Genetics of migraine: an update with special attention to genetic comorbidity

Dissecting the association between migraine and stroke

Migraine is a common disabling neurological disorder resulting from excessive cortical excitation and trigeminovascular afferent sensitization. In addition to aberrant neuronal processing, migraineurs are also at significant risk of vascular disease. Consequently, the impact of migraine extends well beyond the ictal headache and includes a well-documented association with acute ischemic stroke, particularly in young women with a history of migraine with aura. The association between migraine and stroke has been acknowledged for 40 years or more. However, examining the pathobiology of this association has become a more recent and critically important undertaking. The diversity of mechanisms underlying the association between migraine and stroke likely reflects the heterogenous nature of this disorder. Vasospasm, endothelial injury, platelet aggregation and prothrombotic states, cortical spreading depression, carotid dissection, genetic variants, and traditional vascular risk factors have been offered as putative mechanisms involved in migraine-related stroke risk. Assimilating these seemingly divergent pathomechanisms into a cogent understanding of migraine-related stroke will inform future studies and the development of new strategies for the prevention and treatment of migraine and stroke.

Serotonin and CGRP in migraine

Migraine is defined as recurrent attack of headache that are commonly unilateral and accompanied by gastrointestinal and visual disorders. Migraine is more prevalent in females than males with a ratio of 3:1. It is primarily a complex neurovascular disorder involving local vasodilation of intracranial, extracerebral blood vessels and simultaneous stimulation of surrounding trigeminal sensory nervous pain pathway that results in headache. The activation of 'trigeminovascular system' causes release of various vasodilators, especially calcitonin gene-related peptide (CGRP) that induces pain response. At the same time, decreased levels of neurotransmitter, serotonin have been observed in migraineurs. Serotonin receptors have been found on the trigeminal nerve and cranial vessels and their agonists especially triptans prove effective in migraine treatment. It has been found that triptans act on trigeminovascular system and bring the elevated serum levels of key molecules like calcitonin gene related peptide (CGRP) to normal. Currently CGRP receptor antagonists, olcegepant and telcagepant are under consideration for antimigraine therapeutics. It has been observed that varying levels of ovarian hormones especially estrogen influence serotonin neurotransmission system and CGRP levels making women more predisposed to migraine attacks. This review provides comprehensive information about the role of serotonin and CGRP in migraine, specifically the menstrual migraine.

Inducible nitric oxide synthase haplotype associated with migraine and aura

Migraine is a complex neurological disorder with a clear neurogenic inflammatory component apparently including enhanced nitric oxide (NO) formation. Excessive NO amounts possibly contributing to migraine are derived from increased expression and activity of inducible NO synthase (iNOS). We tested the hypothesis that two functional, clinically relevant iNOS genetic polymorphisms (C(-1026)A-rs2779249 and G2087A-rs2297518) are associated with migraine with or without aura. We studied 142 healthy women without migraine (control group) and 200 women with migraine divided into two groups: 148 with migraine without aura (MWA) and 52 with aura (MA). Genotypes were determined by real-time polymerase chain reaction using the Taqman(®) allele discrimination assays. The PHASE 2.1 software was used to estimate the haplotypes. The A allele for the G2087A polymorphism was more commonly found in the MA group than in the MWA group (28 vs. 18%; P < 0.05). No other significant differences in the alleles or genotypes distributions were found (P > 0.05). The haplotype combining both A alleles for the two polymorphisms was more commonly found in the MA group than in the control group or in the MWA group (19 vs. 10 or 8%; P = 0.0245 or 0.0027, respectively). Our findings indicate that the G2087A and the C(-1026)A polymorphism in the iNOS gene affect the susceptibility to migraine with aura when their effects are combined within haplotypes, whereas the G2087A affects the susceptibility to aura in migraine patients. These finding may have therapeutic implications when examining the effects of selective iNOS inhibitors.

Head tremor related to CACNA1A mutations

Introduction: Familial hemiplegic migraine (FHM) is characterized by the familial occurrence of migraine attacks with fully reversible transient hemiplegia. Mutations in three different genes have been identified; CACNA1A (FHM1), ATP1A2 (FHM2) and SCN1A (FHM3). Besides hemiplegia, several other symptoms have been described in FHM 1–3 mutation carriers, including epilepsy and cerebellar symptoms.

Case report: We describe two patients in whom hemiplegic attacks were not the presenting symptom, but in whom an otherwise unexplained head tremor led us to search for FHM mutations. Both patients carried a mutation in the CACNA1A gene.

Discussion: CACNA1A mutations can give significant symptoms other than (hemiplegic) migraine as reason for presentation.

Lack of association between ADRA2B-4825 gene insertion/deletion polymorphism and migraine in Chinese Han population

OBJECTIVE

The present study aimed to estimate the association between susceptibility to migraine and the 12-nucleotide insertion/deletion (indel) polymorphism in promoter region of alpha(2B)-adrenergic receptor gene (ADRA2B).

METHODS

A case-control study was carried out in Chinese Han population, including 368 cases of migraine and 517 controls. Genomic DNA was extracted from blood samples, and DNA fragments containing the site of polymorphism were amplified by PCR. Data were adjusted for sex, age, migraine history and family history, and analyzed using a logistic regression model.

RESULTS

There was no association between indel polymorphism and migraine, at either the allele or the genotype level.

CONCLUSION

These findings do not support a functional significance of ADRA2B indel polymorphism at position -4825 relative to the start codon in the far upstream region of the promoter in the present migraine subjects.

Association of the pentanucleotide repeat polymorphism in NOS2 promoter region with susceptibility to migraine in a Chinese population

Genes involved in the production of nitric oxide (NO) have been suggested as genetic factors for migraine. It has been studied whether polymorphisms in the genes encoding for different types of NO synthase (NOS) could be involved in the liability to migraine; however, most studies yield negative results. The pentanucleotide repeat microsatellite in the promoter region of inducible NOS (NOS2) shows highly significant differences in allelic frequencies among ethnically diverse populations. Thus, variation in the number of pentanucleotide repeats may have some significance in the predisposition to migraine among different human populations. The aim of this study was to investigate the possible association between pentanucleotide repeat polymorphism and the risk for migraine in Chinese population. We studied the genotypic and allelic frequencies of the pentanucleotide repeat polymorphism in the promoter region of NOS2 in 504 patients with migraine and 512 healthy controls, using polymerase chain reaction amplification and polyacrylamide gel electrophoresis analyses. Comparison of global allele counts between patients and controls showed that the difference was significant (p = 0.0014). The carriage of 9-repeat and 10-repeat alleles was significantly more common in controls, whereas 11-repeat allele was more common in patients after Bonferroni correction for multiple comparisons. A specific analysis of the different cutoffs for number of repeats showed that allelic and genotypic frequencies for the 9-repeat and 10-repeat cutoff were significantly different between cases and controls (p = 0.007 and p = 0.005 for allelic frequencies, respectively; p = 0.0086 and p = 0.0033 for genotypic frequencies, respectively). Our results implied an association between NOS2 pentanucleotide repeat polymorphism and migraine susceptibility in a Chinese population. Considering the significant allelic frequency differences in ethnically diverse populations, further replication studies, especially in ethnically different groups, were necessary to fully establish the role of NOS2 polymorphism in migraine susceptibility.

A visual migraine aura locus maps to 9q21-q22

OBJECTIVE

To identify susceptibility loci for visual migraine aura in migraine families primarily affected with scintillating scotoma type of aura.

METHODS

We included Finnish migraine families with at least 2 affected family members with scintillating scotoma as defined by the International Criteria for Headache Disorders-II. A total of 36 multigenerational families containing 351 individuals were included, 185 of whom have visual aura and 159 have scintillating scotoma. Parametric and nonparametric linkage analyses were performed with 378 microsatellite markers. The most promising linkage loci found were fine-mapped with additional microsatellite markers.

RESULTS

A novel locus on chromosome 9q22-q31 for migraine aura was identified (HLOD = 4.7 at 104 cM). Fine-mapping identified a shared haplotype segment of 12 cM (9.8 Mb) on 9q21-q22 among the aura affected. Four other loci showed linkage to aura: a locus on 12p13 showed significant evidence of linkage, and suggestive evidence of linkage was detected to loci on chromosomes 5q13, 6q25, and 13q14.

CONCLUSIONS

A novel visual migraine aura locus has been mapped to chromosome 9q21-q22. Interestingly, this region has previously been linked to occipitotemporal lobe epilepsy with prominent visual symptoms. Our finding further supports a shared genetic background in migraine and epilepsy and suggests that susceptibility variant(s) to visual aura for both of these traits are located in the 9q21-q22 locus.

High cortical spreading depression susceptibility and migraine-associated symptoms in Ca(v)2.1 S218L mice

OBJECTIVE

The CACNA1A gene encodes the pore-forming subunit of neuronal Ca(V)2.1 Ca2+ channels. In patients, the S218L CACNA1A mutation causes a dramatic hemiplegic migraine syndrome that is associated with ataxia, seizures, and severe, sometimes fatal, brain edema often triggered by only a mild head trauma.

METHODS

We introduced the S218L mutation into the mouse Cacna1a gene and studied the mechanisms for the S218L syndrome by analyzing the phenotypic, molecular, and electrophysiological consequences.

RESULTS

Cacna1a(S218L) mice faithfully mimic the associated clinical features of the human S218L syndrome. S218L neurons exhibit a gene dosage-dependent negative shift in voltage dependence of Ca(V)2.1 channel activation, resulting in enhanced neurotransmitter release at the neuromuscular junction. Cacna1a(S218L) mice also display an exquisite sensitivity to cortical spreading depression (CSD), with a vastly reduced triggering threshold, an increased propagation velocity, and frequently multiple CSD events after a single stimulus. In contrast, mice bearing the R192Q CACNA1A mutation, which in humans causes a milder form of hemiplegic migraine, typically exhibit only a single CSD event after one triggering stimulus.

INTERPRETATION

The particularly low CSD threshold and the strong tendency to respond with multiple CSD events make the S218L cortex highly vulnerable to weak stimuli and may provide a mechanistic basis for the dramatic phenotype seen in S218L mice and patients. Thus, the S218L mouse model may prove a valuable tool to further elucidate mechanisms underlying migraine, seizures, ataxia, and trauma-triggered cerebral edema.

A young man presenting with acute encephalopathy, hemiparesis, and headache

BACKGROUND

Familial hemiplegic migraine (FHM) is a rare type of migraine. Correct diagnosis is challenging for emergency physicians (EPs) due to its variable clinical picture, as well as its lack of diagnostic biological markers.

OBJECTIVES

To raise awareness among EPs regarding FHM's diverse clinical picture, and to highlight FHM's diagnostic criteria to facilitate an accurate and timely diagnosis of FHM in patients presenting to the emergency department (ED) with indicative symptomatology.

CASE REPORT

A 24-year-old male student presented to the ED complaining of dizziness, general weakness, and blurred vision that had developed the previous night. The initial physical examination revealed drowsiness, slow speech production, and slight weakness with paresthesia in all limbs. Detailed communication with the patient's aunt revealed that he had experienced several similar attacks since the age of 12 years, and that there was also an extensive family history of the same symptoms. In addition, 2 h after arrival, the patient experienced severe throbbing headache, vomiting, severe dysphasia, and the weakness shifted to the right side. A computed tomography scan of the brain showed no anomalies. He was admitted with a tentative diagnosis of FHM.

CONCLUSION

A diagnosis of FHM should be considered if the patient's clinical features include headache and weakness, with a family history of similar symptomatology. However, atypical symptoms of FHM may present as recurrent episodes of unexplained encephalopathy. Crucial elements for making an accurate and timely diagnosis of FHM include a detailed knowledge of weakness-related diseases and an ability to consider FHM in the differential diagnosis, as well as obtaining a thorough family history with repeated neurologic assessments.

Visual paired-pulse stimulation reveals enhanced visual cortex excitability in migraineurs

Migraine is a common ictal disorder with an interindividual heterogeneous characteristic, whose underlying mechanisms remain elusive. On the one hand migraine is associated with abnormal cortical hyperexcitability. On the other hand, studies reported lower amplitudes of visual-evoked potentials (VEPs) and concluded that low preactivation levels imply decreased excitability. Here we measured visual cortex excitability and paired-pulse suppression in subjects suffering from migraine without aura and in a group of aged- and gender-matched healthy subjects to address the relation between activation levels and excitability. To that aim, we analysed amplitudes of VEPs and paired-pulse suppression evoked by a paired-pulse stimulation paradigm using stimulus onset asynchronies (SOAs) between 80 and 133 ms. We found that in migraineurs in the interictal state the amplitudes of the first VEP were reduced as compared with healthy subjects by approximately 20%. In the case of paired-pulse suppression comparable to healthy controls, the second response amplitude should be reduced as well, which was not the case. Instead, the ratio between the first and second VEP was higher than in healthy controls and did not depend on SOA in the range tested, which demonstrates reduced paired-pulse suppression and therefore implicates increased cortical excitability. Our data show that in migraineurs VEPs were reduced presumably due to reduced activation levels. However, paired-pulse suppression using short SOAs in the range of 100 ms or less was even higher than in normal subjects. Thus, our data show that signatures of both hyper- and hypoexcitability can be found depending on stimulation condition.

TREX1 acts in degrading damaged DNA from drug-treated tumor cells

The major mammalian exonuclease TREX1 has been proposed to play a role in DNA repair and drug resistance. However, no cellular evidence substantiates this claim. Recent reports indicate TREX1's involvement in autoimmunity. To further understand its role, we studied TREX1 expression and functionality in anticancer drug-treated tumor cells. We report that the expression and localization of TREX1 are cell-type dependent. Camptothecin and other DNA damaging agents induced both TREX1 protein and its mRNA in a dose- and time-dependent manner. Using a TREX1-inducible cell line, we performed clonogenic assays and found no change in sensitivity of the cells to the agents upon TREX1 induction, suggesting that TREX1 may not play a role in DNA repair or drug sensitivity. Nevertheless, TREX1 serves as a key enzyme in the degradation of DNA from dying cells leading to less cellular DNA. Ubiquitously expressed in normal tissues, TREX1 may act in degrading DNA in all cell types undergoing a dying process before phagocytosis occurs.

Molecular genetics of migraine

Migraine is an episodic neurovascular disorder that is clinically divided into two main subtypes that are based on the absence or presence of an aura: migraine without aura (MO) and migraine with aura (MA). Current molecular genetic insight into the pathophysiology of migraine predominantly comes from studies of a rare monogenic subtype of migraine with aura called familial hemiplegic migraine (FHM). Three FHM genes have been identified, which all encode ion transporters, suggesting that disturbances in ion and neurotransmitter balances in the brain are responsible for this migraine type, and possibly the common forms of migraine. Cellular and animal models expressing FHM mutations hint toward neuronal hyperexcitability as the likely underlying disease mechanism. Additional molecular insight into the pathophysiology of migraine may come from other monogenic syndromes (for instance cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, which is caused by NOTCH3 mutations), in which migraine is prominent. Investigating patients with common forms of migraine has had limited successes. Except for 5',10'-methylenetetrahydrolate reductase, an enzyme in folate metabolism, the large majority of reported genetic associations with candidate migraine genes have not been convincingly replicated. Genetic linkage studies using migraine subtypes as an end diagnosis did not yield gene variants thus far. Clinical heterogeneity in migraine diagnosis may have hampered the identification of such variants. Therefore, the recent introduction of more refined methods of phenotyping, such as latent-class analysis and trait component analysis, may be certainly helpful. Combining the new phenotyping methods with genome-wide association studies may be a successful strategy toward identification of migraine susceptibility genes. Likely the identification of reliable biomarkers for migraine diagnosing will make these efforts even more successful.

Profound encephalopathy with complete recovery in three children with familial hemiplegic migraine

We describe three cousins who presented with agitation, dysphasia and/or coma, and developed hemiplegia following initial onset of symptoms. Two cases followed minor head injuries, two were pyrexial and two were associated with neutrophilia. Two cases required ventilatory support on the intensive care unit. Magnetic resonance imaging in all three cases showed cortical swelling, and one had evidence of restricted water diffusion on diffusion-weighted imaging, suggestive of ischaemia/infarction. A complete family history at the time of presentation would have led to an earlier diagnosis of profound encephalopathy in familial hemiplegic migraine, which would have enabled better prognostication of their clinical course and caused less distress for the families.

The relationship between migraine and mental disorders in a population-based sample

OBJECTIVE

There is emerging evidence from clinical and community samples to suggest that migraines are associated with mental disorders. The present study utilized a large population-based sample to investigate the association between physician-diagnosed migraine and mental disorders.

METHOD

Data were from the German Health Survey conducted between 1997 and 1999 (N=4181, response rate 61.4%, age 18-65 years). Lifetime and 12-month history of migraines were assessed by self-report and by a physician. Past 12-month DSM-IV mental disorders were assessed using the Composite International Diagnostic Interview.

RESULTS

After adjusting for sociodemographic factors, past-year migraine was significantly and positively associated with depression, dysthymia, bipolar disorder, panic attacks, panic disorder, agoraphobia and simple phobia [adjusted odds ratios (AOR) ranging from 1.74 to 3.21]. After additionally adjusting for other mental disorders, any anxiety disorder (AOR=1.82) and any mood disorder (AOR=1.61) remained significantly associated with past-year migraine.

CONCLUSION

Although causal inferences cannot be made due to the cross-sectional nature of the data, the present study adds to a growing body of literature that suggests a strong association between migraines and mood and anxiety disorders.

Migraine and epilepsy: genetically linked?

Most molecular genetic knowledge in migraine so far comes from the study of a rare subtype, familial hemiplegic migraine (FHM). The three known FHM genes (CACNA1A, ATP1A2 and SCN1A) are ion transporter genes. Mutations in all three FHM genes can also be associated with epilepsy. Of the many epilepsy genes that have been discovered, an association with migraine has been reported only for SCN1A. There is probably a lack of systematic studies of migraine in epilepsy families. A genetically determined dysfunction of ion transporters seems to point, at least to certain extent, at a common underlying mechanism for both paroxysmal disorders. The effect of ion channel mutations on neuronal neurotransmitter release is probably of major importance. In this article, we will discuss the arguments for a genetic relationship between migraine and epilepsy. A possible genetic link could give insight into the pathophysiology of both syndromes, and offer possibilities to develop specific preventive treatment aimed at the underlying ion transporter dysfunction and its consequences.