For Familial Hemiplegic Migraine Research Articles

SCN1A/NaV 1.1 channelopathies: Mechanisms in expression systems, animal models, and human iPSC models.

Pathogenic SCN1A/NaV 1.1 mutations cause well-defined epilepsies, including genetic epilepsy with febrile seizures plus (GEFS+) and the severe epileptic encephalopathy Dravet syndrome. In addition, they cause a severe form of migraine with aura, familial hemiplegic migraine. Moreover, SCN1A/NaV 1.1 variants have been inferred as risk factors in other types of epilepsy. We review here the advancements obtained studying pathologic mechanisms of SCN1A/NaV 1.1 mutations with experimental systems. We present results gained with in vitro expression systems, gene-targeted animal models, and the induced pluripotent stem cell (iPSC) technology, highlighting advantages, limits, and pitfalls for each of these systems. Overall, the results obtained in the last two decades confirm that the initial pathologic mechanism of epileptogenic SCN1A/NaV 1.1 mutations is loss-of-function of NaV 1.1 leading to hypoexcitability of at least some types of γ-aminobutyric acid (GABA)ergic neurons (including cortical and hippocampal parvalbumin-positive and somatostatin-positive ones). Conversely, more limited results point to NaV 1.1 gain-of-function for familial hemiplegic migraine (FHM) mutations. Behind these relatively simple pathologic mechanisms, an unexpected complexity has been observed, in part generated by technical issues in experimental studies and in part related to intrinsically complex pathophysiologic responses and remodeling, which yet remain to be fully disentangled.

Monozygotic twin sisters discordant for familial hemiplegic migraine

BackgroundThe high concordance rate of migraine in monozygotic twin pairs has long been recognised. In the current study, we present a monozygotic twin pair discordant for familial hemiplegic migraine (FHM).Case presentationsWe evaluated 12 adult family members in 2012. The twin pair was separately examined by neurologists at different time points. Mutation screening was performed for known FHM-related genes. The monozygosity of the twins was verified. Eleven individuals had a history of migraine or paroxysmal neurological symptoms, including four patients with motor aura. No mutations were detected in the CACNA1A, ATP1A2, SCN1A, PRRT2 or NOTCH3 genes. The monozygotic twin sisters, aged 52, were discordant for age of onset, motor aura and neuropsychological aura (forced thinking). Overall, the family members presented a wide range of phenotypical features.ConclusionsFamilial hemiplegic migraine is a monogenic disorder that is distinct from migraine with typical aura. However, in certain families with motor aura, such as this one, it is possible that the most severe phenotype is caused by an unlikely combination of polygenic traits and non-genetic factors. In these kindreds, we propose that hemiplegic aura is only a severe and complex form of typical aura.

Newly characterised 5′ and 3′ regions of CACNA1A gene harbour mutations associated with Familial Hemiplegic Migraine and Episodic Ataxia

The CACNA1A gene codes for the α 1A pore-forming subunit of Ca 2+ voltage-gated Cav2.1 channels. CACNA1A mutations are responsible for Familial Hemiplegic Migraine (FHM) type 1, Episodic Ataxia (EA) type 2 and Spinocerebellar Ataxia type 6. The structure of the human gene includes, at present, 49 exons; however almost nothing is known about the 5′ regulatory region, and there is now evidence suggesting the presence of additional exons at the 3′ of the gene. The 892 bp fragment upstream of exon 1 and its deletion mutants were characterised for their transcriptional activity by using luciferase as a reporter gene. The 3′ region was analysed by Rapid Amplification of the cDNA 3′ End. Both regions were screened for mutations in a series of FHM and EA patients by SSCP and sequencing. At the 5′ end of the gene a minimal promoter region was identified within the first 497 bp from ATG. By screening a larger fragment for mutations, the 5 bp deletion (g.-757_-753delCTTTC) was identified in a FHM patient. The deletion significantly increased the transcriptional activity, most likely due to the removal of half a turn of the DNA helix, changing the orientation of downstream binding sites for transcriptional factors. At the 3′ end of the gene a new exon 48, followed by a strong poly-A signal, was identified as well as a new splice variant. The 5 bp insertion (g.38429_38430insCTTTT) in this exon was found in an EA patient. The two new regions can open the way for the study of human CACNA1A gene expression regulation and can be sites of mutations associated with FHM or EA phenotypes.

Migraine: a genetic disease?

Migraines carry a substantial genetic liability, and in families affected with the typical migraines (migraine with, MA, and without aura, MO) linkage to some chromosomal loci has been reported. As yet however, no genes are known for MA/MO, while the three genes discovered as responsible for familial hemiplegic migraine (FHM) are not involved in the typical migraines. Accordingly, we propose to consider FHM as a syndromic migraine and not as a variety of MA. Moreover, we suggest that epigenetic mechanisms play a role in the determination of the typical migraines, and that the primary headaches represent behavioural responses (sickness behaviour, fight-or-flight responses), having adaptive advantage and having been evolutionary conserved, in which pain represents a signal of homeostatic imbalance. Epigenetic mechanisms and this proposed genetic behavioural model could be usefully incorporated into headache genetic research.

Migraine genetics: An update

A growing interest in genetic research in migraine has resulted in the identification of several chromosomal regions that are involved in migraine. However, the identification of mutations in the genes for familial hemiplegic migraine (FHM) forms the only true molecular genetic knowledge of migraine thus far. The increased number of mutations in the FHM1 (CACNA1A) and the FHM2 (ATP1A2) genes allow studying the relationship between genetic findings in both genes and the clinical features in patients. A wide spectrum of symptoms is seen in patients. Additional cerebellar ataxia and (childhood) epilepsy can occur in FHM1 and FHM2. Functional studies show a dysfunction in ion transport as the key factor in the pathophysiology of (familial hemiplegic) migraine that predict an increased susceptibility to cortical spreading depression--the underlying mechanism of migraine aura.

The physiopathology of migraine: the contribution of genetics

Recent advances in the studies of the genetic liability to migraine include the discovery of two genes responsible for familial hemiplegic migraine (FHM) and the analysis of several sites of linkage or genetic association for the so-called typical migraines, e. g., migraine with (MA) and without aura (MO). The 2 genes implicated in the genetics of FHM are CACNA1A for FHM1 and ATP1A2 for FHM2. It is still unclear how dysfunction in these genes may trigger attacks of migraine with hemiplegic features and, in at least part of the families with FHM, also paroxysmal or progressive ataxia and epileptic seizures. It appears that mutations in CACNA1A responsible for FHM1 alter calcium influx and calcium currents in neurons, possible factors of spreading depression like events. On the other hand, abnormal regulation of intracellular calcium concentrations could alter neurotransmitter release and other cellular functions. In the case of ATP1A2 mutations, haplo-insufficiency of the gene has been hypothesised to result in abnormal potassium level regulation because of faulty Na/K exchange with subsequent depolarisation and increased liability to spreading depression, or/and in abnormal calcium levels because of the concomitant activation of the Na/Ca exchanger, with a mechanism therefore comparable to that at work in FHM1. Much more work is clearly necessary to elucidate these pathophysiological mechanisms; advances in genetics however may represent important steps in the clarification of the physiopathology of the migraine attack.

Phenotypes of spinocerebellar ataxia type 6 and familial hemiplegic migraine caused by a unique CACNA1A missense mutation in patients from a large family.

Different mutations in the alpha 1A-subunit of the brain P/Q-type calcium channel gene (CACNA1A) are responsible for familial hemiplegic migraine (FHM), episodic ataxia type 2, and spinocerebellar ataxia type 6 (SCA6). Missense and splice site mutations have been found in FHM and episodic ataxia type 2, respectively, whereas a CAG repeat in the CACNA1A gene was found expanded in patients with SCA6. To identify the disease causing mutation in a large family of patients with phenotypes of hemiplegic migraine with or without cerebellar signs or permanent cerebellar ataxia without migraine inherited in a dominant manner. We examined 15 patients from a large family identified through a systematic survey of hereditary ataxias being conducted in Portugal. Linkage analysis was performed with CACNA1A gene markers, and mutation analysis was performed by single strand conformational polymorphism analysis and sequencing. Genetic linkage analysis with CACNA1A intragenic markers showed positive LOD scores. The maximal LOD score was obtained with the polymorphic CAG repeat (Zmax = 4.47, theta = 0). By single-strand conformational polymorphism analysis, a shift in exon 13 of the CACNA1A gene was detected in all patients. A G-to-A substitution was then identified, resulting in an arginine-to-glutamine change at codon 583 of this calcium channel alpha 1A-subunit. The disease-causing mutation in this family was identified, showing that a unique mutation in the CACNA1A gene causes several phenotypes, including those of SCA6 and FHM, thus suggesting that SCA6 and FHM are not only allelic diseases but are the same disorder with a large phenotypic variability.

Physical mapping and characterization of the human Na,K-ATPase isoform, ATP1A4

Four isoforms of the catalytic α subunit of the Na,K-ATPase have been previously identified. We characterized and mapped a genomic copy of the human ATP1A4 isoform between D1S2707 and WI-9524, telomeric to a nearby isoform ATP1A2, and within a candidate region at 1q23 for familial hemiplegic migraine (FHM). Human ATP1A4 gene shares 84% identity with the mouse Atp1a4 gene, and both consist of 22 exons and 21 introns. The predicted polypeptide is 1029 amino acids and shares 82 and 79.8% identity, respectively, with human ATP1A2 and ATP1A1. ATP1A4 is larger than other isoforms and most divergent at the N-terminus. ATP1A4 and ATP1A2 are paralogous genes with the same number and organization of putative H-transmembrane domains, conserved exon–intron boundaries, and are found approximately 8.5 kb apart. Expression analysis of the ATP1A4 gene revealed a new major ∼7.5 kb transcript in human skeletal muscle, with expression also shown in mouse muscle. Predictive analysis of promoter regions identified muscle specific regulatory elements for ATP1A4 and Atp1a4. Mutation analysis among eight affected individuals from a single large, highly penetrant FHM family was negative in ATP1A4 and ATP1A2 although multiple polymorphisms were identified.

The inheritance of migraine with aura estimated by means of structural equation modelling

Studies of migraine with aura (MA) have shown familial aggregation of the disorder, which cannot be explained by simple mendelian inheritance. The interest in a genetic basis for the disorder...

Episodic ataxia type 2 (EA2) and spinocerebellar ataxia type 6 (SCA6) due to CAG repeat expansion in the CACNA1A gene on chromosome 19p.

Point mutations of the CACNA1A gene coding for the alpha 1A voltage-dependent calcium channel subunit are responsible for familial hemiplegic migraine (FHM) and episodic ataxia type 2 (EA2). In addition, expansions of the CAG repeat motif at the 3' end of the gene, smaller than those responsible for dynamic mutation disorders, were found in patients with a progressive spinocerebellar ataxia, named SCA6. In the present work, the analysis of two new families with small CAG expansions of the CACNA1A gene is presented. In one family, with a clinical diagnosis of EA2, a CAG23 repeat allele segregated in patients showing different interictal symptoms, ranging from nystagmus only to severe progressive cerebellar ataxia. No additional mutations in coding and intron-exon junction sequences in disequilibrium with the CAG expansion were found. In the second family, initially classified as autosomal dominant cerebellar ataxia of unknown type, an inter-generational allele size change showed that a CAG20 allele was associated with an EA2 phenotype and a CAG25 allele with progressive cerebellar ataxia. These results show that EA2 and SCA6 are the same disorder with a high phenotypic variability, at least partly related to the number of repeats, and suggest that the small expansions may not be as stable as previously reported. A refinement of the coding and intron-exon junction sequences of the CACNA1A gene is also provided.

Familial Hemiplegic Migraine and Episodic Ataxia Type-2 Are Caused by Mutations in the Ca 2+ Channel Gene CACNL1A4

Genes for familial hemiplegic migraine (FHM) and episodic ataxia type-2 (EA-2) have been mapped to chromosome 19p13. We characterized a brain-specific P/Q-type Ca 2+ channel α1-subunit gene, CACNL1A4, covering 300 kb with 47 exons. Sequencing of all exons and their surroundings revealed polymorphic variations, including a (CA) n-repeat (D19S1150), a (CAG) n-repeat in the 3′-UTR, and different types of deleterious mutations in FHM and EA-2. In FHM, we found four different missense mutations in conserved functional domains. One mutation has occurred on two different haplotypes in unrelated FHM families. In EA-2, we found two mutations disrupting the reading frame. Thus, FHM and EA-2 can be considered as allelic channelopathies. A similar etiology may be involved in common types of migraine.