PRRT2 phenotypes and penetrance of paroxysmal kinesigenic dyskinesia and infantile convulsions

A novel SLC2A1 mutation linking hemiplegic migraine with alternating hemiplegia of childhood

BACKGROUND

Hemiplegic migraine (HM) and alternating hemiplegia of childhood (AHC) are rare episodic neurological brain disorders with partial clinical and genetic overlap. Recently, ATP1A3 mutations were shown to account for the majority of AHC patients. In addition, a mutation in the SLC2A1 gene was reported in a patient with atypical AHC. We therefore investigated whether mutations in these genes may also be involved in HM. Furthermore, we studied the role of SLC2A1 mutations in a small set of AHC patients without ATP1A3 mutations.

METHODS

We screened 42 HM patients (21 familial and 21 sporadic patients) for ATP1A3 and SLC2A1 mutations. In addition, four typical AHC patients and one atypical patient with overlapping symptoms of both disorders were screened for SLC2A1 mutations.

RESULTS

A pathogenic de novo SLC2A1 mutation (p.Gly18Arg) was found in the atypical patient with overlapping symptoms of AHC and hemiplegic migraine. No mutations were found in the HM and the other AHC patients.

CONCLUSION

Screening for a mutation in the SLC2A1 gene should be considered in patients with a complex phenotype with overlapping symptoms of hemiplegic migraine and AHC.

Two novel SCN1A mutations identified in families with familial hemiplegic migraine

BACKGROUND

Familial hemiplegic migraine (FHM) is a rare monogenic subtype of migraine with aura, characterized by motor auras. The majority of FHM families have mutations in the CACNA1A and ATP1A2 genes; less than 5% of FHM families are explained by mutations in the SCN1A gene. Here we screened two Spanish FHM families for mutations in the FHM genes.

METHODS

We assessed the clinical features of both FHM families and performed direct sequencing of all coding exons (and adjacent sequences) of the CACNA1A, ATP1A2, PRRT2 and SCN1A genes.

RESULTS

FHM patients in both families had pure hemiplegic migraine with highly variable severity and frequency of attacks. We identified a novel SCN1A missense mutation p.Ile1498Met in all three tested hemiplegic migraine patients of one family. In the other family, novel SCN1A missense mutation p.Phe1661Leu was identified in six out of eight tested hemiplegic migraine patients. Both mutations affect amino acid residues that either reside in an important functional domain (in the case of Ile(1498)) or are known to be important for kinetic properties of the NaV1.1 channel (in the case of Phe(1661)).

CONCLUSIONS

We identified two mutations in families with FHM. SCN1A mutations are an infrequent but important cause of FHM. Genetic testing is indicated in families when no mutations are found in other FHM genes.

The Phenomenology of Functional (Psychogenic) Dystonia

From the very first descriptions of dystonia, there has been a lack of agreement on the differentiation of organic from functional (psychogenic) dystonia. This lack of agreement has had a significant effect on patients over the years, most particularly in the lack of access to appropriate management, whether for those with organic dystonia diagnosed as having a functional cause or vice versa. However, clinico-genetic advances have led to greater certainty about the phenomenology of organic dystonia and therefore recognition of atypical forms. The diagnosis of functional dystonia rests on recognition of its phenomenology and should not be, as far as possible, a diagnosis of exclusion. Here, we present an overview of the phenomenology of functional dystonia, concentrating on the three main phenotypic presentations: functional cranial dystonia; functional fixed dystonia; and functional paroxysmal dystonia. We hope that this review of phenomenology will aid in the positive diagnosis of functional dystonia and, through this, will lead to more rapid access to appropriate management.

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.

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.

Psychogenic paroxysmal movement disorders--clinical features and diagnostic clues

BACKGROUND

The diagnosis of psychogenic paroxysmal movement disorders (PPMD) can be challenging, in particular their distinction from the primary paroxysmal dyskinesias (PxD) remains difficult.

METHODS

Here we present a large series of 26 PPMD cases, describe their characteristics, contrast them with primary PxD and focus on their distinguishing diagnostic features.

RESULTS

Mean age at onset was 38.6 years, i.e. much later than primary PxD. Women were predominantly affected (73%). Most subjects (88.4%) had long attacks, and unlike primary PxD there was a very high within-subject variability for attack phenomenology, duration and frequency. Dystonia was the most common single movement disorder presentation, but 69.2% of the patients had mixed or complex PxD. In 50% of PPMD cases attack triggers could be identified but these were unusual for primary PxD. 42.3% of patients employed unusual strategies to alleviate or stop the attacks. Response to typical medication used for primary PxD was poor. Precipitation of the disorder due to physical or emotional life events and stressors were documented in 57.6% and 65.3% of the cases respectively. Additional interictal psychogenic signs were documented in 34.6% and further medically unexplained somatic symptoms were present in 50% of the cases. 19.2% of patients had a comorbid organic movement disorder and 26.9% had pre-existing psychiatric comorbidities.

CONCLUSION

Although the phenotypic presentation of PPMD can be highly diverse, certain clinical characteristics help in distinguishing this condition from the primary forms of PxD. Recognition is important as multidisciplinary treatment approaches led to significant improvement in most cases.

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.

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.

PRRT2-related disorders: further PKD and ICCA cases and review of the literature

Recent studies reported mutations in the gene encoding the proline-rich transmembrane protein 2 (PRRT2) to be causative for paroxysmal kinesigenic dyskinesia (PKD), PKD combined with infantile seizures (ICCA), and benign familial infantile seizures (BFIS). PRRT2 is a presynaptic protein which seems to play an important role in exocytosis and neurotransmitter release. PKD is the most common form of paroxysmal movement disorder characterized by recurrent brief involuntary hyperkinesias triggered by sudden movements. Here, we sequenced PRRT2 in 14 sporadic and 8 familial PKD and ICCA cases of Caucasian origin and identified three novel mutations (c.919C>T/p.Gln307, c.388delG/p.Ala130Profs 46, c.884G>A/p.Arg295Gln) predicting two truncated proteins and one probably damaging point mutation. A review of all published cases is also included. PRRT2 mutations occur more frequently in familial forms of PRRT2-related syndromes (80-100 %) than in sporadic cases (33-46 %) suggesting further heterogeneity in the latter. PRRT2 mutations were rarely described in other forms of paroxysmal dyskinesias deviating from classical PKD, as we report here in one ICCA family without kinesigenic triggers. Mutations are exclusively found in two exons of the PRRT2 gene at a high rate across all syndromes and with one major mutation (c.649dupC) in a mutational hotspot of nine cytosines, which is responsible for 57 % of all cases in all phenotypes. We therefore propose that genetic analysis rapidly performed in early stages of the disease is highly cost-effective and can help to avoid further unnecessary diagnostic and therapeutic interventions.

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.