The PRRT2 mutation c.649dupC is the so far most frequent cause of benign familial infantile convulsions

PRRT2 variants and effectiveness of various antiepileptic drugs in self-limited familial infantile epilepsy

PURPOSE

Self-limited familial infantile epilepsy (SFIE) is largely associated with variants in proline-rich transmembrane protein 2 (PRRT2). However, the detailed phenotype-genotype correlations are unclear, along with the efficacy of various antiepileptic drugs in the treatment of this epilepsy syndrome. In this study, we analysed the PRRT2 variants associated with SFIE in Chinese patients, and the efficacy of different antiepileptic drugs prescribed during follow-up.

METHODS

We retrospectively included 20 patients diagnosed with SFIE and reviewed their clinical characteristics, genetic variants, and treatment responses.

RESULTS

Eighteen of the 20 (90%) patients harboured the common heterozygous variant of PRRT2 c.649dupC p.(Arg217fs). One patient had two heterozygous variants of PRRT2, c.640G>C p.(Ala214Pro) and c.955G>T p.(Val319Leu), and the other patient harboured a novel c.606delA (p.Pro203Hisfs) variant. Nine patients who had first-line treatment of oxcarbazepine (OXC) became seizure-free. However, initial treatment with levetiracetam (LEV) or sodium valproate (VPA) in eight and three patients, respectively, was not effective even after increasing the dosage, and seizure-free status was only achieved after changing the treatment to OXC. The treatment responses suggested a significant difference (P < 0.001) between OXC and other anti-epileptic drugs.

CONCLUSION

OXC as a sodium channel blocker may have a better effect than LEV and VPA in the treatment of PRRT2-associated SFIE. PRRT2 variants may be used as a biomarker to help select antiepileptic drugs for SFIE.

Different experiences of two PRRT2-associated self-limited familial infantile epilepsy

To analyze the clinical characteristics and PRRT2 gene mutation of self-limited familial infantile epilepsy and evaluate the treatment responses of different antiepileptic drugs in self-limited familial infantile epilepsy. We reviewed the clinical feature and genetic mutation results and treatment responses of two sibling sisters. They were detected with the PRRT2 gene mutation through Sanger sequencing. Elder sister was treated with oxcarbazepine oral suspension, while younger sister was treated with levetiracetam oral solution. The two sibling sisters exhibited PRRT2 heterozygous mutation inherited from their mother in c.649dupC p.(Arg217fs). Oxcarbazepine oral suspension had an immediate effect on the elder sister who was treated with it. However, levetiracetam oral solution had no effect on younger sister even though the dose was increased, but she got seizure-free after turning to oxcarbazepine oral suspension. Oxcarbazepine, which plays the mechanism of the sodium channel blockers, has a more significant effect than levetiracetam, which has no mechanism of the sodium channel blockers in self-limited familial infantile epilepsy. The PRRT2 gene of infantile epileptic patients with a family history of infantile convulsions or paroxysmal kinesigenic dyskinesia(PKD) could be detected by sanger sequencing and a biomarker to select antiepileptic drugs which play the mechanism of the sodium channel blockers could be utilized.

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.

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.

Mutation screening of the PRRT2 gene for benign epilepsy with centrotemporal spikes in Chinese mainland population

Proline-rich transmembrane protein 2 gene (PRRT2) mutations are reported to cause common paroxysmal neurological disorders and show a remarkable pleiotropy. Benign epilepsy with centrotemporal spikes (BECTS) is considered to be the most common epilepsy syndrome in childhood. It is placed among the idiopathic localization related epilepsies. Recently, it was reported that a girl with a PRRT2 mutation c.649_650insC developed infantile focal epilepsy with bilateral spikes which resembled the rolandic spikes. Hereby we performed a comprehensive genetic mutation screening of PRRT2 gene in a cohort of 53 sporadic BECTS patients. None of the 53 sporadic BECTS patients and other 250 controls carried mutations including c.649_650insC in PRRT2. Our data indicated that the PRRT2 mutations might most likely not be associated with BECTS in Chinese mainland population.

Neurodegeneration in a Drosophila model of adrenoleukodystrophy: the roles of the Bubblegum and Double bubble acyl-CoA synthetases

Debilitating neurodegenerative conditions with metabolic origins affect millions of individuals worldwide. Still, for most of these neurometabolic disorders there are neither cures nor disease-modifying therapies, and novel animal models are needed for elucidation of disease pathology and identification of potential therapeutic agents. To date, metabolic neurodegenerative disease has been modeled in animals with only limited success, in part because existing models constitute analyses of single mutants and have thus overlooked potential redundancy within metabolic gene pathways associated with disease. Here, we present the first analysis of a very-long-chain acyl-CoA synthetase (ACS) double mutant. We show that the Drosophila bubblegum(bgm) and double bubble(dbb) genes have overlapping functions, and that the consequences of double knockout of both bubblegum and double bubble in the fly brain are profound, affecting behavior and brain morphology, and providing the best paradigm to date for an animal model of adrenoleukodystrophy (ALD), a fatal childhood neurodegenerative disease associated with the accumulation of very-long-chain fatty acids. Using this more fully penetrant model of disease to interrogate brain morphology at the level of electron microscopy, we show that dysregulation of fatty acid metabolism via disruption of ACS function in vivois causal of neurodegenerative pathologies that are evident in both neuronal cells and their supporting cell populations, and leads ultimately to lytic cell death in affected areas of the brain. Finally, in an extension of our model system to the study of human disease, we describe our identification of an individual with leukodystrophy who harbors a rare mutation in SLC27a6(encoding a very-long-chain ACS), a human homolog of bgm and dbb.

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.

Primary and secondary dystonic syndromes: an update

PURPOSE OF REVIEW

The dystonias are a common but complex group of disorders that show considerable variation in cause and clinical presentation. The purpose of this review is to highlight the most important discoveries and insights from across the field over the period of the past 18 months.

RECENT FINDINGS

Five new genes for primary dystonia (PRRT2, CIZ1, ANO3, TUBB4A and GNAL) have made their appearance in the literature. New subtypes of neuronal brain iron accumulation have been delineated and linked to mutations in C19orf12 and WDR45, while a new treatable form of dystonia with brain manganese deposition related to mutations in SLC30A10 has been described. At the same time, the phenotypes of other forms of dystonic syndromes have been expanded or linked together. Finally, there has been increasing recognition of both the extramotor phenotype in dystonia and the part played by the cerebellum in its pathophysiology.

SUMMARY

Recently, there has been unprecedented change in the scientific landscape with respect to the cause of various dystonic syndromes that is likely to make a direct impact on clinical practice in the near future. Understanding the genetic cause of these syndromes and the often wide phenotypic variation in their presentations will improve diagnosis and treatment. With time, these discoveries may also lead to much-needed progress in elucidating the underlying pathophysiology of dystonia.

Phenotypes and PRRT2 mutations in Chinese families with benign familial infantile epilepsy and infantile convulsions with paroxysmal choreoathetosis

Background

Mutations in the PRRT2 gene have been identified as the major cause of benign familial infantile epilepsy (BFIE), paroxysmal kinesigenic dyskinesia (PKD) and infantile convulsions with paroxysmal choreoathetosis/dyskinesias (ICCA). Here, we analyzed the phenotypes and PRRT2 mutations in Chinese families with BFIE and ICCA.

Methods

Clinical data were collected from 22 families with BFIE and eight families with ICCA. PRRT2 mutations were screened using PCR and direct sequencing.

Results

Ninety-five family members were clinically affected in the 22 BFIE families. During follow-up, two probands had one seizure induced by diarrhea at the age of two years. Thirty-one family members were affected in the eight ICCA families, including 11 individuals with benign infantile epilepsy, nine with PKD, and 11 with benign infantile epilepsy followed by PKD. Two individuals in one ICCA family had PKD or ICCA co-existing with migraine. One affected member in another ICCA family had experienced a fever-induced seizure at 7 years old. PRRT2 mutations were detected in 13 of the 22 BFIE families. The mutation c.649_650insC (p.R217PfsX8) was found in nine families. The mutations c.649delC (p.R217EfsX12) and c.904_905insG (p.D302GfsX39) were identified in three families and one family, respectively. PRRT2 mutations were identified in all eight ICCA families, including c.649_650insC (p.R217PfsX8), c.649delC (p.R217EfsX12), c.514_517delTCTG (p.S172RfsX3) and c.1023A > T (X341C). c.1023A > T is a novel mutation predicted to elongate the C-terminus of the protein by 28 residues.

Conclusions

Our data demonstrated that PRRT2 is the major causative gene of BFIE and ICCA in Chinese families. Site c.649 is a mutation hotspot: c.649_650insC is the most common mutation, and c.649delC is the second most common mutation in Chinese families with BFIE and ICCA. As far as we know, c.1023A > T is the first reported mutation in exon 4 of PRRT2. c.649delC was previously reported in PKD, ICCA and hemiplegic migraine families, but we further detected it in BFIE-only families. c.904_905insG was reported in an ICCA family, but we identified it in a BFIE family. c.514_517delTCTG was previously reported in a PKD family, but we identified it in an ICCA family. Migraine and febrile seizures plus could co-exist in ICCA families.

PRRT2 mutation in Japanese children with benign infantile epilepsy

Mutations in PRRT2 genes have been identified as a major cause of benign infantile epilepsy and/or paroxysmal kinesigenic dyskinesia. We explored mutations in PRRT2 in Japanese patients with BIE as well as its related conditions including convulsion with mild gastroenteritis and benign early infantile epilepsy. We explored PRRT2 mutations in Japanese children who had had unprovoked infantile seizures or convulsion with mild gastroenteritis. The probands included 16 children with benign infantile epilepsy, 6 children with convulsions with mild gastroenteritis, and 2 siblings with benign early infantile epilepsy. In addition, we recruited samples from family members when PRRT2 mutation was identified in the proband. Statistical analyses were performed to identify differences in probands with benign infantile epilepsy according to the presence or absence of PRRT2 mutation. Among a total of 24 probands, PRRT2 mutations was identified only in 6 probands with benign infantile epilepsy. A common insertion mutation, c.649_650insC, was found in 5 families and a novel missense mutation, c.981C>G (I327M), in one. The family history of paroxysmal kinesigenic dyskinesia was more common in probands with PRRT2 mutations than in those without mutations. Our study revealed that PRRT2 mutations are common in Japanese patients with benign infantile epilepsy, especially in patients with a family history of paroxysmal kinesigenic dyskinesia.

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.

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.