Familial hemiplegic migraine with a PRRT2 mutation: Phenotypic variations and carbamazepine efficacy

The Dawn and Advancement of the Knowledge of the Genetics of Migraine

Background: Migraine is a prevalent episodic brain disorder known for recurrent attacks of unilateral headaches, accompanied by complaints of photophobia, phonophobia, nausea, and vomiting. Two main categories of migraine are migraine with aura (MA) and migraine without aura (MO). Main body: Early twin and population studies have shown a genetic basis for these disorders, and efforts have been invested since to discern the genes involved. Many techniques, including candidate-gene association studies, loci linkage studies, genome-wide association, and transcription studies, have been used for this goal. As a result, several genes were pinned with concurrent and conflicting data among studies. It is important to understand the evolution of techniques and their findings. Conclusions: This review provides a chronological understanding of the different techniques used from the dawn of migraine genetic investigations and the genes linked with the migraine subtypes.

Unravelling the Genetic Landscape of Hemiplegic Migraine: Exploring Innovative Strategies and Emerging Approaches

Migraine is a severe, debilitating neurovascular disorder. Hemiplegic migraine (HM) is a rare and debilitating neurological condition with a strong genetic basis. Sequencing technologies have improved the diagnosis and our understanding of the molecular pathophysiology of HM. Linkage analysis and sequencing studies in HM families have identified pathogenic variants in ion channels and related genes, including CACNA1A, ATP1A2, and SCN1A, that cause HM. However, approximately 75% of HM patients are negative for these mutations, indicating there are other genes involved in disease causation. In this review, we explored our current understanding of the genetics of HM. The evidence presented herein summarises the current knowledge of the genetics of HM, which can be expanded further to explain the remaining heritability of this debilitating condition. Innovative bioinformatics and computational strategies to cover the entire genetic spectrum of HM are also discussed in this review.

Voltage-gated sodium channels in genetic epilepsy: up and down of excitability

The past two decades have witnessed a wide range of studies investigating genetic variants of voltage-gated sodium (NaV ) channels, which are involved in a broad spectrum of diseases, including several types of epilepsy. We have reviewed here phenotypes and pathological mechanisms of genetic epilepsies caused by variants in NaV α and β subunits, as well as of some relevant interacting proteins (FGF12/FHF1, PRRT2, and Ankyrin-G). Notably, variants of all these genes can induce either gain- or loss-of-function of NaV leading to either neuronal hyperexcitability or hypoexcitability. We present the results of functional studies obtained with different experimental models, highlighting that they should be interpreted considering the features of the experimental system used. These systems are models, but they have allowed us to better understand pathophysiological issues, ameliorate diagnostics, orientate genetic counseling, and select/develop therapies within a precision medicine framework. These studies have also allowed us to gain insights into the physiological roles of different NaV channels and of the cells that express them. Overall, our review shows the progress that has been made, but also the need for further studies on aspects that have not yet been clarified. Finally, we conclude by highlighting some significant themes of general interest that can be gleaned from the results of the work of the last two decades.

Migraine: Advances in the Pathogenesis and Treatment

This article presents a comprehensive review on migraine, a prevalent neurological disorder characterized by chronic headaches, by focusing on their pathogenesis and treatment advances. By examining molecular markers and leveraging imaging techniques, the research identifies key mechanisms and triggers in migraine pathology, thereby improving our understanding of its pathophysiology. Special emphasis is given to the role of calcitonin gene-related peptide (CGRP) in migraine development. CGRP not only contributes to symptoms but also represents a promising therapeutic target, with inhibitors showing effectiveness in migraine management. The article further explores traditional medical treatments, scrutinizing the mechanisms, benefits, and limitations of commonly prescribed medications. This provides a segue into an analysis of emerging therapeutic strategies and their potential to enhance migraine management. Finally, the paper delves into neuromodulation as an innovative treatment modality. Clinical studies indicating its effectiveness in migraine management are reviewed, and the advantages and limitations of this technique are discussed. In summary, the article aims to enhance the understanding of migraine pathogenesis and present novel therapeutic possibilities that could revolutionize patient care.

Missense mutations in the membrane domain of PRRT2 affect its interaction with Nav1.2 voltage-gated sodium channels

PRRT2 is a neuronal protein that controls neuronal excitability and network stability by modulating voltage-gated Na⁺ channel (Nav). PRRT2 pathogenic variants cause pleiotropic syndromes including epilepsy, paroxysmal kinesigenic dyskinesia and episodic ataxia attributable to loss-of-function pathogenetic mechanism. Based on the evidence that the transmembrane domain of PRRT2 interacts with Nav1.2/1.6, we focused on eight missense mutations located within the domain that show expression and membrane localization similar to the wild-type protein. Molecular dynamics simulations showed that the mutants do not alter the structural stability of the PRRT2 membrane domain and preserve its conformation. Using affinity assays, we found that the A320V and V286M mutants displayed respectively decreased and increased binding to Nav1.2. Accordingly, surface biotinylation showed an increased Nav1.2 surface exposure induced by the A320V mutant. Electrophysiological analysis confirmed the lack of modulation of Nav1.2 biophysical properties by the A320V mutant with a loss-of-function phenotype, while the V286M mutant displayed a gain-of-function with respect to wild-type PRRT2 with a more pronounced left-shift of the inactivation kinetics and delayed recovery from inactivation. The data confirm the key role played by the PRRT2-Nav interaction in the pathogenesis of the PRRT2-linked disorders and suggest an involvement of the A320 and V286 residues in the interaction site. Given the similar clinical phenotype caused by the two mutations, we speculate that circuit instability and paroxysmal manifestations may arise when PRRT2 function is outside the physiological range.

Genetics of migraine: where are we now?

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes code for proteins expressed in neurons, glial cells, or vessels, all of which increase susceptibility to cortical spreading depression. The study of monogenic migraines has shown that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified numerous susceptibility variants that each result in only a small increase in overall migraine risk. The more than 180 known variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also highlighted the importance of shared genetic factors between migraine and its major co-morbidities, including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes.

Hemiplegic Migraine Associated With PRRT2 Mutations: A Clinical and Genetic Study

BACKGROUND AND OBJECTIVE

PRRT2 variants have been reported in a few cases of patients with hemiplegic migraine. To clarify the role of PRRT2 in familial hemiplegic migraine, we studied this gene in a large cohort of affected probands.

METHODS

PRRT2 was analyzed in 860 probands with hemiplegic migraine and PRRT2 mutations were identified in 30 probands. Genotyping of relatives identified a total of 49 persons with mutations whose clinical manifestations were detailed.

RESULTS

PRRT2 mutations were found in 12 of 163 probands previously tested negative for CACNA1A, ATP1A2 and SCN1A mutations, and in 18 of 697 consecutive probands screened simultaneously on the four genes. In this second group, pathogenic variants were found in 105 subjects, mostly in ATP1A2 (42%), followed by CACNA1A (26%), PRRT2 (17%) and SCN1A (15%). The PRRT2 mutations included seven distinct variants, five of which already described in persons with paroxysmal kinesigenic dyskinesia, and two new variants. Eight probands had a deletion of the whole PRRT2 gene.Among the 49 PRRT2 mutated patients, 26 had pure hemiplegic migraine, 16 had hemiplegic migraine associated with another manifestation: epilepsy (8), learning disabilities (5), hypersomnia (4) or abnormal movement (3). Three patients had epilepsy without migraine, two had paroxysmal kinesigenic dyskinesia without migraine, and one was asymptomatic.

CONCLUSION

PRRT2 should be regarded as the fourth autosomal dominant gene for hemiplegic migraine, and screened in any affected patient, together with the three other main genes. Further studies are needed to understand how the same loss of function PRRT2 mutations can lead to a wide range of neurologic phenotypes including paroxysmal movement disorder, epilepsy, learning disabilities, sleep disorder and hemiplegic migraine.

Relationships between migraine and epilepsy: Pathophysiological mechanisms and clinical implications

Migraine and epilepsy are distinct neurological diseases with specific clinical features and underlying pathophysiological mechanisms. However, numerous studies have highlighted the complex and multifaceted relationships between the two conditions. The relationships between headache and epilepsy manifest themselves in different ways. Firstly, the clinical diagnosis of these disorders may be challenging in view of possible overlapping. While post-ictal headache is a frequent condition, ictal epileptic headache is a rare but challenging diagnosis. Both situations raise the question of the pathophysiological mechanism of headache triggered by seizures. Migraine aura and epilepsy can also exhibit overlapping symptoms leading to their misdiagnosis, in particular in the case of visual aura. Secondly, migraine with aura and epilepsy can occur as a co-morbid condition, particularly in familial hemiplegic migraine (FHM). From a pathophysiological perspective, the identification of genetic mutations in FHM has brought significant advances in the understanding of dysfunctions of neuronal networks leading to hyperexcitability. The purpose of this review is to present clinical situations encompassing headache and epilepsy that can be challenging in neurological practice and to discuss the underlying pathophysiological mechanism of such interactions.

Genetics of migraine

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes encode proteins expressed in neurons, astrocytes or vessels, which all increase the susceptibility to cortical spreading depression. Study of monogenic migraines showed that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified multiple susceptibility variants that only cause a small increase of the global migraine risk. The variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also underscored the importance of genetic factors shared between migraine and its major co-morbidities including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes. Thanks to the advent of new technologies such as induced pluripotent stem cells, genetic data will hopefully finally be able to lead to therapeutic progress.

PRRT2 Related Epilepsies: A Gene Review

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

Exploring the Hereditary Nature of Migraine

Migraine is a common neurological disorder which affects 15-20% of the population; it has a high socioeconomic impact through treatment and loss of productivity. Current forms of diagnosis are primarily clinical and can be difficult owing to comorbidity and symptom overlap with other neurological disorders. As such, there is a need for better diagnostic tools in the form of genetic testing. Migraine is a complex disorder, encompassing various subtypes, and has a large genetic component. Genetic studies conducted on rare monogenic subtypes, including familial hemiplegic migraine, have led to insights into its pathogenesis via identification of causal mutations in three genes (CACNA1A, ATP1A2 and SCN1A) that are involved in transport of ions at synapses and glutamatergic transmission. Study of familial migraine with aura pedigrees has also revealed other causal genes for monogenic forms of migraine. With respect to the more common polygenic form of migraine, large genome-wide association studies have increased our understanding of the genes, pathways and mechanisms involved in susceptibility, which are largely involved in neuronal and vascular functions. Given the preponderance of female migraineurs (3:1), there is evidence to suggest that hormonal or X-linked components can also contribute to migraine, and the role of genetic variants in mitochondrial DNA in migraine has been another avenue of exploration. Epigenetic studies of migraine have shown links between hormonal variation and alterations in DNA methylation and gene expression. While there is an abundance of preliminary studies identifying many potentially causative migraine genes and pathways, more comprehensive genomic and functional analysis to better understand mechanisms may aid in better diagnostic and treatment outcomes.

Episodic Ataxias: Faux or Real?

The term Episodic Ataxias (EA) was originally used for a few autosomal dominant diseases, characterized by attacks of cerebellar dysfunction of variable duration and frequency, often accompanied by other ictal and interictal signs. The original group subsequently grew to include other very rare EAs, frequently reported in single families, for some of which no responsible gene was found. The clinical spectrum of these diseases has been enormously amplified over time. In addition, episodes of ataxia have been described as phenotypic variants in the context of several different disorders. The whole group is somewhat confused, since a strong evidence linking the mutation to a given phenotype has not always been established. In this review we will collect and examine all instances of ataxia episodes reported so far, emphasizing those for which the pathophysiology and the clinical spectrum is best defined.

Familial Hemiplegic Migraine with an ATP1A4 Mutation: Clinical Spectrum and Carbamazepine Efficacy

An Italian family with familial hemiplegic migraine (FHM) with the absence of mutations in the known genes associated with this disorder, namely ATP1A2, ATP1A3, CACNA1A, and SCN1A, has recently been reported. Soon afterward, whole exome sequencing allowed the identification of the carrier status of a heterozygous ATP1A4 mutation c.1798 C >T, in four affected members of this family. Here we compare the clinical symptoms of the affected family members with those from the other FHM families linked to mutations in the known genes associated with this disorder. A further two-year follow-up, including clinical response to carbamazepine administered to the proband and the maternal grandmother due to a worsening of the migraine symptoms, is reported. The clinical condition of the proband’s brother, carrying the same mutation and suffering from congenital ventricular and supraventricular extrasystoles, isdiscussed as well.

The fifth cranial nerve in headaches

The fifth cranial nerve is the common denominator for many headaches and facial pain pathologies currently known. Projecting from the trigeminal ganglion, in a bipolar manner, it connects to the brainstem and supplies various parts of the head and face with sensory innervation. In this review, we describe the neuroanatomical structures and pathways implicated in the sensation of the trigeminal system. Furthermore, we present the current understanding of several primary headaches, painful neuropathies and their pharmacological treatments. We hope that this overview can elucidate the complex field of headache pathologies, and their link to the trigeminal nerve, to a broader field of young scientists.