Genetic heterogeneity of familial hemiplegic migraine

Genetics of migraine: Delineation of contemporary understanding of the genetic underpinning of migraine

Migraine is a disabling episodic brain disorder with an increased familial relative risk, an increased concordance in monozygotic twins, and an estimated heritability of approximately 50%. Various genetic approaches have been applied to identify genetic factors conferring migraine risk. Initially, 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) are applied that test genetic variants, single-nucleotide polymorphisms (SNPs), in a hypothesis-free manner. To date, GWAS have identified ~40 genetic loci associated with migraine. New GWAS data, which are expected to come out soon, will reveal over 100 loci. Also, large-scale GWAS, which have appeared for many traits over the last decade, have enabled studying the overlap in genetic architecture between migraine and its comorbid disorders. Importantly, other genetic factors that cannot be identified by a GWAS approach also confer risk for migraine. First steps have been taken to determine the contribution of these mechanisms by investigating mitochondrial DNA and epigenetic mechanisms. In addition to typical epigenetic mechanisms, that is, DNA methylation and histone modifications, also RNA-based mechanisms regulating gene silencing and activation have recently gotten attention. Regardless, until now, most relevant genetic discoveries related to migraine still come from investigating monogenetic syndromes with migraine as a prominent part of the phenotype. Experimental studies on these syndromes have expanded our knowledge on the mechanisms underlying migraine pathophysiology. It can be envisaged that when all (epi)genetic and phenotypic data on the common and rare forms of migraine will be integrated, this will help to unravel the biological mechanisms for migraine, which will likely guide decision-making in clinical practice in the future.

An Update: Pathophysiology of Migraine

Migraine is the most common disabling primary headache globally. Attacks typically present with unilateral throbbing headache and associated symptoms including, nausea, multisensory hypersensitivity, and marked fatigue. In this article, the authors address the underlying neuroanatomical basis for migraine-related headache, associated symptomatology, and discuss key clinical and preclinical findings that indicate that migraine likely results from dysfunctional homeostatic mechanisms. Whereby, abnormal central nervous system responses to extrinsic and intrinsic cues may lead to increased attack susceptibility.

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.

A single-fibre EMG Study of Neuromuscular Transmission in Migraine Patients

It is known that mutations of CACNA1A, which encodes a neuronal P/Q Ca2+ channel, are present in patients with familial hemiplegic migraine, and possibly in other types of migraine as well. This calcium channel is also involved in neuromuscular transmission. To assess if the single-fibre EMG (SFEMG) method can demonstrate a neuromuscular transmission deficit in migraine, a group of 26 patients with different types of migraine and 20 healthy control subjects were studied. The migraine patients were divided into three groups: 8 patients with migraine without aura (MoA), 12 with migraine with aura excluding visual aura (MA) and 6 with visual aura (VA). A SFEMG of the voluntarily activated extensor digitorum communis muscle was performed. The SFEMG results were normal in the healthy controls and the MoA group (migraine without aura). Slight neuromuscular transmission disturbances were present in 6/12 (50%) of patients with MA and in 1/6 (17%) of patients with VA. We suggest that abnormal neuromuscular transmission detectable by SFEMG may reflect a genetically determined dysfunction of the P/Q Ca2+ channels in a subgroup of migraineurs with aura.

Genetics of migraine: an update

An important genetic component of migraine was systematically established by epidemiological studies in the 1990s. Over the past 15 years, significant progress has been made in unraveling the genetic basis and pathophysiological mechanisms of familial hemiplegic migraine, a rare and severe autosomal-dominant subtype of migraine with aura. Three different causative genes (CACNA1A, ATP1A2 and SCN1A), all of which are involved in cerebral ion translocation, have been identified. Functional studies and mouse models have shown that mutations in these genes, by different mechanisms, cause a disturbed cerebral glutamate homeostasis and, thus, increase susceptibility to cortical spreading depression, the likely correlate of migraine aura. More recently, genome-wide association studies have, for the first time, detected robust risk variants associated with the more common, genetically complex types of migraine, which has generated new perspectives for genetic research in migraine. This review summarizes the current knowledge about migraine genetics, with a focus on both familial hemiplegic migraine and recent results of genome-wide association studies.

A single-fibre electromyography study of neuromuscular transmission in patients with cluster headache

BACKGROUND AND PURPOSE

Mutations of CACNA1A, which encodes a neuronal P/Q Ca2+ channel, are present in patients with familial hemiplegic migraine, and possibly in other types of migraine as well. This calcium channel is also involved in neuromuscular transmission. In our previous study we confirmed that the single-fibre electromyography (SFEMG) method can demonstrate a neuromuscular transmission deficit in migraine with aura. The aim of our present study was to estimate the neurotransmitter dysfunction in cluster headache and to compare the results between patients with cluster headache and those with migraine with aura.

MATERIAL AND METHODS

We selected 6 patients with cluster headache and 6 patients with migraine with typical aura. SFEMG of the voluntarily activated extensor digitorum communis muscle was performed.

RESULTS

The SFEMG results were in the normal range in the cluster headache group and in the healthy controls. Slight neuromuscular transmission disturbances were present in patients with migraine with aura.

CONCLUSIONS

The abnormal neuromuscular transmission detectable by SFEMG may reflect a genetically determined dysfunction of the P/Q Ca2+ channels in a group of migraineurs with aura. Conversely, absence of neuromuscular abnormalities in cluster headache patients could be explained by different aetiology not resulting in channelopathy. Single-fibre electromyography could be a helpful tool in clinically questionable cases in differentiating between cluster headache and migraine with aura.

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.

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.

Use of antiepileptic drugs for hyperkinetic movement disorders

Many studies investigated the use of antiepileptic drugs (AEDs) in several neurological diseases other than epilepsy. These neurological disorders, usually, involve neuronal excitability through the modulating of ion channels, receptors and intracellular signaling pathways, and are the targets of the AEDs. This article provides a review of the clinical efficacy of both conventional and newer AEDs in hyperkinetic movement disorders. Some of these indications for AEDs have been established, while others are under investigation. The modulation of GABAergic transmission may explain the neuronal hyper-excitability that underlies some forms of hyperkinetic movement disorders. So, AEDs able to increase GABAergic neurotransmission may play a role in hyperkinetic movement disorders treatment. Therefore, AEDs could represent a useful therapeutic option in the management of hyperkinetic movement disorders where the available treatments are ineffective.

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 high-density association screen of 155 ion transport genes for involvement with common migraine

The clinical overlap between monogenic Familial Hemiplegic Migraine (FHM) and common migraine subtypes, and the fact that all three FHM genes are involved in the transport of ions, suggest that ion transport genes may underlie susceptibility to common forms of migraine. To test this leading hypothesis, we examined common variation in 155 ion transport genes using 5257 single nucleotide polymorphisms (SNPs) in a Finnish sample of 841 unrelated migraine with aura cases and 884 unrelated non-migraine controls. The top signals were then tested for replication in four independent migraine case-control samples from the Netherlands, Germany and Australia, totalling 2835 unrelated migraine cases and 2740 unrelated controls. SNPs within 12 genes (KCNB2, KCNQ3, CLIC5, ATP2C2, CACNA1E, CACNB2, KCNE2, KCNK12, KCNK2, KCNS3, SCN5A and SCN9A) with promising nominal association (0.00041 < P < 0.005) in the Finnish sample were selected for replication. Although no variant remained significant after adjusting for multiple testing nor produced consistent evidence for association across all cohorts, a significant epistatic interaction between KCNB2 SNP rs1431656 (chromosome 8q13.3) and CACNB2 SNP rs7076100 (chromosome 10p12.33) (pointwise P = 0.00002; global P = 0.02) was observed in the Finnish case-control sample. We conclude that common variants of moderate effect size in ion transport genes do not play a major role in susceptibility to common migraine within these European populations, although there is some evidence for epistatic interaction between potassium and calcium channel genes, KCNB2 and CACNB2. Multiple rare variants or trans-regulatory elements of these genes are not ruled out.

A pharmacogenomic evaluation of migraine therapy

Migraine is a common idiopathic primary headache disorder with significant mental, physical and social health implications. Accompanying an intense unilateral pulsating head pain other characteristic migraine symptoms include nausea, emesis, phonophobia, photophobia and in approximately 20-30% of migraine cases, neurologic disturbances associated with the aura phase. Although selective serotonin (5-HT) receptor agonists (i.e., 5-HT(1B/1D)) are successful in alleviating migrainous symptoms in < or = 70% of known sufferers, for the remaining 30%, additional migraine abortive medications remain unsuccessful, not tested or yet to be identified. Genetic characterization of the migrainous disorder is making steady progress with an increasing number of genomic susceptibility loci now identified on chromosomes 1q, 4q, 5q, 6p, 11q, 14q, 15q, 17p, 18q, 19p and Xq. The 4q, 5q, 17p and 18q loci involve endophenotypic susceptibility regions for various migrainous symptoms. In an effort to develop individualized pharmacotherapeutics, the identification of these migraine endophenotypic loci may well be the catalyst needed to aid in this goal. In this review the authors discuss the present treatment of migraine, known genomic susceptibility regions and results from migraine (genetic) association studies. The authors also discuss pharmacogenomic considerations for more individualized migraine prophylactic treatments.

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.

Association of progesterone receptor with migraine-associated vertigo

While migraine has been demonstrated to be familial and have genetic contributions, genome-wide linkage analyses and candidate gene studies have highlighted that migraine is genetically complex. Despite substantial efforts, no consistent replication of linkage or association has been reported for common migraine syndromes. Among the candidate genes tested for association with migraine by several groups were female sex hormone genes based on the observation of a much higher incidence of migraine in females. Migraine-associated vertigo (MAV) is a migraine syndrome also much more common in females than males. Because MAV is less common in the general population than migraine or migraine with aura, it may be a better migraine syndrome to detect susceptibility alleles. In this study, we tested the association of two female hormonal genes, progesterone receptor (PGR) and estrogen receptor (ESR1), which were previously reported to be associated with migraine in women. We typed 150 MAV subjects and 145 genomic matched control subjects. One SNP (rs1042838) within PGR, which is in high linkage disequilibrium with the functional PROGINS variant, was significantly associated with MAV (p = 0.0007). Two SNPs (rs2228480 and rs1801132) within ESR1 demonstrated no significant association. No synergistic effect between ESR1 variants and PGR variants was identified.

Migraine and stroke - why do we talk about it?

Data from observational studies suggest that migraine may be a risk factor for stroke. Furthermore, a significant association between migraine and ischemic stroke (IS) has been demonstrated in population and case-control studies. The risk of IS appears to be higher for migraine with aura than for migraine without aura. The pathogenesis is not known but several studies report some common biochemical mechanisms in the two diseases. Meta-analysis also demonstrates that subjects with migraine are at higher risk of showing white matter abnormalities on magnetic resonance images than are those without migraine.

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.

Migraine: Current concepts and emerging therapies

Migraine is a recurrent incapacitating neurovascular disorder characterized by attacks of debilitating pain associated with photophobia, phonophobia, nausea and vomiting. Migraine affects a substantial fraction of world population and is a major cause of disability in the work place. Though the pathophysiology of migraine is still unclear three major theories proposed with regard to the mechanisms of migraine are vascular (due to cerebral vasodilatation), neurological (abnormal neurological firing which causes the spreading depression and migraine) and neurogenic dural inflammation (release of inflammatory neuropeptides). The modern understanding of the pathogenesis of migraine is based on the concept that it is a neurovascular disorder. The drugs used in the treatment of migraine either abolish the acute migraine headache or aim its prevention. The last decade has witnessed the advent of Sumatriptan and the 'triptan' class of 5-HT1B/1D receptor agonists which have well established efficacy in treating migraine. Currently prophylactic treatments for migraine include calcium channel blockers, 5-HT2 receptor antagonists, beta adrenoceptor blockers and gamma-amino butyric acid (GABA) agonists. Unfortunately, many of these treatments are non specific and not always effective. Despite such progress, in view of the complexity of the etiology of migraine, it still remains undiagnosed and available therapies are underused. In this article, the diverse pieces of evidence that have linked the different theories of migraine with its pathophysiology are reviewed. Furthermore, the present therapeutic targets and futuristic approaches for the acute and prophylactic treatment of migraine, with a special emphasis to calcitonin gene-related peptide, are critically evaluated.

Migraine Pathophysiology

A combination of basic science and human physiology, particularly functional neuroimaging, has radically altered our understanding of migraine with a focus on brain mechanisms for this common and disabling disorder. Genetic studies have begun to provide plausible targets for the basic molecular defect in terms of ion channels, albeit thus far in the rare condition of familial hemiplegic migraine (FHM). Migraine pathophysiology involves the trigeminovascular system and central nervous system modulation of the pain-producing structures of the cranium. The degree to which head pain results from the activation of the nociceptors of pain-producing intracranial structures, or to the facilitation or lack of inhibition of afferent signals, is not clear at this time. An understanding of the pain mechanism is likely to provide insights into the mechanisms underlying the more generalized sensory dysfunction that is so typical of migraine.

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.

A Cacna1a knockin migraine mouse model with increased susceptibility to cortical spreading depression

Migraine is a common, disabling, multifactorial, episodic neurovascular disorder of unknown etiology. Familial hemiplegic migraine type 1 (FHM-1) is a Mendelian subtype of migraine with aura that is caused by missense mutations in the CACNA1A gene that encodes the alpha(1) subunit of neuronal Ca(v)2.1 Ca(2+) channels. We generated a knockin mouse model carrying the human pure FHM-1 R192Q mutation and found multiple gain-of-function effects. These include increased Ca(v)2.1 current density in cerebellar neurons, enhanced neurotransmission at the neuromuscular junction, and, in the intact animal, a reduced threshold and increased velocity of cortical spreading depression (CSD; the likely mechanism for the migraine aura). Our data show that the increased susceptibility for CSD and aura in migraine may be due to cortical hyperexcitability. The R192Q FHM-1 mouse is a promising animal model to study migraine mechanisms and treatments.

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.

Latent class and genetic analysis does not support migraine with aura and migraine without aura as separate entities

Latent class and genetic analyses were used to identify subgroups of migraine sufferers in a community sample of 6,265 Australian twins (55% female) aged 25-36 who had completed an interview based on International Headache Society (IHS) criteria. Consistent with prevalence rates from other population-based studies, 703 (20%) female and 250 (9%) male twins satisfied the IHS criteria for migraine without aura (MO), and of these, 432 (13%) female and 166 (6%) male twins satisfied the criteria for migraine with aura (MA) as indicated by visual symptoms. Latent class analysis (LCA) of IHS symptoms identified three major symptomatic classes, representing 1) a mild form of recurrent nonmigrainous headache, 2) a moderately severe form of migraine, typically without visual aura symptoms (although 40% of individuals in this class were positive for aura), and 3) a severe form of migraine typically with visual aura symptoms (although 24% of individuals were negative for aura). Using the LCA classification, many more individuals were considered affected to some degree than when using IHS criteria (35% vs. 13%). Furthermore, genetic model fitting indicated a greater genetic contribution to migraine using the LCA classification (heritability, h(2)=0.40; 95% CI, 0.29-0.46) compared with the IHS classification (h(2)=0.36; 95% CI, 0.22-0.42). Exploratory latent class modeling, fitting up to 10 classes, did not identify classes corresponding to either the IHS MO or MA classification. Our data indicate the existence of a continuum of severity, with MA more severe but not etiologically distinct from MO. In searching for predisposing genes, we should therefore expect to find some genes that may underlie all major recurrent headache subtypes, with modifying genetic or environmental factors that may lead to differential expression of the liability for migraine.

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.

Hereditary porencephaly: clinical and MRI findings in two Dutch families

Familial porencephaly is a rare disorder causing motor impairment, hemiplegia, mental retardation and epilepsy in variable degrees. Two families with porencephaly and apparently dominant inheritance are reported. Brain MRI findings are reviewed and described in seven affected individuals. Most patients also show white matter abnormalities in the cerebral hemisphere, also contralateral to the cystic lesion. In the first family an obligate carrier was identified who did not have a cystic lesion but clear abnormalities of the white matter. Although a predisposition for thrombophilia has previously been reported, we did not observe any genetic, environmental or epigenetic predisposition for the porencephaly. The lesions are most compatible with a deep venous thrombosis/ischemic event occurring in a late stage of pregnancy, not necessarily aggravated by perinatal asphyxia.

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.

The genetics of migraine: implication for treatment approaches

Migraine is a paroxysmal neurological disorder affecting up to 12% of males and 24% of females in the general population, demonstrated to have a strong, but complex, genetic component. Genetic investigation of migraine bears great promise in providing new targets for drug development and optimization of individual specific therapy. Better, preferably prophylactic, treatment of migraine patients is desired because the presently used drugs are not effective in all patients, allow recurrence of the headache in a high percentage of patients and sometimes have severe adverse side effects. With the recent identification of the brain-specific P/Q-type calcium channel gene CACNA1A in the pathogenesis of migraine, the first step has been taken to identify primary biochemical pathways leading to migraine. Here, we summarize the current knowledge about the genetics of migraine and focus on the implication for treatment approaches.

Migraine genetics

The genetics of migraine is a fascinating and 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 in approximately 75% of the families. The finding of mutations in an ionchannel subunit defines migraine as a channelopathy (eg, epilepsy). The genetics of the more frequent variants, migraine with and without aura, is more complex. Several loci have been studied in families and case-control studies, but need to be confirmed.

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.

Familial hemiplegic migraine type 2 is linked to 0.9Mb region on chromosome 1q23

Familial hemiplegic migraine (FHM) is a rare autosomal dominant disorder characterized by episodes of transient hemiparesis followed by headache. Two chromosomal loci are associated to FHM: FHM1 on chromosome 19 and FHM2 on chromosome 1q21-23. Mutations of the alpha-1A subunit of the voltage gated calcium channel (CACNA1A) are responsible for FHM1. FHM2 critical region spans 28 cM, hence hampering the identification of the responsible gene. Here, we report the FHM2 locus refining by linkage analysis on two large Italian families affected by pure FHM. The new critical region covers a small area of 0.9Mb in 1q23 and renders feasible a positional candidate approach. By mutation analysis, we excluded the calsequestrin and two potassium channel genes mapping within the narrowed FHM2 locus.

The genetics of migraine

The search for genes involved in the pathophysiology of migraine poses major difficulties. First, there is no objective diagnostic method to assess the status of the individuals studied. Second, migraine is a polygenic multifactorial disorder. Familial hemiplegic migraine (FHM) is the only known autosomal dominant subtype of migraine. In half the families with FHM who have been studied, there are mutations in the calcium-channel gene CACNA1A, located on chromosome 19. In other families, a locus has been mapped on chromosome 1. The role of these loci in typical migraine is still unknown. A susceptibility locus for migraine with aura has been located on chromosome 19 (but is distinct from CACNA1A) and a genome-wide linkage analysis has mapped a susceptibility locus on chromosome 4. Another locus for migraine may be on the X chromosome. Finally, many positive association studies have been published, but few have been replicated.

Migraine without aura and migraine with aura are distinct disorders. A population-based twin survey

OBJECTIVE

To investigate the co-occurrence of migraine without aura (MWOA) and migraine with aura (MWA) in a population-based twin survey.

BACKGROUND

Migraine without aura and MWA are multifactorial disorders. If MWOA and MWA share common genes, co-occurrence should be observed more frequently than expected, ie, the product of the prevalence in the general population.

MATERIAL AND METHODS

The study population included all living Danish monozygotic (MZ) and same-gender dizygotic (DZ) twin pairs born between 1953 and 1960: 5360 twins (2026 MZ, 3334 DZ). The sample included 2840 men and 2520 women. All received a posted questionnaire, and those with possible migraine were interviewed via telephone by trained physicians (V.U. or M.G.). Twins who did not respond to the questionnaire and who had a co-twin with possible migraine were contacted by telephone. The questionnaire response rate was 87% (4660 of 5360), and the telephone interview was participated in by 90% (2035 of 2272). The physician interviewers were unaware of questionnaire answers, zygosity, and the clinical diagnosis of the co-twin. The criteria of the International Headache Society were used to establish a diagnosis of migraine.

RESULTS

Lifetime prevalence in the twin sample: 7% of men and 19% of women had MWOA, while 7% of men and 8% of women had MWA. Lifetime prevalence of MWA in twin pairs with MWOA: MZ men, 2% (1 of 47); MZ women, 6% (5 of 90); DZ men, 9% (7 of 75); and DZ women, 10% (19 of 182). Lifetime prevalence of MWOA in twin pairs with MWA: MZ men, 3% (1 of 33); MZ women, 5% (3 of 58); DZ men, 9% (4 of 44); and DZ women, 13% (10 of 76). The observed and the expected numbers of twins with co-occurrence of MWOA and MWA based on the prevalence in the general population were not significantly different in either men or women (men, P=.1 and women, P=.5).

CONCLUSION

The results strongly suggest that MWOA and MWA are distinct disorders, and identification of common genes for MWOA and MWA, thus, should not be expected to result from future genetic research.

Hemiplegic migraine with prolonged symptoms: case report

Hemiplegic migraine is defined by the occurrence of migraine during attacks of unilateral weakness. Neurologic symptoms last for 15 to 60 minutes in most cases. Attacks usually start in childhood, adolescence, or early adulthood. Diagnosis may be delayed if there is no relevant family history. A 16-year-old girl who was diagnosed with hemiplegic migraine presenting with prolonged left hemiparesis is reported. The importance of this case is that the pediatrician will also consider migraine in the differential diagnosis of a child presenting with hemiparesis even if there is no previous headache and family history.

Familial hemiplegic migraine: a ion channel disorder

At present, little information is available on the genetics of common migraines, most likely to be considered a multifactorial disease. Recently, the CACNA1A gene encoding the brain-specific P/Q type calcium channel alpha(1) subunit, has been cloned and mutations in this gene, located on chromosome 19p13, have been shown to be involved in familial hemiplegic migraine (FHM), a rare autosomal dominantly inherited subtype of migraine with aura. Being part of the migraine spectrum, FHM represents a good model to study the genetics of more common forms of migraine. Different classes of mutations within the CACNA1A gene have been associated with different diseases, thus identifying a new member among 'channelopathies'. Variable clinical expression and genetic heterogeneity of FHM will be discussed.

Idiopathic epilepsy and paroxysmal dyskinesia

Although some motor manifestations of epilepsy and of paroxysmal dyskinesia may be difficult to differentiate clinically, the current understanding is that the two disorders are clinically distinct. However, there are several recent reports of families in which different individuals had either disorder or both manifestations, with age-related expression. Co-occurrence makes it likely that a common, genetically determined, pathophysiologic abnormality is variably expressed in the cerebral cortex and in basal ganglia. A rather homogeneous syndrome of autosomal dominant infantile convulsions and paroxysmal (dystonic) choreoathetosis (ICCA) was described in six families from France, China and Japan. Linkage analysis in the French and Chinese families allowed the mapping of the disease gene in a 10-cM interval within the pericentromeric region of chromosome 16. An Italian pedigree in which three members in the same generation were affected by rolandic epilepsy, paroxysmal exercise-induced dystonia (PED), and writer's cramp was subsequently reported. Linkage analysis showed a common homozygous haplotype in a critical region spanning 6 cM and entirely included within the ICCA critical region. Clinical analogies and linkage findings suggest that the same gene could be responsible for rolandic epilepsy, PED, writer's cramp (WC), and ICCA, with specific mutations accounting for each of these mendelian disorders. Evidence for a major gene or a cluster of genes for epilepsy and paroxysmal dyskinesia to the pericentromeric region of chromosome 16 is reinforced by the recent linkage of a family with autosomal dominant paroxysmal dyskinesia to a critical region partially overlapping with ICCA and contiguous to the RE-PED-WC regions. Additional autosomal dominant pedigrees are on record, from Australia and Italy, in which epilepsy was variably associated with paroxysmal kinesigenic or exercise-induced dystonia. Ion channel genes are potentially interesting candidates for syndromes featuring both these paroxysmal neurologic disorders. Increased awareness of their possible co-occurrence will certainly increase the number of observations in the next few years.

The clinical spectrum of familial hemiplegic migraine associated with mutations in a neuronal calcium channel

BACKGROUND

Familial hemiplegic migraine, an autosomal dominant disorder characterized by attacks of transient hemiparesis followed by a migraine headache, is classically divided into pure familial hemiplegic migraine (affecting 80 percent of families) and familial hemiplegic migraine with permanent cerebellar signs (affecting 20 percent of families). Mutations in CACNA1A, which encodes a neuronal calcium channel, are present in 50 percent of families with hemiplegic migraine, including all those with cerebellar signs. We studied the various clinical manifestations associated with mutations in CACNA1A in families with hemiplegic migraine with and without cerebellar signs.

METHODS

CACNA1A was analyzed and nine mutations were detected in 15 of 16 probands of families affected by hemiplegic migraine and cerebellar signs, in 2 of 3 subjects with sporadic hemiplegic migraine and cerebellar signs, and in 4 of 12 probands of families affected by pure hemiplegic migraine. Genotyping of probands and relatives identified a total of 117 subjects with mutations whose clinical manifestations were assessed in detail.

RESULTS

Eighty-nine percent of the subjects with mutations had attacks of hemiplegic migraine. One third had severe attacks with coma, prolonged hemiplegia, or both, with full recovery. All nine mutations, including five newly identified ones, were missense mutations. Six mutations were associated with hemiplegic migraine and cerebellar signs, and 83 percent of the subjects with these six mutations had nystagmus, ataxia, or both. Three mutations were associated with pure hemiplegic migraine.

CONCLUSIONS

Hemiplegic migraine in subjects with mutations in CACNA1A has a broad clinical spectrum. This clinical variability is partially associated with the various types of mutations.

Ion channel diseases of the central nervous system

In the last decade, advances in molecular genetics and cellular electrophysiology have increased our understanding of ion channel function. A number of diseases termed "channelopathies" have been discovered that are caused by ion channel dysfunction. Channelopathies can be caused by autoimmune, iatrogenic, toxic or genetic mechanisms. Mutations in genes encoding ion channel proteins that disrupt channel function are now the most commonly identified cause of channelopathies, perhaps because gene disruption is readily detected by the methods of molecular genetics. Ion channels are abundant in the central nervous system (CNS), but CNS channelopathies are rare; however, they overlap with some important neurological disorders, such as epilepsy, ataxia, migraine, schizophrenia, Alzheimer's disease and other neurodegenerative diseases. It is possible that more CNS channelopathies will be discovered when additional ion channels are characterized and the complex mechanisms of brain function are better understood. At present, increased knowledge of the identity, structure and function of ion channels is facilitating diagnosis and treatment of many channelopathies.

Recent development in paediatric headache

Headache is one of the most common disorders that occurs during the early, developmental years of life. The present review critically discusses the most recently published reports concerning headache with onset in youngsters, delineating the current status of research in the various fields and outlining areas that require further investigation. Age-related characteristics need to be taken into account with considering the aetiology, diagnosis and treatment of juvenile headache.

The impact of pharmacogenetics for migraine

Migraine is a paroxysmal neurological disorder affecting up to 12% of males and 24% of females in the general population. As migraine has been demonstrated to have a strong, but complex, genetic component, pharmacogenetics bears great promise in providing new targets for drug development and optimization of individual specific therapy. Better, preferably prophylactic, treatment of migraine patients is desired because the drugs now used are not effective in all patients, allow recurrence of the headache in a high percentage of patients and sometimes have severe adverse side-effects. With the recent identification of the brain-specific P/Q-type Ca(2+)channel gene CACNA1A as a pivotal player in the pathogenesis of migraine, the first step has been taken to identify primary biochemical pathways leading to migraine. The work on migraine can also have implications for the increasing number of additional neurological episodic disorders having the common denominator of channelopathy.

Molecular genetics of migraine headaches: a review

Following the recent discovery of neural calcium channel mutations in familial hemiplegic migraine, genetic linkage and association studies have been performed world-wide in an effort to unveil the genetic basis of the more common types of migraine too. Mutations in neural calcium channels, mitochondrial DNA, serotonin receptors and transporter, dopamine receptors and genetic prothrombotic risk factors have been especially investigated and are discussed here. No unambiguous conclusions have, however, been reached. FHM remains an isolated success story in the quest for the genetic basis of migraine.

Coincidence of familial hemiplegic migraine and hemicrania continua? A case report

A case is presented of a 39-year-old woman with a history of simultaneous Familial hemiplegic migraine (FHM) and hemicrania continua (HC). The family history of the patient revealed different types of migraine and cyclic syndromes in childhood in four generations. The possible links between FHM and HC are discussed. The pedigree gives further evidence that cyclic syndromes in childhood belong to the spectrum of migraine.