paroxysmal kinesigenic dyskinesia

Paroxysmal kinesigenic dyskinesia (PKD) is a monogenic movement disorder with autosomal dominant inheritance. We previously identified the proline-rich transmembrane protein 2 (PRRT2) as a causative gene of PKD. However, the pathogenesis of PKD remains largely unknown so far. In addition, applicable modeling tools to investigate the underlying mechanisms of PKD are still lacking. The combination of disease-specific human induced pluripotent stem cells (iPSCs) and directed cell differentiation offers an ideal platform for disease modeling. In this study, we generated two iPSC lines from the renal epithelial cells of one PKD patient with the hotspot c.649dupC mutation (PKD-iPSCs). These cell lines were positive for alkaline phosphatase Nanog, Tra-1-80, Tra-1-60, SSEA-3 and SSEA-4. Teratomas with three blastoderms including ectoderm, mesoderm, and endoderm were obtained two months after injection of PKD-iPSCs into NOD/SCID mice. The expression of PRRT2 mRNA was decreased in PKD-iPSCs compared with that of the control iPSCs. Furthermore, PKD-iPSCs possessed the differentiation potential of functional glutamatergic, dopaminergic and motor neurons in vitro. Electrophysiological examinations revealed that the current densities of fast activated and deactivated sodium channels as well as voltage gated potassium channels were not different between the neurons from PKD-iPSCs and control iPSCs. Thus, PKD-iPSCs are a feasible modeling tool to investigate the pathogenic mechanisms of PKD.

Summary: This is the first report of urinary cell-induced pluripotent stem cells being used as resources for investigation of the pathological mechanisms of paroxysmal kinesigenic dyskinesia.

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.

Paroxysmal kinesigenic dyskinesia: Clinical and genetic analyses of 110 patients

OBJECTIVE

We aimed to investigate the clinical and genetic features of paroxysmal kinesigenic dyskinesia (PKD) in a large population and to analyze the genotype-phenotype correlation of PKD.

METHODS

We analyzed clinical manifestations and conducted PRRT2 screening in 110 patients with PKD. Clinical data were compared between 91 probands with and without PRRT2 mutations.

RESULTS

Among the enrolled participants (45 from 26 families, 65 sporadic cases), 8 PRRT2 mutations were detected in 20 PKD families (76.9%) and 14 sporadic cases (21.5%), accounting for 37.4% (34/91) of the study population. Five mutations (c.649dupC, c.649delC, c.487C>T, c.573dupT, c.796C>T) were already reported, while 3 mutations (c.787C>T, c.797G>A, c.931C>T) were undocumented. A patient harboring a homozygous c.931C>T mutation was shown to have inherited the mutation via uniparental disomy. Compared with non-PRRT2 mutation carriers, the PRRT2 mutation carriers were younger at onset, experienced longer attacks, and tended to present with complicated PKD, combined phenotypes of dystonia and chorea, and a positive family history. A good response was shown in 98.4% of the patients prescribed with carbamazepine.

CONCLUSIONS

PRRT2 mutations are common in patients with PKD and are significantly associated with an earlier age at onset, longer duration of attacks, a complicated form of PKD, combined phenotypes of dystonia and chorea, and a tendency for a family history of PKD. A patient with uniparental disomy resulting in a homozygous c.931C>T mutation is identified in the present study. Carbamazepine is the first-choice drug for patients with PKD, but an individualized treatment regimen should be developed.

Characteristics of patients with benign partial epilepsy in infancy without PRRT2 mutations

Mutations in the proline-rich transmembrane protein 2 gene (PRRT2) are known to cause clinical symptoms of paroxysmal kinesigenic dyskinesia (PKD), benign partial epilepsy in infancy (BPEI), and infantile convulsions with choreoathetosis (ICCA) syndrome; however, not all patients with BPEI have PRRT2 mutations, and the genetic backgrounds for such patients are still unknown. To characterize BPEI patients without PRRT2 mutations, we analyzed unrelated 63 patients with BPEI. Sanger sequencing identified PRRT2 mutations in 33 probands (52%). The most common insertion, c.649dup, was identified in 28 probands. Two novel truncation mutations, c.232dup and c.503_504del were identified independently. 16p11.2 microdeletion was not detected in patients without PRRT2 mutations. PRRT2 mutation detection rates were 21/31 (68%) and 12/32 (38%) in probands who were positive or negative for family history, respectively, indicating a significant difference between the two groups. In this study, 20 probands with BPEI were negative for family history of BPEI and negative for PRRT2 mutation. BPEI in these probands may be due to complex genetic predispositions. Because the possibility remains that a second gene contributes to BPEI, further studies are necessary in patients with BPEI but no PRRT2 mutation, especially in Asian people.

PRRT2 Mutant Leads to Dysfunction of Glutamate Signaling

Paroxysmal kinesigenic choreoathetosis (PKC) is an inherited disease of the nervous system. We previously identified PRRT2 as the causative gene of PKC. However, as little is known about the function of PRRT2, elucidating its function will benefit not only PKC studies, but also many other related disorders. Here, we reveal higher levels of glutamate in the plasma of PKC patients and the culture medium of neurons following knock-out Prrt2 expression. Using double immunostaining assays we confirm Prrt2 is located at the glutamatergic neurons in accordance with its function. Our co-immunoprecipitation assays reveal mutant PRRT2 interferes with SNAP25 and GRIA1 interactions, respectively. Furthermore, using live-labeling techniques, we confirmed co-transfection with mutant PRRT2 caused an increase in GRIA1 distribution on the cell surface. Therefore, our results suggest that mutant PRRT2, probably through its weakened interaction with SNAP25, affects glutamate signaling and glutamate receptor activity, resulting in the increase of glutamate release and subsequent neuronal hyperexcitability.

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.

Paroxysmal kinesigenic dyskinesia and myotonia congenita in the same family: coexistence of a PRRT2 mutation and two CLCN1 mutations

Paroxysmal kinesigenic dyskinesia (PKD) and myotonia congenita (MC) are independent disorders that share some clinical features. We aimed to investigate the sequences of PRRT2 and CLCN1 in a proband diagnosed with PKD and suspected MC. Clinical evaluation and auxiliary examinations were performed. Direct sequencing of the entire coding regions of the PRRT2 and CLCN1 genes was conducted. Haplotype analysis confirmed the relationships among the family members. The proband suffered choreoathetosis attacks triggered by sudden movements, and lower-limb weakness and stiffness that worsened in cold weather. Carbamazepine monotherapy completely controlled his choreoathetosis and significantly relieved his limb weakness and stiffness. His father, when young, had similar limb stiffness, while his mother and brother were asymptomatic. Genetic analysis revealed that the proband and his father harbored a PRRT2 c.649dupC mutation, and CLCN1 c.1723C>T and c.2492A>G mutations. His brother carried only the two CLCN1 mutations. None of these mutations were identified in his mother and 150 unrelated controls. This is the first report showing the coexistence of PRRT2 and CLCN1 mutations. Our results also indicate that both the PRRT2 and CLCN1 genes need to be screened if we fail to identify PRRT2 mutations in PKD patients or CLCN1 mutations in MC patients.

Genetics in dystonia: an update

The past year has been extremely successful with regard to the genetics of dystonia, with the identification of four new dystonia genes (CIZ1, ANO3, GNAL, and TUBB4A). This progress was primarily achieved because of the application of a new technology, next-generation DNA sequencing, which allows rapid and comprehensive assessment of a patient's genome. In addition, a combination of next-generation and traditional Sanger sequencing has expanded the phenotypic spectrum associated with some of the dystonia plus (ATP1A3) and paroxysmal (PRRT2) loci. This article reviews the newly identified genes and phenotypes and discusses the future applications of next-generation sequencing to dystonia research.

Successful control with carbamazepine of family with paroxysmal kinesigenic dyskinesia of PRRT2 mutation

Paroxysmal kinesigenic dyskinesia (PKD), a rare paroxysmal movement disorder often misdiagnosed as epilepsy, is characterized by recurrent, brief dyskinesia attacks triggered by sudden voluntary movement. Pathophysiological mechanism of PKD remains not well understood. Ion channelopathy has been suggested, since the disease responds well to ion channel blockers. Mutations in proline-rich transmembrane protein 2 (PRRT2) were recently identified in patients with familial PKD. To extend these genetic reports, we studied a family with clinical manifestations of familial PKD responding well to low dose carbamazepine. Therapeutic dose ranged from 1.5 to 2.0 mg/ kg/day, below that in seizure control. One insertion mutation c.649_650insC (p.P217fsX7) was identified in three patients of the family. This study avers PRRT2’s high sensitivity for PKD phenotype. Identification of genes underlying pathogenesis will enhance diagnosis and treatment. Function of PRRT2 and its role in PKD warrant further investigation.

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.

Clinical manifestations in paroxysmal kinesigenic dyskinesia patients with proline-rich transmembrane protein 2 gene mutation

Background and Purpose

Given the diverse phenotypes including combined non-dyskinetic symptoms in patients harboring mutations of the gene encoding proline-rich transmembrane protein 2 (PRRT2), the clinical significance of these mutations in paroxysmal kinesigenic dyskinesia (PKD) is questionable. In this study, we investigated the clinical characteristics of PKD patients with PRRT2 mutations.

Methods

Familial and sporadic PKD patients were enrolled and PRRT2 gene sequencing was performed. Demographic and clinical data were compared between PKD patients with and without a PRRT2 mutation.

Results

Among the enrolled PKD patients (8 patients from 5 PKD families and 19 sporadic patients), PRRT2 mutations were detected in 3 PKD families (60%) and 2 sporadic cases (10.5%). All familial patients with a PRRT2 gene mutation had the c.649dupC mutation, which is the most commonly reported mutation. Two uncommon mutations (c.649delC and c.629dupC) were detected only in the sporadic cases. PKD patients with PRRT2 mutation were younger at symptom onset and had more non-dyskinetic symptoms than those without PRRT2 mutation. However, the characteristics of dyskinetic movement did not differ between the two groups.

Conclusions

This is the first study of PRRT2 mutations in Korea. The presence of a PRRT2 mutation was more strongly related to familial PKD, and was clinically related with earlier age of onset and common non-dyskinetic symptoms in PKD patients.

Mutation analysis of PRRT2 in two Chinese BFIS families and nomenclature of PRRT2 related paroxysmal diseases

Benign familial infantile seizure (BFIS) and paroxysmal kinesigenic dyskinesia (PKD) are autosomal-dominant inherited self-limited neurological disorders. BFIS is characterized by clusters of epileptic seizures in infancy while, in some cases, infantile seizures and adolescent-onset paroxysmal kinesigenic choreoathetosis co-occurred, which is called infantile convulsions and choreoathetosis (ICCA) syndrome. We and other researchers have reported the proline-rich transmembrane protein 2 (PRRT2) as the causative gene of PKD. We and our collaborators also identified PRRT2 mutations in ICCA and other phenotypes. Here we collected two BFIS families of Chinese Han origin. The linkage analysis has mapped the BFIS-causing locus to 16p12.1-q12.2, where PRRT2 is located. We then performed mutation analysis of PRRT2 by direct sequencing and identified c.649-650insC mutation in all BFIS patients. We also noticed that paroxysmal diseases (such as BFIS, PKD and ICCA) with PRRT2 mutations, instead of other forms, share some characteristics like being responded well to anti-epiletic treatment, we thus suggest to name them as PRRT2-related paroxysmal diseases (PRPDs) in order to assist clinical diagnosis and treatment.

Episodic neurologic disorders: syndromes, genes, and mechanisms

Many neurologic diseases cause discrete episodic impairment in contrast with progressive deterioration. The symptoms of these episodic disorders exhibit striking variety. Herein we review what is known of the phenotypes, genetics, and pathophysiology of episodic neurologic disorders. Of these, most are genetically complex, with unknown or polygenic inheritance. In contrast, a fascinating panoply of episodic disorders exhibit Mendelian inheritance. We classify episodic Mendelian disorders according to the primary neuroanatomical location affected: skeletal muscle, cardiac muscle, neuromuscular junction, peripheral nerve, or central nervous system (CNS). Most known Mendelian mutations alter genes that encode membrane-bound ion channels. These mutations cause ion channel dysfunction, which ultimately leads to altered membrane excitability as manifested by episodic disease. Other Mendelian disease genes encode proteins essential for ion channel trafficking or stability. These observations have cemented the channelopathy paradigm, in which episodic disorders are conceptualized as disorders of ion channels. However, we expand on this paradigm to propose that dysfunction at the synaptic and neuronal circuit levels may underlie some episodic neurologic entities.

The genetics of dystonia: new twists in an old tale

Dystonia is a common movement disorder seen by neurologists in clinic. Genetic forms of the disease are important to recognize clinically and also provide valuable information about possible pathogenic mechanisms within the wider disorder. In the past few years, with the advent of new sequencing technologies, there has been a step change in the pace of discovery in the field of dystonia genetics. In just over a year, four new genes have been shown to cause primary dystonia (CIZ1, ANO3, TUBB4A and GNAL), PRRT2 has been identified as the cause of paroxysmal kinesigenic dystonia and other genes, such as SLC30A10 and ATP1A3, have been linked to more complicated forms of dystonia or new phenotypes. In this review, we provide an overview of the current state of knowledge regarding genetic forms of dystonia—related to both new and well-known genes alike—and incorporating genetic, clinical and molecular information. We discuss the mechanistic insights provided by the study of the genetic causes of dystonia and provide a helpful clinical algorithm to aid clinicians in correctly predicting the genetic basis of various forms of dystonia.

Genetic analysis of PRRT2 for benign infantile epilepsy, infantile convulsions with choreoathetosis syndrome, and benign convulsions with mild gastroenteritis

PURPOSE

PRRT2 mutations were recently identified in benign familial infantile epilepsy (BFIE) and infantile convulsions with paroxysmal choreoathetosis (ICCA) but no abnormalities have so far been identified in their phenotypically similar seizure disorder of benign convulsions with mild gastroenteritis (CwG), while mutations in KCNQ2 and KCNQ3 have been recognized in benign familial neonatal epilepsy (BFNE). The aim of this study was to identify PRRT2 mutations in infantile convulsions in Asian families with BFIE and ICCA, CwG and BFNE.

METHODS

We recruited 26 unrelated Japanese affected with either BFIE or non-familial benign infantile seizures and their families, including three families with ICCA. A total of 17 Japanese and Taiwanese with CwG, 50 Japanese with BFNE and 96 healthy volunteers were also recruited. Mutations of PRRT2 were sought using direct sequencing.

RESULTS

Heterozygous truncation mutation (c.649dupC) was identified in 15 of 26 individuals with benign infantile epilepsy (52.1%). All three families of ICCA harbored the same mutation (100%). Another novel mutation (c.1012+2dupT) was found in the proband of a family with BFIE. However, no PRRT2 mutation was found in either CwG or BFNE.

CONCLUSIONS

The results confirm that c.649dupC, a truncating mutation of PRRT2, is a hotspot mutation resulting in BFIE or ICCA regardless of the ethnic background. In contrast, PRRT2 mutations do not seem to be associated with CwG or BFNE. Screening for PRRT2 mutation might be useful in early-stage differentiation of BFIE from CwG.

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.

Altered intrinsic brain activity in patients with paroxysmal kinesigenic dyskinesia by PRRT2 mutation: altered brain activity by PRRT2 mutation

The proline-rich transmembrane protein 2 (PRRT2) gene has been recently identified as a causative gene of paroxysmal kinesigenic dyskinesia (PKD), with an insertion mutation c.649_650insC (p.P217fsX7) reported as the most common mutation. However, the pathogenic mechanism of the mutation of PRRT2 remains largely unknown. Resting-state functional magnetic resonance imaging is a promising approach to assess cerebral function and reveals underlying functional changes. Resting-state functional magnetic resonance imaging was performed in 4 Chinese PKD patients with p.P217fsX7 mutation, 6 Chinese PKD patients without the mutation, and 10 healthy control subjects. Voxel-based analysis was used to characterize alterations in the amplitude of low-frequency fluctuation (ALFF). When compared with the healthy control subjects, both groups of PKD patients showed alterations in spontaneous brain activities within cortical-basal ganglia circuitry. Besides, the group of patients with p.P217fsX7 mutation also exhibited increased ALFF in the right postcenral gyrus and right rolandic operculum area, while the alteration of ALFF in group of patients without the mutation additionally involved the middle orbitofrontal cortex. Direct comparative analysis between these two patient groups revealed significantly increased ALFF in the right postcentral gyrus in the group with p.P217fsX7 mutation. Increased spontaneous brain activity in the cortical-basal ganglia circuitry, especially in the motor preparation areas, is a common pathophysiology in PKD. Differences in the spatial patterns of increased ALFF between patients with and those without the mutation might reflect the distinct pathological mechanism resulting from PRRT2 mutation.