Increased risk of migraine with typical aura in probands with familial hemiplegic migraine and their relatives

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.

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.

Pathophysiology of migraine aura

Migraine aura occurs in about a third of patients with migraine and consists of a group of transient focal neurological symptoms that appear from 5 to 60min and then resolve prior to or in the early phase of a migraine headache attack. Migraine auras may consist of visual, language, unilateral sensory, or motor symptoms. There has been considerable debate as to the origins of the migrainous aura. Investigations during physiologically induced visual auras suggest that the phenomenon of cortical spreading depression or its human equivalent underpins the migraine aura. Single gene defects have been linked to relatively rare forms of the motor subtypes of aura known as familial hemiplegic migraine (FHM). These include CACNA1A (FHM1), ATP1A2 (FHM2), and SCN1A (FHM3). In the familial hemiplegic forms of migraine, the more typical forms of aura are almost always also present. Despite ample epidemiological evidence of increased heritability of migraine with aura compared to migraine without aura, identification of the specific variants driving susceptibility to the more common forms of aura has been problematic thus far. In the first genome-wide association study (GWAS) that focused migraine with aura, a single SNP rs835740 reached genome-wide significance. Unfortunately, the SNP did show statistical significance in a later meta-analysis which included GWAS data from subsequent studies. Here, we review the clinical features, pathophysiological theories, and currently available potential evidence for the genetic basis of migraine aura.

Genetics of migraine aura: an update

Migraine is a common brain disorder with a large genetic component. Of the two main migraine types, migraine with aura and migraine without aura, the genetic underpinning in the former is least understood. Given the evidence from epidemiological studies in cohorts and families that the genetic contribution is highest in migraine with aura, this seems paradoxical. Various genetic approaches have been applied to identify genetic factors that confer risk for migraine. Initially, so-called candidate gene associations studies (CGAS) have been performed that test DNA variants in genes prioritized based on presumed a priori knowledge of migraine pathophysiology. More recently, genome-wide association studies (GWAS) tested variants in any gene in an hypothesis-free manner. Whereas GWAS in migraine without aura, or the more general diagnosis migraine have already identified dozens of gene variants, the specific hunt for gene variants in migraine with aura has been disappointing. The only GWAS specifically investigating migraine with aura yielded only one single associated single nucleotide polymorphism (SNP), near MTDH and PGCP, with genome-wide significance. However, interrogation of all genotyped SNPs, so beyond this one significant hit, was more successful and led to the notion that migraine with aura and migraine without aura are genetically more alike than different. Until now, most relevant genetic discoveries related to migraine with aura came from investigating monogenetic syndromes with migraine aura as a prominent phenotype (i.e. FHM, CADASIL and FASPS). This review will highlight the genetic findings relevant to migraine with aura.

White Matter Hyperintensities in Patients with Sporadic Hemiplegic Migraine

BACKGROUND AND PURPOSE

To identify the differences in overall occurrence, location, and disease burden of white matter hyperintensities (WMH) in patients with sporadic hemiplegic migraine (SHM) and patients with migraine headaches.

METHODS

We included patients who met diagnostic criteria proposed by the third International Classification of Headache Disorders (ICHD-3) for SHM and migraine headache. WMHs were identified using T2 fluid-attenuated inversion recovery axial sequence and classified based upon the location. The disease burden was assessed using Scheltens visual rating scale.

RESULTS

Fifty patients met the diagnostic criteria for SHM and 100 patients for migraine headache. Patients in the study group were similar to the control group in terms of age (47.7 ± 12.2 years vs. 48.17 ± 9.7 years; P = .814) and gender (M: F; 14:36 vs. M: F 25:75; P = .693). WMH were found in 28 (56%) patients with SHM and 44 (44%) in patients with migraine headache. The proportion of patients with WMH was not different between the two groups (P = .166). On univariate analysis, the proportion of patients with WMH in parietal, occipital, and infratentorial regions was higher in patients with SHM. White matter burden determined by visual rating scale and proportion of patients with lesions ≥5 mm in diameter was also significantly higher in patients with SHM. On multivariate analysis, the WMH occurrence in the parietal lobe (P = .043) was found to be significantly higher in SHM.

CONCLUSIONS

The WMH occurrence in patients with SHM is significantly more in the parietal lobe when compared to those with migraine headaches. WMH burden was also higher in patients with SHM, and larger white matter lesions occurred more frequently in these patients with SHM (compared to ordinary migraineurs).

Lack of association between urotensin-II (UTS2) gene polymorphisms (Thr21Met and Ser89Asn) and migraine

Migraine is a common neurovascular brain disorder with heterogeneous clinical presentation, including recurrent headache attacks. The pathophysiology of migraine is complex, and a number of genomic regions have been associated with the development of migraine. In this study, we analyzed the allele and genotype frequencies of the urotensin-II gene (UTS2) polymorphisms, Thr21Met and Ser89Asn, among Turkish patients with migraine. A total of 146 patients with migraine (14 with aura [MA group] and 132 without aura [MO group]) were genotyped for Thr21Met and Ser89Asn polymorphisms and compared with 154 age- and sex-matched healthy controls. The UTS2 gene polymorphisms were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). No significant differences were observed in allele and genotype frequencies for Thr21Met and Ser89Asn polymorphisms between the patients with migraine and control group. Similarly, we did not observe significant differences in allele and genotype frequencies between MA and MO and control group. Moreover, the haplotype analysis showed no association between UTS2 gene haplotypes (MN, MS, TN, and TS) and migraine. In summary, Thr21Met and Ser89Asn polymorphisms of the UTS2 gene are not risk factors for migraine in our sample of Turkish migraine patients.

Targeted next generation sequencing identifies novel NOTCH3 gene mutations in CADASIL diagnostics patients

BACKGROUND

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a monogenic, hereditary, small vessel disease of the brain causing stroke and vascular dementia in adults. CADASIL has previously been shown to be caused by varying mutations in the NOTCH3 gene. The disorder is often misdiagnosed due to its significant clinical heterogeneic manifestation with familial hemiplegic migraine and several ataxia disorders as well as the location of the currently identified causative mutations. The aim of this study was to develop a new, comprehensive and efficient single assay strategy for complete molecular diagnosis of NOTCH3 mutations through the use of a custom next-generation sequencing (NGS) panel for improved routine clinical molecular diagnostic testing.

RESULTS

Our custom NGS panel identified nine genetic variants in NOTCH3 (p.D139V, p.C183R, p.R332C, p.Y465C, p.C597W, p.R607H, p.E813E, p.C977G and p.Y1106C). Six mutations were stereotypical CADASIL mutations leading to an odd number of cysteine residues in one of the 34 NOTCH3 gene epidermal growth factor (EGF)-like repeats, including three new typical cysteine mutations identified in exon 11 (p.C597W; c.1791C>G); exon 18 (p.C977G; c.2929T>G) and exon 20 (p.Y1106C; c.3317A>G). Interestingly, a novel missense mutation in the CACNA1A gene was also identified in one CADASIL patient. All variants identified (novel and known) were further investigated using in silico bioinformatic analyses and confirmed through Sanger sequencing.

CONCLUSIONS

NGS provides an improved and effective methodology for the diagnosis of CADASIL. The NGS approach reduced time and cost for comprehensive genetic diagnosis, placing genetic diagnostic testing within reach of more patients.

Prevalence of lifetime depression in a large hemiplegic migraine cohort

OBJECTIVE

To determine the prevalence of depression and determinants associated with depression in a large population of hemiplegic migraine (HM) patients.

METHODS

We conducted a cross-sectional, validated questionnaire study among 89 well-defined HM patients and 235 headache-free controls. The prevalence of lifetime depression and its relation to migraine characteristics was assessed.

RESULTS

HM patients had increased odds for lifetime depression (odds ratio 3.73, 95% confidence interval 2.18-6.38) compared with controls. Use of acute antimigraine medication was associated with lifetime depression.

CONCLUSIONS

Depression is part of the monogenic hemiplegic migraine phenotype. Further studies are needed to elucidate the pathophysiologic role of HM genes in comorbid depression. For now, clinicians should take comorbid depression into consideration when starting prophylactic treatment of HM.

Familial Aggregation of Migraine and Depression: Insights From a Large Australian Twin Sample

OBJECTIVES

This research examined the familial aggregation of migraine, depression, and their co-occurrence.

METHODS

Diagnoses of migraine and depression were determined in a sample of 5,319 Australian twins. Migraine was diagnosed by either self-report, the ID migraine™ Screener, or International Headache Society (IHS) criteria. Depression was defined by fulfilling either major depressive disorder (MDD) or minor depressive disorder (MiDD) based on the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria. The relative risks (RR) for migraine and depression were estimated in co-twins of twin probands reporting migraine or depression to evaluate their familial aggregation and co-occurrence.

RESULTS

An increased RR of both migraine and depression in co-twins of probands with the same trait was observed, with significantly higher estimates within monozygotic (MZ) twin pairs compared to dizygotic (DZ) twin pairs. For cross-trait analysis, the RR for migraine in co-twins of probands reporting depression was 1.36 (95% CI: 1.24-1.48) in MZ pairs and 1.04 (95% CI: 0.95-1.14) in DZ pairs; and the RR for depression in co-twins of probands reporting migraine was 1.26 (95% CI: 1.14-1.38) in MZ pairs and 1.02 (95% CI: 0.94-1.11) in DZ pairs. The RR for strict IHS migraine in co-twins of probands reporting MDD was 2.23 (95% CI: 1.81-2.75) in MZ pairs and 1.55 (95% CI: 1.34-1.79) in DZ pairs; and the RR for MDD in co-twins of probands reporting IHS migraine was 1.35 (95% CI: 1.13-1.62) in MZ pairs and 1.06 (95% CI: 0.93-1.22) in DZ pairs.

CONCLUSIONS

We observed significant evidence for a genetic contribution to familial aggregation of migraine and depression. Our findings suggest a bi-directional association between migraine and depression, with an increased risk for depression in relatives of probands reporting migraine, and vice versa. However, the observed risk for migraine in relatives of probands reporting depression was considerably higher than the reverse. These results add further support to previous studies suggesting that patients with comorbid migraine and depression are genetically more similar to patients with only depression than patients with only migraine.

Recurrent coma and fever in familial hemiplegic migraine type 2. A prospective 15-year follow-up of a large family with a novel ATP1A2 mutation

Background Familial hemiplegic migraine (FHM) is a rare monogenic migraine subtype characterised by attacks associated with transient motor weakness. Clinical information is mainly based on reports of small families with only short follow-up. Here, we document a prospective 15-year follow-up of an extended family with FHM type 2. Patients and methods After diagnosing FHM in a patient with severe attacks associated with coma and fever, we identified eight more family members with FHM and one with possible FHM. All family members were prospectively followed for 15 years. In total 13 clinically affected and 21 clinically non-affected family members were genetically tested and repeatedly investigated. Results A novel p.Arg348Pro ATP1A2 mutation was found in 14 family members: 12 with clinical FHM, one with psychomotor retardation and possible FHM, and one without FHM features. In 9/12 (75%) family members with genetically confirmed FHM, attacks were severe, long-lasting, and often associated with impaired consciousness and fever. Such attacks were frequently misdiagnosed and treated as viral meningitis or stroke. Epilepsy was reported in three family members with FHM and in the one with psychomotor retardation and possible FHM. Ataxia was not observed. Conclusion FHM should be considered in patients with recurrent coma and fever.

Monozygotic twin sisters discordant for familial hemiplegic migraine

BACKGROUND

The 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 PRESENTATIONS

We 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.

CONCLUSIONS

Familial 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.

Familial and sporadic hemiplegic migraine: diagnosis and treatment

OPINION STATEMENT

Hemiplegic migraine (HM) is a rare subtype of migraine with aura, characterized by transient hemiparesis during attacks. Diagnosis is based on the International Classification of Headache Disorders criteria (ICHD-II). Two types of HM are recognized: familial (FHM) and sporadic hemiplegic migraine (SHM). HM is genetically heterogeneous. Three genes have been identified (CACNA1A, ATP1A2, and SCN1A) but more, so far unknown genes, are involved. Clinically, attacks of the 3 subtypes cannot be distinguished. The diagnosis can be confirmed but not ruled out by genetic testing, because in some HM patients other, not yet identified, genes are involved. The presence of additional symptoms (such as chronic ataxia or epilepsy) may increase the likelihood of identifying a mutation. Additional diagnostics like imaging, CSF analysis, or an EEG are mainly performed to exclude other causes of focal neurological symptoms associated with headache. Conventional cerebral angiography is contraindicated in HM because this may provoke an attack. Because HM is a rare condition, no clinical treatment trials are available in this specific subgroup of migraine patients. Thus, the treatment of HM is based on empirical data, personal experience of the treating neurologist, and involves a trial-and-error strategy. Acetaminophen and NSAIDs often are the first choice in acute treatment. Although controversial in HM, triptans can be prescribed when headaches are not relieved sufficiently with common analgesics. An effective treatment for the severe and often prolonged aura symptoms is more warranted, but currently no such acute treatment is available. Prophylactic treatment can be considered when attack frequency exceeds 2 attacks per month, or when severe attacks pose a great burden that requires reduction of severity and frequency. In no strictly preferred order, flunarizine, sodium valproate, lamotrigine, verapamil, and acetazolamide can be tried. While less evidence is available for prophylactic treatment with topiramate, candesartan, and pizotifen, these drugs can also be considered. The use of propranolol in HM is more controversial, but evidence of adverse effects is insufficient to contraindicate beta-blockers.

Emerging genomic biomarkers in migraine

Migraine is a debilitating neurovascular condition classified as either migraine with aura or migraine without aura. A significant genetic basis has been implicated in migraine and has probed the role of neurotransmitters, hormones and vascular genes in this disorder. The aim of this review is to highlight the recent genetic discoveries contributing to our understanding of the complex pathogenesis of migraine. The current review will discuss the role of neurotransmitter-related genes in migraine, including the recently identified TRESK and variants of the KCNN3 gene, as well as outlining studies investigating hormone receptor genes, such as ESR1 and PGR, and vascular-related genes, including the MTHFR and NOTCH 3 genes.

Migraine and behavior in children: influence of maternal headache frequency

We took advantage of a large population study in order to measure child behavior, as captured by the Child Behavior Checklist (CBCL) as a function of headache status in the children and their mothers. Of the target sample, consents and analyzable data were obtained from 1,856 families (85.4 %). Headache diagnoses were defined according to the second edition of the International Classification of Headache Disorders, and behavioral and emotional symptoms were assessed by the validated Brazilian version of the CBCL. We calculated the relative risk of abnormalities in the CBCL domains as a function of headache status in the children, after adjusting by a series of main effect models. Children with migraine were more likely to present abnormal scores in several of the CBCL scales, relative to children without migraine, and maternal migraine status contributed little to the model. However, when the mother had daily headaches, both children with and without migraine had similar CBCL scores. In multivariate analyses, migraine status in the children predicted CBCL scores (p < 0.01). Headache status and headache frequency in the mother did not predict CBCL scores in children with migraine but predicted in children without migraine (p < 0.01). The burden of migraine to the family is complex. Children with migraine are more likely to have behavioral and emotional symptoms than children without migraine. Children without migraine may be affected, in turn, by frequent headaches experienced by their mothers.

Neuronal P/Q-type calcium channel dysfunction in inherited disorders of the CNS

The past two decades have witnessed the emergence of a new and expanding field of neurological diseases--the genetic ion channelopathies. These disorders arise from mutations in genes that encode ion channel subunits, and manifest as paroxysmal attacks involving the brain or spinal cord, and/or muscle. The voltage-gated P/Q-type calcium channel (P/Q channel) is highly expressed in the cerebellum, hippocampus and cortex of the mammalian brain. The P/Q channel has a fundamental role in mediating fast synaptic transmission at central and peripheral nerve terminals. Autosomal dominant mutations in the CACNA1A gene, which encodes voltage-gated P/Q-type calcium channel subunit α(1) (the principal pore-forming subunit of the P/Q channel) are associated with episodic and progressive forms of cerebellar ataxia, familial hemiplegic migraine, vertigo and epilepsy. This Review considers, from both a clinical and genetic perspective, the various neurological phenotypes arising from inherited P/Q channel dysfunction, with a focus on recent advances in the understanding of the pathogenetic mechanisms underlying these disorders.

A long-term follow-up study of 18 patients with sporadic hemiplegic migraine

Objective: Our objective was to study the long-term prognosis of sporadic hemiplegic migraine (SHM).

Methods: We performed a longitudinal follow-up study in 18 patients who were diagnosed with SHM between 1993 and 1996. Follow-up time between the first and second survey ranged from nine to 14 years. These patients were included as part of a genetic study in which we systematically analysed the role of the three known familial hemiplegic migraine (FHM) genes.

Results: In 12 out of 18 patients the clinical diagnosis was unchanged. In two of the six remaining patients the attacks were no longer associated with hemiplegia; one of them had an ATP1A2 gene mutation (E120A). In the four other patients, the diagnosis changed into FHM, because a family member had developed hemiplegic migraine since the initial diagnosis was made. In two of the four patients a mutation was demonstrated ( CACNA1A [R583Q] and ATP1A2 [R834X]).

Conclusion: This study shows that the diagnosis of SHM changes into FHM in a considerable percentage of patients (22% [4 of 18]), almost a decade after the initial diagnosis. This indicates that a careful follow-up of SHM patients and their families is advisable for optimal care and counseling. Diagnostic screening of FHM genes in SHM patients can be of value. Our genetic and clinical follow-up studies reinforce the evidence that FHM and SHM are part of the same spectrum of migraine.

Insights into migraine mechanisms and CaV2.1 calcium channel function from mouse models of familial hemiplegic migraine

Migraine is a very common disabling brain disorder with unclear pathogenesis. A subtype of migraine with aura (familial hemiplegic migraine type 1: FHM1) is caused by mutations in CaV2.1 (P/Q-type) Ca2+ channels. This review describes the functional consequences of FHM1 mutations in knockin mouse models carrying the mild R192Q or severe S218L mutations in the orthologous gene. The FHM1 knockin mice show allele dosage-dependent gain-of-function of neuronal P/Q-type Ca2+ current, reflecting activation of mutant channels at lower voltages, and allele dosage- and sex-dependent facilitation of induction and propagation of cortical spreading depression (CSD), the phenomenon that underlies migraine aura. Gain-of-function of neuronal Ca2+ current, facilitation of CSD and post-CSD motor deficits were larger in S218L than R192Q knockin mice, in correlation with the more severe human S218L phenotype. Enhanced cortical excitatory neurotransmission, due to increased action potential-evoked Ca2+ influx and increased probability of glutamate release at pyramidal cell synapses, but unaltered inhibitory neurotransmission at fast-spiking interneuron synapses, were demonstrated in R192Q knockin mice. Evidence for a causative link between enhanced glutamate release and CSD facilitation was obtained. The data from FHM1 mice strengthen the view of CSD as a key player in the pathogenesis of migraine, give insight into CSD mechanisms and point to episodic disruption of excitation-inhibition balance and neuronal hyperactivity as the basis for vulnerability to CSD ignition in migraine.

Enhanced excitatory transmission at cortical synapses as the basis for facilitated spreading depression in Ca(v)2.1 knockin migraine mice

Migraine is a common disabling brain disorder. A subtype of migraine with aura (familial hemiplegic migraine type 1: FHM1) is caused by mutations in Ca(V)2.1 (P/Q-type) Ca(2+) channels. Knockin mice carrying a FHM1 mutation show increased neuronal P/Q-type current and facilitation of induction and propagation of cortical spreading depression (CSD), the phenomenon that underlies migraine aura and may activate migraine headache mechanisms. We studied cortical neurotransmission in neuronal microcultures and brain slices of FHM1 mice. We show gain of function of excitatory neurotransmission due to increased action-potential-evoked Ca(2+) influx and increased probability of glutamate release at pyramidal cell synapses but unaltered inhibitory neurotransmission at fast-spiking interneuron synapses. Using an in vitro model of CSD, we show a causative link between enhanced glutamate release and CSD facilitation. The synapse-specific effect of FHM1 mutations points to disruption of excitation-inhibition balance and neuronal hyperactivity as the basis for episodic vulnerability to CSD ignition in migraine.

Divergent sodium channel defects in familial hemiplegic migraine

Familial hemiplegic migraine type 3 (FHM3) is a severe autosomal dominant migraine disorder caused by mutations in the voltage-gated sodium channel Na(V)1.1 encoded by SCN1A. We determined the functional consequences of three mutations linked to FHM3 (L263V, Q1489K, and L1649Q) in an effort to identify molecular defects that underlie this inherited migraine disorder. Only L263V and Q1489K generated quantifiable sodium currents when coexpressed in tsA201 cells with the human beta(1) and beta(2) accessory subunits. The third mutant, L1649Q, failed to generate measurable whole-cell current because of markedly reduced cell surface expression. Compared to WT-Na(V)1.1, Q1489K exhibited increased persistent current but also enhanced entry into slow inactivation as well as delayed recovery from fast and slow inactivation, thus resulting in a predominantly loss-of-function phenotype further demonstrated by a greater loss of channel availability during repetitive stimulation. In contrast, L263V exhibited gain-of-function features, including delayed entry into, as well as accelerated recovery from, fast inactivation; depolarizing shifts in the steady-state voltage dependence of fast and slow inactivation; increased persistent current; and delayed entry into slow inactivation. Notably, the two mutations (Q1489K and L1649Q) that exhibited partial or complete loss of function are linked to typical FHM, whereas the gain-of-function mutation L263V occurred in a family having both FHM and a high incidence of generalized epilepsy. We infer from these data that a complex spectrum of Na(V)1.1 defects can cause FHM3. Our results also emphasize the complex relationship between migraine and epilepsy and provide further evidence that both disorders may share common molecular mechanisms.

Familial hemiplegic migraine type 1 shows no hypersensitivity to nitric oxide

Familial hemiplegic migraine type 1 (FHM-1) is a dominantly inherited subtype of migraine with aura and transient hemiplegia associated with mutations in the CACNA1A gene. FHM-1 shares many phenotypical similarities with common types of migraine, indicating common neurobiological pathways. Experimental studies have established that activation of the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway plays a crucial role in migraine pathophysiology. Therefore, we tested the hypothesis that CACNA1A mutations in patients with FHM-1 are associated with hypersensitivity to NO-cGMP pathway. We included eight FHM-1 patients with R583Q and C1369Y mutations and nine healthy controls, who received intravenous infusions of 0.5 microg kg(-1) min(-1) glyceryl trinitrate (GTN) over 20 min. We recorded: headache intensity on a verbal rating scale; mean flow velocity in the middle cerebral artery (V(meanMCA)) by transcranial Doppler; diameter of the superficial temporal artery (STA) by Dermascan. One patient reported migraine without aura 5 h after start of the GTN infusion. No aura was reported. The AUC(headache) in the immediate phase was more pronounced in patients than in controls (P = 0.01). In the 14 h following GTN infusion, there was no difference in the AUC(headache) between patients and controls (P = 0.17). We found no difference in the AUC(VmeanMCA) (P = 0.12) or AUC(STA) (P = 0.71) between FHM-1 patients and controls. None of the control persons reported migraine-like headache. FHM-1 patients do not show hypersensitivity of the NO-cGMP pathway, as characteristically seen in migraine patients with and without aura. This indicates that the pathophysiological pathways underlying migraine headache in FHM-1 may be different from the common types of migraine.

Migraine: gene mutations and functional consequences

PURPOSE OF REVIEW

Genetic and functional studies of mutations in familial hemiplegic migraine reveal a major role for disturbed ion transport. Gene identification in common, multifactorial migraine remains challenging.

RECENT FINDINGS

Several new mutations have been identified in FHM1, FHM2 and FHM3 genes. Functional consequences of familial hemiplegic migraine mutations point to an important role for cortical spreading depression in migraine pathophysiology. New genetic approaches have been tested in common migraine - novel chromosomal loci - but no gene variants have been identified.

SUMMARY

Identification and analysis of gene mutations in familial hemiplegic migraine revealed a major role for disturbed ion transport in this disorder. Cellular and transgenic mouse models of familial hemiplegic migraine genes suggest that increased potassium and glutamate play a role in the pathophysiology of the disorder. Despite progress, no genes have been discovered for common migraine.

Familial hemiplegic migraine

Familial hemiplegic migraine (FHM) is a rare and genetically heterogeneous autosomal dominant subtype of migraine with aura. Mutations in the genes CACNA1A and SCNA1A, encoding the pore-forming alpha(1) subunits of the neuronal voltage-gated Ca2+ channels Ca(V)2.1 and Na+ channels Na(V)1.1, are responsible for FHM1 and FHM3, respectively, whereas mutations in ATP1A2, encoding the alpha2 subunit of the Na+, K+ adenosinetriphosphatase (ATPase), are responsible for FHM2. This review discusses the functional studies of two FHM1 knockin mice and of several FHM mutants in heterologous expression systems (12 FHM1, 8 FHM2, and 1 FHM3). These studies show the following: (1) FHM1 mutations produce gain-of-function of the Ca(V)2.1 channel and, as a consequence, increased Ca(V)2.1-dependent neurotransmitter release from cortical neurons and facilitation of in vivo induction and propagation of cortical spreading depression (CSD: the phenomenon underlying migraine aura); (2) FHM2 mutations produce loss-of-function of the alpha2 Na+,K+-ATPase; and (3) the FHM3 mutation accelerates recovery from fast inactivation of Na(V)1.5 (and presumably Na(V)1.1) channels. These findings are consistent with the hypothesis that FHM mutations share the ability of rendering the brain more susceptible to CSD by causing either excessive synaptic glutamate release (FHM1) or decreased removal of K+ and glutamate from the synaptic cleft (FHM2) or excessive extracellular K+ (FHM3). The FHM data support a key role of CSD in migraine pathogenesis and point to cortical hyperexcitability as the basis for vulnerability to CSD and to migraine attacks. Hence, they support novel therapeutic strategies that consider CSD and cortical hyperexcitability as key targets for preventive migraine treatment.

Targeting neuronal hyperexcitability for antimigraine drug development

Migraine is among the most prevalent neurological disorders worldwide, afflicting up to 16% of the population. Because it mostly affects patients between the most productive ages of 25 and 50 years, migraine costs employers more than US$13 billion per year in reduced productivity and missed days. It is therefore important to prevent and treat migraine attacks. Triptans were introduced in the early 1990s and effectively alleviate symptoms in most patients. Their success was based on the existence of the operational hypothesis implicating the trigemino-vascular system. Prophylactic medications have been available since beta-blockers, followed by agents belonging to other therapeutic classes. Most of them were found serendipitously to be effective. However, progress in the development of preventative agents has been hampered by the lack of animal models mimicking the early events of migraine pathophysiology. This review will examine how a recent theory on the origin of migraine attacks is likely to lead to the development of new animal models.

A novel ATP1A2 mutation in a family with FHM type II

Familial hemiplegic migraine (FHM) is a rare subtype of migraine with aura with an autosomal dominant pattern of inheritance. Six FHM families underwent extensive clinical and genetic investigation. The authors identified a novel ATP1A2 mutation (E700K) in three patients from one family. In the patients, attacks were triggered by several factors including minor head trauma. In one subject a 3-day coma developed after a cerebral angiography. Overall, the phenotype of the patients closely resembles that of previously reported cases of FHM type II. The E700K variant might be regarded as the cause of the disease in this family, but this was not tested functionally.

The CACNA1A and ATP1A2 genes are not involved in dominantly inherited migraine with aura

Epidemiological studies indicate that migraine with typical aura (MA) has a major genetic component but the genes for MA have not been identified. However, the autosomal dominantly inherited familial hemiplegic migraine (FHM) is often caused by mutations in the CACNA1A or ATP1A2 genes. The aim of the study was to investigate if the CACNA1A or ATP1A2 genes are involved in MA with an apparently autosomal dominant mode of inheritance. From a clinic population diagnosed by a trained physician we recruited 34 extended families (comprising 174 MA patients) with an apparently autosomal dominant mode of inheritance of MA. We performed a linkage analysis of 161 of 174 MA patients and 79 unaffected relatives using a framework marker set of 44 markers for chromosome 1 and 22 markers for chromosome 19. Linkage analysis was made with a non-parametric or autosomal dominant parametric model, either allowing for heterogeneity or not, using an affected only analysis. We identified no linkage to CACNA1A and ATP1A2 loci on chromosome 19 or 1, respectively. Additionally, at least two patients from each family and 92 healthy, unrelated controls were selected for a sequence analysis. We sequenced the 48 exons of CACNA1A and the 23 exons of ATP1A2, including promoter and flanking intron sequences. No polymorphism was identified in the CACNA1A or ATP1A2 genes with a strong correlation to MA. Our study shows that the CACNA1A or ATP1A2 genes are probably not involved in MA. To identify the genes involved in the common forms of migraine, future genetic studies should focus on MA and migraine without aura (MO) and not FHM.

Familial risks for migraine and other headaches among siblings based on hospitalizations in Sweden

Migraine and other headaches are common disabling conditions, reducing the quality of life in the affected individuals. The unambiguous definition of familial risk for subtypes of migraine and other headaches will advance the search for the heritable causes of these conditions and their underlying mechanisms. We aim at defining familial risks for siblings to be hospitalized because of migraine or other headaches. An ad hoc migraine database was constructed by linking the Multigeneration Register on 0- to 69-year-old siblings to the Hospital Discharge Register for data on migraines of all hospitalized patients in Sweden from years 1987 to 2001. Standardized incidence ratios (SIRs) were calculated for affected sibling pairs by comparison with those whose siblings had no migraine. Among a total of 14,123 hospitalized patients, 205 affected siblings were identified, with a familial SIR of 2.84. SIRs for migraine with and without aura were 3.08 and 2.67, respectively. The highest familial risk of 3.71 was noted for unspecified migraine. The risk tended to be higher for concordant (both siblings sharing the migraine subtype, ranging from 4.0 to 6.0) than discordant subtypes, but even many discordant SIRs were significant. The SIR for spouse correlation was 1.14 for husbands and 1.22 for wives, far from being significant. All subtypes of hospitalized migraines and other headaches show an increased familial risk, at least in specific age groups. The different subtypes appear to share susceptibility, which may imply common disease mechanisms.

Recent findings in headache genetics

PURPOSE OF REVIEW

The progress in headache genetics, especially migraine genetics, recently jumped ahead with some major discoveries.

RECENT FINDINGS

Family and epidemiological studies further strengthen the genetic contribution to migraine and two recent observations gave new molecular insights in the disease. Studies on the genetics of familial hemiplegic migraine revealed, in addition to the previously identified familial hemiplegic migraine type 1 gene CACNA1A on chromosome 19, the familial hemiplegic migraine type 2 gene ATP1A2, encoding the alpha2-subunit of sodium/potassium pumps. Recent genome screens in families with migraine identified susceptibility loci on chromosomes 4, 6, 11 and 14.

SUMMARY

The findings in familial hemiplegic migraine confirm that dysfunction in ion transport is a key factor in migraine pathophysiology and might help us in the elucidation of migraine molecular pathways. The identification of several migraine susceptibility loci underline its genetically complex nature.

Toward a molecular genetic classification of familial hemiplegic migraine

The genetics of migraine is a fascinating and rapidly moving research area. Familial hemiplegic migraine, a rare subtype of migraine with a Mendelian pattern of inheritance, is caused by mutations in the chromosome 19 CACNA1A gene or in the chromosome 1 ATP1A2 gene. Familial migraine variants are classified on the basis of clinical, descriptive criteria, but this is insufficient. In the future, a diagnostic classification based on mutation-analysis is needed.