Familial hemiplegic migraine locus on 19p13 is involved in the common forms of migraine with and without aura

Pathophysiology of Migraine: A Disorder of Sensory Processing

Plaguing humans for more than two millennia, manifest on every continent studied, and with more than one billion patients having an attack in any year, migraine stands as the sixth most common cause of disability on the planet. The pathophysiology of migraine has emerged from a historical consideration of the "humors" through mid-20th century distraction of the now defunct Vascular Theory to a clear place as a neurological disorder. It could be said there are three questions: why, how, and when? Why: migraine is largely accepted to be an inherited tendency for the brain to lose control of its inputs. How: the now classical trigeminal durovascular afferent pathway has been explored in laboratory and clinic; interrogated with immunohistochemistry to functional brain imaging to offer a roadmap of the attack. When: migraine attacks emerge due to a disorder of brain sensory processing that itself likely cycles, influenced by genetics and the environment. In the first, premonitory, phase that precedes headache, brain stem and diencephalic systems modulating afferent signals, light-photophobia or sound-phonophobia, begin to dysfunction and eventually to evolve to the pain phase and with time the resolution or postdromal phase. Understanding the biology of migraine through careful bench-based research has led to major classes of therapeutics being identified: triptans, serotonin 5-HT1B/1D receptor agonists; gepants, calcitonin gene-related peptide (CGRP) receptor antagonists; ditans, 5-HT1F receptor agonists, CGRP mechanisms monoclonal antibodies; and glurants, mGlu5 modulators; with the promise of more to come. Investment in understanding migraine has been very successful and leaves us at a new dawn, able to transform its impact on a global scale, as well as understand fundamental aspects of human biology.

Vestibular Migraine: Clinical Challenges and Opportunities for Multidisciplinarity

Migraine and vertigo are two very prevalent conditions in general population. The coexistence of both in the same subject is a significant clinical challenge, since it is not always possible to understand whether they are causally related or associated by chance, requiring different diagnostic and therapeutic approaches. In this review we analyze and summarize the actual knowledge about vestibular migraine (VM), focusing on the new concepts proposed by the International Classification of Headache Disorders 3-beta and by the Bárány Society and also addressing the former concepts, which are still present in clinical practice. We conclude that clinical studies using a multidisciplinary approach are crucial in this field, since different specialists observe the same pathology with different eyes. Clinical presentation of VM is variable in what concerns vestibular symptoms temporal relation with migraine headache, as well as in their accompanying manifestations. Biomarkers, either genomics or functional, and molecular imaging techniques will be helpful to clarify many aspects of the complexity of this entity, helping to define to what extent can VM be considered a separate and independent clinical entity.

Familial occurrence of headache disorders: A population-based study in mainland China

BACKGROUND

Headache disorders are highly prevalent worldwide, and familial occurrence and heredity are contributory factors attracting the interest of epidemiological researchers. Our purpose, in a large sample drawn nationwide from the Chinese general population, was to evaluate the frequency of similar headache in first-degree relatives (FDRs) of those with different headache types.

METHODS

This was a questionnaire-based nationwide cross-sectional door-to-door survey using cluster random-sampling, selecting one adult (18-65 years) per household. Headache was diagnosed by ICHD-II criteria. Participants with headache were asked whether or not any FDRs had similar headache to their own. Chi-squared test and multivariate logistic regression analysis were used to assess the strength and significance of associations.

RESULTS

Of 5041 survey participants (participation rate 94.1%), 1060 (21.0%) were diagnosed with headache (migraine 469 [9.3%], tension-type headache [TTH] 543 [10.8%], headache on ≥15 days/month 48 [0.95%]). From these, 31 were excluded because of missing data about FDRs, leaving 1029 for analysis (male 350 [mean age: 46.7±11.4years]; female 679 [mean age 46.3±11.2years]). Similar headache in one or more FDRs was reported by 22.2% (95% CI: 19.6-24.7%) overall, by 25.1% (21.1-29.1%) of those with migraine, by 19.1% (15.7-22.4%) with TTH and by 29.2% (16.3-42.0%) with headache on ≥15 days/month. The differences was significant between migraine and TTH (OR=1.4, p=0.023), but were not significant between headache on ≥15 days/month and TTH (OR=1.7, p=0.093), migraine and headache on ≥15 days/month (OR=1.2,p=0.534). In multivariate analysis: for migraine versus TTH,AOR=1.2 (p=0.015); for headache on ≥15 days/month versus TTH, AOR 2.3 (p=0.018).

CONCLUSION

Headache was highly prevalent in China and common among FDRs of those with any type of headache (headache on ≥15 days/month>migraine>TTH). Against the background of the general-population prevalence of each disorder, familial occurrence was a very highly influential factor in headache on ≥15 days/month. There are important implications in this for public health and education.

Preventive Treatment of Migraine: Effect on Weight

Weight gain is a side-effect commonly associated with drugs used for headache prophylaxis. Weight gain can adversely affect patient health, exacerbate comorbid metabolic disorders and encourage noncompliance. Few studies have been conducted specifically on the effect of headache medications on weight, and it is important for physicians to have accurate information about weight-gain side-effects when identifying appropriate pharmacological regimens. This review discusses the potential effects on weight of the more common headache medications.

Dopamine and Migraine: Biology and Clinical Implications

In the last 30 years dopamine has been considered as playing a role in the pathogenesis of migraine. The literature indicates that migraineurs are hypersensitive to dopamine agonists with respect to some of the premonitory symptoms of migraine such as nausea and yawning. There are various nonspecific dopamine D2 receptor antagonists that show good clinical efficacy in migraine, and also a number of polymorphisms of dopaminergic genes related to migraine. Animal studies have also shown that dopamine receptors are present in the trigeminovascular system, the area believed to be involved in headache pain, and neuronal firing here is reduced by dopamine agonists. There appears to be little effect of dopamine on peripheral trigeminal afferents. We assess some of the limitations of the clinical studies with regard to the therapeutics, and those found in the studies that discovered differences in genetic polymorphisms in migraine, and consider the implications of this on a dopaminergic hypothesis of migraine.

Subclinical Neuromuscular Transmission Abnormality Detected by Single-Fibre EMG is More Pronounced in Cluster Headache Than in Migraine With Aura

The aim was to investigate neuromuscular transmission (NMT) by single-fibre EMG (SFEMG) in a large series of patients having migraine with aura (MA) or cluster headache (CH). Recent studies using SFEMG have shown subclinical dysfunction of NMT in MA and CH. Forty-three patients having MA, 51 with CH and 38 healthy control subjects underwent nerve conduction studies, EMG and SFEMG during voluntary contraction of the extensor digitorum communis muscle. Twenty different potential pairs were recorded and individual, mean and total abnormal individual jitter values were calculated. The results obtained from MA patients were compared with those from CH patients. In MA patients, 32 of 860 jitters were abnormally high, whereas 73 of 1020 of the jitters showed this abnormality in CH patients. None of the control subjects, five MA patients (11.6%) and 11 CH patients (21.6%) were designated as having subclinical NMT abnormality. Thus, patients having junction dysfunction were significantly more common in the CH group. The subclinical NMT abnormality shown by SFEMG is more common in CH than in MA. These two primary headache syndromes may have some shared functional abnormality of NMT constituents which is more evident in CH.

Migraine genetics: current findings and future lines of research

In the last two decades, migraine research has greatly advanced our current knowledge of the genetic contributions and the pathophysiology of this common and debilitating disorder. Nonetheless, this knowledge still needs to grow further and to translate into more effective treatments. To date, several genes involved in syndromic and monogenic forms of migraine have been identified, allowing the generation of animal models which have significantly contributed to current knowledge of the mechanisms underlying these rare forms of migraine. Common forms of migraine are instead posing a greater challenge, as they may most often stem from complex interactions between multiple common genetic variants, with environmental triggers. This paper reviews our current understanding of migraine genetics, moving from syndromic and monogenic forms to oligogenic/polygenic migraines most recently addressed with some success through genome-wide association studies. Methodological issues in study design and future perspectives opened by biomarker research will also be briefly addressed.

Vestibular migraine

Background

The combination of vertigo, dizziness and balance disturbance with migraine is called vestibular migraine. Although it is estimated that up to 1% of the population suffers from this disease, it is still widely unknown and often underdiagnosed. Recently, the International Headache Society and the Báràny Society published the first joint document with mutually accepted diagnostic criteria for vestibular migraine.

Method

This review summarizes current knowledge on vestibular migraine with regard to epidemiology, clinical presentation, pathophysiology, differential diagnosis and therapeutic options.

Results

Approximately 30–50% of patients with migraine report vertigo, dizziness or balance disturbances with at least one migraine attack. Vestibular migraine often appears in a temporal delay to the first onset of migraine headache. In some patients the symptom of sudden onset disequilibrium was the main complaint and more worrisome than the accompanying migraine headache. The duration of attacks varies from a few seconds up to few days. The underlying pathophysiology of vestibular migraine is still widely unknown. As an important differential diagnosis, Ménière’s disease has to be considered and excluded.

Conclusion

As randomized controlled treatment trials are still missing in vestibular migraine, the therapeutic recommendations for vestibular migraine are currently based on the guidelines of migraine.

Analysis of chromosome 1 microsatellite markers and the FHM2-ATP1A2gene mutations in migraine pedigrees

OBJECTIVES

The aims of the study were: (i) to extend our linkage analysis of chromosome 1q microsatellite markers in predominantly migraine with aura pedigrees and (ii) to test the novel FHM-2 ATP1A2 gene for involvement in these migraine affected pedigrees and a previous pedigree (MF14) showing evidence of linkage of markers to C1q31.

METHODS

A chromosome 1 scan (31 markers) was performed in 21 multiplex pedigrees affected predominantly with migraine with aura (MA). The known FHM-2 ATP1A2 gene mutations were tested, by sequencing, for the involvement in MA and migraine without aura (MO) in these pedigrees. Sequencing was performed in the coding areas of the ATP1A2 gene through three MA individuals from MF14.

RESULTS

Evidence for linkage was obtained at C1q23 to markers spanning the ATP1A2 gene. However, testing of the known ATP1A2 gene mutations (for FHM) in common migraine probands of pedigrees showing excess allele sharing was negative. Sequencing of the entire coding areas of the gene through all the three MA affected from MF14 was also negative for mutations.

DISCUSSION

Microsatellite markers on chromosome 1q23 show evidence of excess allele sharing in MA and some MO pedigrees, suggesting linkage to the common forms of migraine and the presence of a susceptibility gene in this region. The FHM-2 (ATP1A2 gene) does not seem to be involved in the common types of migraine. Despite certain clinical characteristics, the genetic correlation between FHM and familial typical migraine remains unclear. Several candidate genes lie within the C1q23 and C1q31 cytogenetic regions; therefore, further studies are needed.

Where does a migraine attack originate? In the brainstem

Migraine is a common, paroxysmal, highly disabling primary headache disorder. The origin of migraine attacks is enigmatic. Numerous clinical and experimental results suggest that the activation of distinct brainstem nuclei is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. We conclude that the initialization of a migraine attack can be explained as an altered function of the neuronal elements of the brainstem nuclei. In light of our findings and the literature data, we can assume that migraine is a subcortical disorder of a specific brainstem area.

Migraine With Aura and Migraine Without Aura Are Not Distinct Entities: Further Evidence From a Large Dutch Population Study

It is often debated whether migraine with aura (MA) and migraine without aura (MO) are etiologically distinct disorders. A previous study using latent class analysis (LCA) in Australian twins showed no evidence for separate subtypes of MO and MA. The aim of the present study was to replicate these results in a population of Dutch twins and their parents, siblings and partners (N = 10,144). Latent class analysis of International Headache Society (IHS)-based migraine symptoms resulted in the identification of 4 classes: a class of unaffected subjects (class 0), a mild form of nonmigrainous headache (class 1), a moderately severe type of migraine (class 2), typically without neurological symptoms or aura (8% reporting aura symptoms), and a severe type of migraine (class 3), typically with neurological symptoms, and aura symptoms in approximately half of the cases. Given the overlap of neurological symptoms and nonmutual exclusivity of aura symptoms, these results do not support the MO and MA subtypes as being etiologically distinct. The heritability in female twins of migraine based on LCA classification was estimated at .50 (95% confidence intervals [CI] .27 – .59), similar to IHS-based migraine diagnosis (h2 = .49, 95% CI .19–.57). However, using a dichotomous classification (affected–unaffected) decreased heritability for the IHS-based classification (h2 = .33, 95% CI .00–.60), but not the LCA-based classification (h2 = .51, 95% CI .23–.61). Importantly, use of the LCA-based classification increased the number of subjects classified as affected. The heritability of the screening question was similar to more detailed LCA and IHS classifications, suggesting that the screening procedure is an important determining factor in genetic studies of migraine.

Genetic aspects of familial Ménière's disease

OBJECTIVE

Ménière's disease (MD) is a chronic illness characterized by sensorineural hearing loss, recurring vertigo attacks, and tinnitus. It is possibly of multifactorial origin, although several families with autosomal dominant inheritance and reduced penetrance have been described. To elucidate the genetic basis of MD, patients and their families were investigated, and linkage analysis was performed.

STUDY DESIGN

Retrospective and prospective family survey.

PATIENTS AND METHODS

Of 193 patients diagnosed with MD, 37 patients could be ascertained as having a positive family history, which means a frequency of 19.2%. Nineteen families with 81 members (52 positive for MD and 29 negative for MD) were investigated according to the guidelines of the Committee on Hearing and Equilibrium of the American Academy of Otolaryngology. Blood samples were obtained, and a genome-wide linkage analysis was performed with microsatellite markers.

RESULTS

Age of onset diminished in subsequent generations. We found suggestive evidence of linkage assuming heterogeneity of MD on chromosome 5 with a maximum multipoint logarithm of the odds of linkage (LOD) score of 1.9 for 13 of 17 families and a potential region on chromosome 12 for 8 families. Of the 81 subjects, 27 (33.3%) reported MD only, 25 (30.9%) reported migraine and MD, and 7 (8.6%) reported migraine only.

CONCLUSION

Family trees suggest an autosomal dominant inheritance with reduced penetrance and anticipation. A probable candidate region for MD was located on chromosome 5.

One hundred years of migraine research: major clinical and scientific observations from 1910 to 2010

Pain research, and headache research in particular, during the 20th century, has generated an enormous volume of literature promulgating theories, questions, and temporary answers. This narrative review describes the most important events in the history of migraine research between 1910 and 2010. Based on the standard textbooks of headache: Wolff's Headache (1948 and 1963) and The Headaches (1993, 2000, and 2006) topics were selected for a historical review. Most notably these included: isolation and clinical introduction of ergotamine (1918); further establishment of vasodilation in migraine and the constrictive action of ergotamine (1938); identification of pain-sensitive structures in the head (1941); Lashley's description of spreading scotoma (1941); cortical spreading depression (CSD) of Leão (1944); serotonin and the introduction of methysergide (1959); spreading oligemia in migraine with aura (1981); oligemia in the wake of CSD in rats (1982); neurogenic inflammation theory of migraine (1987); a new headache classification (1988); the discovery of sumatriptan (1988); migraine and calcitonin gene-related peptide (1990); the brainstem "migraine generator" and PET studies (1995); migraine as a channelopathy, including research from the genetic perspective (1996); and finally, meningeal sensitization, central sensitization, and allodynia (1996). Pathophysiological ideas have evolved within a limited number of paradigms, notably the vascular, neurogenic, neurotransmitter, and genetic/molecular biological paradigm. The application of various new technologies played an important role within these paradigms, in particular neurosurgical techniques, EEG, methods to measure cerebral blood flow, PET imaging, clinical epidemiological, genetic, and molecular biological methods, the latter putting migraine (at least hemiplegic migraine) within a completely new classification of diseases.

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.

Migraine genetics

Migraine with aura (MA) and migraine without aura (MO) are primary headaches prevalent in the general population that carry a substantial familial liability. Based on the model of migraine as a complex disease, a multifactorial type of inheritance has been suggested, but familial hemiplegic migraine (FHM), classified as a subtype of MA, shows an autosomal dominant transmission pattern and is due to mutations in three genes encoding for neural channel subunits. These FHM mutations, however, account for a minority of the FHM families and are not usually found in sporadic HM or in the typical migraines MA/MO. This implies that the genetic predisposition to the typical migraines may be different and that FHM could be better classified as a type of syndromic migraine rather than a MA subtype. Linkage and genome-wide scans have disclosed several chromosomal liability loci in selected families with MA/MO. It is likely that typical migraine genes will be discovered in the future. Epigenetic mechanisms, especially those acting in the early stages of neural development, are here proposed to be involved in the genetics of the typical migraines, especially if the typical migraines are modeled as evolutionarily conserved behaviors (sickness behavior) enacted out of a genetic repertoire.

A genome-wide linkage scan provides evidence for both new and previously reported loci influencing common migraine

Latent class analysis was performed on migraine symptom data collected in a Dutch population sample (N = 12,210, 59% female) in order to obtain empirical groupings of individuals suffering from symptoms of migraine headache. Based on these heritable groupings (h(2) = 0.49, 95% CI: 0.41-0.57) individuals were classified as affected (migrainous headache) or unaffected. Genome-wide linkage analysis was performed using genotype data from 105 families with at least 2 affected siblings. In addition to this primary phenotype, linkage analyses were performed for the individual migraine symptoms. Significance levels, corrected for the analysis of multiple traits, were determined empirically via a novel simulation approach. Suggestive linkage for migrainous headache was found on chromosomes 1 (LOD = 1.63; pointwise P = 0.0031), 13 (LOD = 1.63; P = 0.0031), and 20 (LOD = 1.85; P = 0.0018). Interestingly, the chromosome 1 peak was located close to the ATP1A2 gene, associated with familial hemiplegic migraine type 2 (FHM2). Individual symptom analysis produced a LOD score of 1.97 (P = 0.0013) on chromosome 5 (photo/phonophobia), a LOD score of 2.13 (P = 0.0009) on chromosome 10 (moderate/severe pain intensity) and a near significant LOD score of 3.31 (P = 0.00005) on chromosome 13 (pulsating headache). These peaks were all located near regions previously reported in migraine linkage studies. Our results provide important replication and support for the presence of migraine susceptibility genes within these regions, and further support the utility of an LCA-based phenotyping approach and analysis of individual symptoms in migraine genetic research. Additionally, our novel "2-step" analysis and simulation approach provides a powerful means to investigate linkage to individual trait components.

A novel ATP1A2 gene mutation in an Irish familial hemiplegic migraine kindred

OBJECTIVE

We studied a large Irish Caucasian pedigree with familial hemiplegic migraine (FHM) with the aim of finding the causative gene mutation.

BACKGROUND

FHM is a rare autosomal-dominant subtype of migraine with aura, which is linked to 4 loci on chromosomes 19p13, 1q23, 2q24, and 1q31. The mutations responsible for hemiplegic migraine have been described in the CACNA1A gene (chromosome 19p13), ATP1A2 gene (chromosome 1q23), and SCN1A gene (chromosome 2q24).

METHODS

We performed linkage analyses in this family for chromosome 1q23 and performed mutation analysis of the ATP1A2 gene.

RESULTS

Linkage to the FHM2 locus on chromosome 1 was demonstrated. Mutation screening of the ATP1A2 gene revealed a G to C substitution in exon 22 resulting in a novel protein variant, D999H, which co-segregates with FHM within this pedigree and is absent in 50 unaffected individuals. This residue is also highly conserved across species.

CONCLUSIONS

We propose that D999H is a novel FHM ATP1A2 mutation.

The primary headaches: genetics, epigenetics and a behavioural genetic model

The primary headaches, migraine with (MA) and without aura (MO) and cluster headache, all carry a substantial genetic liability. Familial hemiplegic migraine (FHM), an autosomal dominant mendelian disorder classified as a subtype of MA, is due to mutations in genes encoding neural channel subunits. MA/MO are considered multifactorial genetic disorders, and FHM has been proposed as a model for migraine aetiology. However, a review of the genetic studies suggests that the FHM genes are not involved in the typical migraines and that FHM should be considered as a syndromic migraine rather than a subtype of MA. Adopting the concept of syndromic migraine could be useful in understanding migraine pathogenesis. We hypothesise that epigenetic mechanisms play an important role in headache pathogenesis. A behavioural model is proposed, whereby the primary headaches are construed as behaviours, not symptoms, evolutionarily conserved for their adaptive value and engendered out of a genetic repertoire by a network of pattern generators present in the brain and signalling homeostatic imbalance. This behavioural model could be incorporated into migraine genetic research.

Evaluation and proposal for optimalization of neurophysiological tests in migraine: part 1--electrophysiological tests

Neurophysiological testing has become a valuable tool for investigating brain excitability and nociceptive systems in headache disorders. Previous reviews have suggested that most neurophysiological tests have limited value for headache diagnosis, but a vast potential for exploring the pathophysiology of headaches, the central effects of certain pharmacological treatments and phenotype-genotype correlations. Many protocols, however, lack standardization. This meta-analytical review of neurophysiological methods in migraine was initiated by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9). Most of the neurophysiological approaches that have been used in headache patients are reviewed, i.e. evoked potentials, nociception-specific blink reflex, single-fibre electromyography, neuroimaging methods (functional MRI, PET, and voxel-based morphometry) and the nitroglycerin attack-provoking test. For each of them, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols. The first part is devoted to electrophysiological methods, the second to neuroimaging techniques and the NTG test.

Migraine: a complex genetic disorder

Although family and twin studies show that there is a genetic component to migraine, no genes predisposing to common forms of the disorder have been identified. The most encouraging findings have emerged from the identification of genes causing rare mendelian traits that phenotypically resemble migraine. These studies have pointed migraine research towards ion-transport genes; however, there is no direct evidence of the involvement of these genes in common forms of migraine. Family-based linkage studies have identified several chromosomal regions linked to common forms of migraine, but there is little consistency between studies. The modest success in the identification of contributing gene variants has stimulated research into more effective strategies. These include new phenotyping methods for genetic studies and new study designs-such as case-control and whole-genome association studies-to identify common variants contributing to the trait.

Channeling studies in yeast: yeast as a model for channelopathies?

Regulation of the concentration of ions within a cell is mediated by their specific transport and sequestration across cellular membranes. This regulation constitutes a major factor in the maintenance of correct cellular homeostasis, with the transport occurring through the action of a large number of different channel proteins localized to the plasma membrane as well as to various organelles. These ion channels vary in specificity from broad (cationic vs anionic) to highly selective (chloride vs sodium). Mutations in many of these channels result in a large number of human diseases, collectively termed channelopathies. Characterization of many of these channels has been undertaken in a variety of both prokaryotic and eukaryotic organisms. Among these organisms is the budding yeast Saccharomyces cerevisiae. Possessing a fully annotated genome, S. cerevisiae would appear to be an ideal organism in which to study this class of proteins associated to diseases. We have compiled and reviewed a list of yeast ion channels, each possessing a human homolog implicated in a channelopathy. Although yeast has been used for the study of other human disease, it has been under utilized for channelopathy research. The utility of using yeast as a model system for studying ion channels associated to human disease is illustrated using yeast lacking the GEF1 gene product that encodes the human homolog to the chloride channel CLC-3.

Genetic biomarkers for migraine

Biomarkers are physical signs or laboratory measurements that occur in association with a pathological process and have putative diagnostic and/or prognostic utility. In migraine, clinical, radiological, and biochemical biomarkers might be helpful to improve diagnosis, get insight in pathophysiology, and facilitate treatment choices. Genetic biomarkers are defined as genetic variations (mutations or polymorphisms) that can predict disease susceptibility, disease outcome, or treatment response. As yet, only a few genetic biomarkers for migraine are available. Mutations in 3 different genes responsible for familial hemiplegic migraine, a monogenetic subtype of migraine with aura, and the MTHFR C677T polymorphism in common forms of migraine are clear examples. Many positive findings from linkage studies and association studies in common forms of migraine have not been replicated, and are therefore of less clinical use. In this review, we will discuss genetic biomarkers in migraine.

Genetics of Migraine: An Update

Observations including the long-recognized tendency of migraine to run in families, the high concordance rates for migraine in twins reared together or apart, and the association of specific mutations with a rare migraine form are consistent with a genetic contribution to the disorder. This paper summarizes major findings to date on the genetics of migraine. Study of the heritability of migraine, particularly the common forms of migraine, is beset by several challenges including the absence of easily measurable biological markers, uncertainty about the etiologic and clinical overlap among migraine types, and the apparently complex interplay of environmental and genetic factors in determining migraine phenotype. Nevertheless, significant progress has been realized in recent years. Familial hemiplegic migraine, a rare migraine variant, appears to be transmitted by a Mendelian, autosomal dominant mode of inheritance involving mutations in at least 2 genes. These genes do not seem to be critically involved in the other forms of migraine; however, several other susceptibility loci for more common forms of migraine have been identified in recent genome-wide screens and candidate-locus studies. These and other data suggest that the genetic contribution to migraine is complex, multifactorial, and subject to significant modification by environmental factors.

Migraine: new treatment options from molecular biology

Migraine is a common, disabling, multifactorial, episodic neurovascular disorder of largely unknown etiology. The disease is typically characterized by recurrent attacks of headaches and associated autonomic and neurologic symptoms. Current acute and prophylactic treatment options are far from optimal and in many cases, empirically chosen. Clearly, improved treatment is desperately needed. New drug targets may emerge from molecular research as the unravelling of the molecular basis of migraine should improve our understanding of the disease, notably why patients experience attacks so frequently. The first two migraine genes discovered in families with hemiplegic migraine encode ion transporters, emphasising that dysfunction of ion transport may be an important factor in migraine. Therefore, ion transporters can be considered as novel targets for the development of future antimigraine drugs. Molecular biologic research will increasingly become important in understanding the pathophysiology of migraine and in identifying potential molecular targets for novel treatments.

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.

Exclusion of the juvenile myoclonic epilepsy gene EFHC1 as the cause of migraine on chromosome 6, but association to two rare polymorphisms in MEP1A and RHAG

Migraine is a complex, multifactorial disorder for which several loci have been identified in the human genome. We have previously reported linkage to a 10 Mb-region on chromosome 6p12.2-p21.1 in one large Swedish pedigree involving migraine with and without aura. To further investigate this candidate region, a dense set of single nucleotide polymorphic (SNP) markers was used for fine-mapping, decreasing the critical region to 8.5 Mb. Within this region, EFHC1 was recently identified as the disease gene for juvenile myoclonic epilepsy. Migraine and epilepsy has been suggested to share disease mechanisms and therefore EFHC1 is an excellent candidate gene for migraine in this family. Mutation analysis of the gene revealed a disease-segregating polymorphism in the promoter. Association analysis of the polymorphism in a case-control material did not support a role for this gene in migraine pathology. We therefore analyzed five additional candidate genes in the disease-critical region, including MEP1A, RHAG, IL17, SLC25A27 and TNFRSF21. In two of these genes, MEP1A and RHAG, we identified two novel polymorphisms associated with the disease haplotype. The combination of these polymorphisms could not be found in any control individuals, suggesting that they might be involved in genetic predisposition to migraine in this family.

No mutations detected in the INSR gene in a chromosome 19p13 linked migraine pedigree

The aim of this study was to investigate through direct sequencing the insulin receptor (INSR) gene in DNA samples from a migraine affected family previously showing linkage to chromosome 19p13 in an attempt to detect disease associated mutations. Migraine is a common debilitating disorder with a significant genetic component. At present, the number and type of genes involved in the common forms of migraine are not clear. The INSR gene on chromosome 19p13.3-13.2 is a gene of interest since a number of single nucleotide polymorphisms (SNPs) located within the gene have been implicated in migraine with (MA) and without aura (MO). Six DNA samples obtained from non-founding migraine affected members of migraine family 1 (MF1) were used in this study. Genomic DNA was sequenced for the INSR gene in exons 1-22 and the promoter region. In the six migraine family member samples, previously reported SNPs were detected within two exonic DNA coding regions of the INSR gene. These SNPs, in exons 13 and 17, do not alter the normal INSR polypeptide sequence. In addition, intron 7 also revealed a DNA base sequence variation. For the 5' untranslated promoter region of the gene, no mutations or polymorphisms were detected. In conclusion, this study detected no INSR mutations in affected members of a chromosome 19 linked migraine pedigree. Hence, migraine linkage to this chromosomal region may involve other candidate genes.

Genomewide significant linkage to migrainous headache on chromosome 5q21

Familial typical migraine is a common, complex disorder that shows strong familial aggregation. Using latent-class analysis (LCA), we identified subgroups of people with migraine/severe headache in a community sample of 12,245 Australian twins (60% female), drawn from two cohorts of individuals aged 23-90 years who completed an interview based on International Headache Society criteria. We report results from genomewide linkage analyses involving 756 twin families containing a total of 790 independent sib pairs (130 affected concordant, 324 discordant, and 336 unaffected concordant for LCA-derived migraine). Quantitative-trait linkage analysis produced evidence of significant linkage on chromosome 5q21 and suggestive linkage on chromosomes 8, 10, and 13. In addition, we replicated previously reported typical-migraine susceptibility loci on chromosomes 6p12.2-p21.1 and 1q21-q23, the latter being within 3 cM of the rare autosomal dominant familial hemiplegic migraine gene (ATP1A2), a finding which potentially implicates ATP1A2 in familial typical migraine for the first time. Linkage analyses of individual migraine symptoms for our six most interesting chromosomes provide tantalizing hints of the phenotypic and genetic complexity of migraine. Specifically, the chromosome 1 locus is most associated with phonophobia; the chromosome 5 peak is predominantly associated with pulsating headache; the chromosome 6 locus is associated with activity-prohibiting headache and photophobia; the chromosome 8 locus is associated with nausea/vomiting and moderate/severe headache; the chromosome 10 peak is most associated with phonophobia and photophobia; and the chromosome 13 peak is completely due to association with photophobia. These results will prove to be invaluable in the design and analysis of future linkage and linkage disequilibrium studies of migraine.

Chromosome 19p13 loci in Finnish migraine with aura families

Chromosomal area 19p13 contains two migraine associated genes: a Ca(v)2.1 (P/Q-type) calcium channel alpha(1) subunit gene, CACNA1A, and an insulin receptor gene, INSR. Missense mutations in CACNA1A cause a rare Mendelian form of migraine, familial hemiplegic migraine type 1 (FHM1). Contribution of CACNA1A locus has also been studied in the common forms of migraine, migraine with (MA) and without aura (MO), but the results have been contradictory. The role of INSR is less well established: A region on 19p13 separate from CACNA1A was recently reported to be a major locus for migraine and subsequently, the INSR gene was associated with MA and MO. Our aim was to clarify the role of these loci in MA families by analyzing 72 multigenerational Finnish MA families, the largest family sample so far. We hypothesized that the potential major contribution of the 19p13 loci should be detected in a family sample of this size, and this was confirmed by simulations. We genotyped eight polymorphic microsatellite markers surrounding the INSR and CACNA1A genes on 757 individuals. Using parametric and non-parametric linkage analysis, none of the studied markers showed any evidence of linkage to MA either under locus homogeneity or heterogeneity. However, marginally positive lod scores were observed in three families, and thus for these families the results remain inconclusive. The overall conclusion is that our study did not provide evidence of a major MA susceptibility region on 19p13 and thus we were not able to replicate the INSR locus finding.

Investigation of the low-density lipoprotein receptor gene and cholesterol as a risk factor for migraine

The Low-Density Lipoprotein Receptor (LDLR) gene is a cell surface receptor that plays an important role in cholesterol homeostasis. We investigated the (TA)n polymorphism in exon 18 of the LDLR gene on chromosome 19p13.2 performing an association analysis in 244 typical migraine-affected patients, 151 suffering from migraine with aura (MA), 96 with migraine without aura (MO) and 244 unaffected controls. The populations consisted of Caucasians only, and controls were age- and sex-matched. The results showed no significant difference between groups for allele frequency distributions of the (TA)n polymorphism even after separation of the migraine-affected individuals into subgroups of MA and MO affected patients. This is in contradiction to Mochi et al. who found a positive association of this variant with MO. Our study discusses possible differences between the two studies and extends this research by investigating circulating cholesterol levels in a migraine-affected population.

Vertigo and dizziness related to migraine: a diagnostic challenge

Vertigo and dizziness can be related to migraine in various ways: causally, statistically or, quite frequently, just by chance. Migrainous vertigo (MV) is a vestibular syndrome caused by migraine and presents with attacks of spontaneous or positional vertigo lasting seconds to days and migrainous symptoms during the attack. MV is the most common cause of spontaneous recurrent vertigo and is presently not included in the International Headache Society classification of migraine. Benign paroxysmal positional vertigo (BPPV) and Ménière's disease (MD) are statistically related to migraine, but the possible pathogenetic links have not been established. Moreover, migraineurs suffer from motion sickness more often than controls. Persistent cerebellar symptoms may develop in the course of familial hemiplegic migraine. Dizziness may also be due to orthostatic hypotension, anxiety disorders or major depression which all have an increased prevalence in patients with migraine.

Genetic Epidemiology of Neurologic Disease

This chapter begins with a discussion of Mendelian versus complex (non-Mendelian) neurological disorders, followed by an overview of the structure of DNA and the molecular basis of disease. It considers the methods of genetic epidemiology, differentiating family-based studies from population-based studies of unaffected individuals. The options for genetic epidemiology study designs are presented, with a discussion of strengths and limitations of each approach. Recent technological developments are discussed, as are the important ethical and social implications of genetic epidemiologic research in the study of neurological disorders.

The molecular genetics of migraine

Within the past decade it has been possible to identify susceptibility gene loci that predispose to migraine using genetic markers distributed across the human genome. Five new loci with significant linkage to common types of migraine--migraine with or without aura--have been identified on four different chromosomes using a genome-wide screen approach. So far, only the locus on 4q has been replicated but no specific, disease-causing mutations have been described in these common forms of migraine. The best genetic evidence providing molecular insight into migraine still comes from the mutations detected in a rare Mendelian form of migraine with aura--familial hemiplegic migraine (FHM). In 50%-70% of FHM families, mutations in the calcium channel gene CACNA1A in chromosome 19p13 have been identified. In some families, mutations in the ATP1A2 gene encoding the alpha2 subunit of the Na+, K+-ATPase are associated with FHM, linked to 1q23. Here we discuss the current knowledge of the heritability of migraine and rare migraine variants as models for understanding the pathophysiology of common migraine and animal models that might contribute to understanding common forms of migraine.

Activation of 5-HT1B/1D receptor in the periaqueductal gray inhibits nociception

It is considered that the site of action of the abortive antimigraine compounds acting at serotonin, 5-HT(1B/1D,) receptors (triptans) is the trigeminovascular system. We tested whether there is a non-trigeminal site of action. The 5-HT(1B/1D) agonist, naratriptan, was microinjected into the ventrolateral periaqueductal gray (vlPAG), and activity in the trigeminal nucleus caudalis (TNC) was monitored. Recordings were made from 20 nociceptive neurons in the dorsal horn of the TNC that received convergent input from the dura mater and face. Responses of neurons to dural, facial cutaneous and corneal stimulation were studied before and after injection of naratriptan. Naratriptan decreased the excitability to electrical stimulation of the dura mater as the A-fiber response decreased by 24 +/- 4.1% (p < 0.001) and the C-fiber response decreased by 42 +/- 8.2% (p < 0.001). Spontaneous activity was decreased by 38 +/- 7.5% (p < 0.001). After injection, the mechanical thresholds of the dura mater increased from (n = 14, p < 0.01). Responses to stimulation of the face and cornea were not altered by injection of naratriptan. These results suggest that 5-HT(1B/1D) receptor activation in the vlPAG activates descending pain-modulating pathways that inhibit dural, but not facial and corneal nociceptive input. These findings have implications for the understanding of the action of triptans in migraine and cluster headache, suggesting that brain loci other than the trigeminal nucleus may play a role in the clinical action of triptans.

Voltage-dependent calcium channels are involved in neurogenic dural vasodilatation via a presynaptic transmitter release mechanism

Amissense mutation of the CACNA1A gene that encodes the alpha1A subunit of the voltage-dependent P/Q-type calcium channel has been discovered in patients suffering from familial hemiplegic migraine. This suggested that calcium channelopathies may be involved in migraine more broadly, and established the importance of genetic mechanisms in migraine. Channelopathies share many clinical characteristics with migraine, and thus exploring calcium channel functions in the trigeminovascular system may give insights into migraine pathophysiology. It is also known that drugs blocking the P/Q- and N-type calcium channels have been successful in other animal models of trigeminovascular activation and head pain. In the present study, we used intravital microscopy to examine the effects of specific calcium channel blockers on neurogenic dural vasodilatation and calcitonin gene-related peptide (CGRP)-induced dilation. The L-type voltage-dependent calcium channel blocker calciseptine significantly attenuated (20 microg kg(-1), n=7) the dilation brought about by electrical stimulation, but did not effect CGRP-induced dural dilation. The P/Q-type voltage-dependent calcium channel blocker omega-agatoxin-IVA (20 microg kg-1, n=7) significantly attenuated the dilation brought about by electrical stimulation, but did not effect CGRP-induced dural dilation. The N-type voltage-dependent calcium channel blocker omega-conotoxin-GVIA (20 microg kg(-1), n=8 and 40 microg kg(-1), n=7) significantly attenuated the dilation brought about by electrical stimulation, but did not effect CGRP-induced dural dilation. It is thought that the P/Q-, N- and L-type calcium channels all exist presynaptically on trigeminovascular neurons, and blockade of these channels prevents CGRP release, and, therefore, dural blood vessel dilation. These data suggest that the P/Q-, N- and L-type calcium channels may be involved in trigeminovascular nociception.

The trigeminocervical complex and migraine: current concepts and synthesis

Neurones in the trigeminocervical complex are the major relay neurones for nociceptive afferent input from the meninges and cervical structures; therefore, they are the neural substrates of head pain. This review highlights the importance of two basic mechanisms in headache physiology: convergence of nociceptive afferents and sensitization of trigeminocervical neurones. These physiologic findings have clinical correlates such as hypersensitivity and spread and referral of pain frequently seen in patients with primary headache, such as migraine. Special reference is made to the influence of structures from the upper cervical spine in generating and contributing to migraine headaches. The pathophysiology and functional relevance of these basic mechanisms to headaches is discussed in the context of recent experimental findings with regard to pain processing.

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

We investigated the occurrence of migraine without aura (MO) and migraine with typical aura (MA) amongst probands with familial hemiplegic migraine (FHM) and their first degree relatives in order to evaluate the relations between these syndromes. A total of 44 FHM probands and 240 first degree relatives were identified in the Danish population. The pattern of familial aggregation was assessed by population relative risk (PRR) calculations. Amongst FHM probands the PRR of MO was 1.5 (95% CI: 0.8-2.2), whereas the PRR of MA was 7.1 (95% CI: 5.0-9.2). Thus, compared with the general population, FHM probands had no increased risk of MO but a significantly increased risk of MA. A similar pattern was seen amongst their first degree relatives, who had no increased risk of MO, whereas the risk of MA was significantly increased; 7.6 times in FHM-affected first degree relatives and 2.4-times in non-FHM-affected first degree relatives. These results are contrary to a sharing of genetic mechanisms between FHM and MO. Furthermore, they suggest that the genetic abnormality causing FHM may also cause attacks with the symptomatology of MA.

Trigeminofacial reflexes in primary headaches

Nociceptive processing in trigeminal system is likely to undergo to significant changes in chronic pain disorders such as in primary headache. The electrophysiological testing of brainstem reflexes seems to offer a valuable adjunct to the clinical evaluation, providing direct evidence for central dysmodulation of sensory and pain neurotransmission, i.e. dishabituation pattern and reduced pain threshold. We review the contribution of trigeminofacial reflex studies in the light of those recent data supporting the view of a dysfunctional sensory processing in primary headache.

Pathophysiology, epidemiology, and impact of migraine

Despite a decade of progress, migraine headache remains prevalent, disabling, underdiagnosed, and undertreated in the United States. Migraine affects approximately 12% of the population, and the economic burden in terms of annual cost of labor lost to migraine disability is between $5.6 and $17.2 billion. The threshold for migraine may be genetically determined, although recent genetic and neurophysiologic studies point to migraine as possibly a channelopathy. Cerebral cortical and brain stem changes occur in migraine. Head pain and associated symptoms of migraine can be explained by activation of the trigeminal vascular system. Evidence has also been accumulated that suggests the release of nitric oxide is an important trigger mechanism. Introduction of the triptans has dramatically advanced acute migraine pharmacotherapy, and preventive therapy has greatly improved; however, public health initiatives may be needed to further advance diagnosis and treatment of this common and disabling disorder.