Single-nucleotide polymorphism alleles in the insulin receptor gene are associated with typical migraine

The Dawn and Advancement of the Knowledge of the Genetics of Migraine

Background: Migraine is a prevalent episodic brain disorder known for recurrent attacks of unilateral headaches, accompanied by complaints of photophobia, phonophobia, nausea, and vomiting. Two main categories of migraine are migraine with aura (MA) and migraine without aura (MO). Main body: Early twin and population studies have shown a genetic basis for these disorders, and efforts have been invested since to discern the genes involved. Many techniques, including candidate-gene association studies, loci linkage studies, genome-wide association, and transcription studies, have been used for this goal. As a result, several genes were pinned with concurrent and conflicting data among studies. It is important to understand the evolution of techniques and their findings. Conclusions: This review provides a chronological understanding of the different techniques used from the dawn of migraine genetic investigations and the genes linked with the migraine subtypes.

Associations of type 2 diabetes and the risk of migraine in Chinese populations

AIM

We aimed to explore the relationship between type 2 diabetes mellitus (T2DM) and the incidence rate of migraine in a Chinese population, and analyze the clinical characteristics of migraine patients with T2DM.

METHODS

Data on the study cohort of 9873 individuals were obtained from the China Health and Retirement Longitudinal Study (CHARLS). The incidence rate of migraine from 2015 to 2018 was assessed. The Cox proportional hazards model was used to estimate hazard ratios (HRs) and their 95% confidence intervals (CIs) for the relationship between T2DM and the incidence of migraine. In addition, a cross-sectional study including 168 migraine patients was conducted in Xiamen, China. Migraine patients were grouped according to their T2DM status. Multivariable linear regression models were used to estimate βs and their 95% CIs for the relationship between migraine characteristics and T2DM.

RESULTS

The cumulative incidence rate of migraine from 2015 to 2018 in the T2DM group and control group was 7.26% [6.04%.8.65%] and 8.91% [8.27%.9.58%], respectively. The risk of migraine in patients with T2DM was reduced by 21% (HR 0.79 [0.65;0.95]) compared to patients with no T2DM after adjustment for confounders. The cross-sectional study showed that the presence of T2DM significantly reduced migraine frequency and relieved migraine intensity.

CONCLUSION

This was the first study to validate that T2DM reduced the risk of migraine in a Chinese population cohort. Patients with migraine and T2DM may experience significant relief from their headache symptoms. Carrying out relevant mechanistic research may help to identify new targets for migraine treatment and contribute to further understanding the impact of T2DM or related metabolic disorders on an individual's health.

Current Update on Categorization of Migraine Subtypes on the Basis of Genetic Variation: a Systematic Review

Migraine is a complex neurovascular disorder that is characterized by severe behavioral, sensory, visual, and/or auditory symptoms. It has been labeled as one of the ten most disabling medical illnesses in the world by the World Health Organization (Aagaard et al Sci Transl Med 6(237):237ra65, 2014). According to a recent report by the American Migraine Foundation (Shoulson et al Ann Neurol 25(3):252-9, 1989), around 148 million people in the world currently suffer from migraine. On the basis of presence of aura, migraine is classified into two major subtypes: migraine with aura (Aagaard et al Sci Transl Med 6(237):237ra65, 2014) and migraine without aura. (Aagaard K et al Sci Transl Med 6(237):237ra65, 2014) Many complex genetic mechanisms have been proposed in the pathophysiology of migraine but specific pathways associated with the different subtypes of migraine have not yet been explored. Various approaches including candidate gene association studies (CGAS) and genome-wide association studies (Fan et al Headache: J Head Face Pain 54(4):709-715, 2014). have identified the genetic markers associated with migraine and its subtypes. Several single nucleotide polymorphisms (Kaur et al Egyp J Neurol, Psychiatry Neurosurg 55(1):1-7, 2019) within genes involved in ion homeostasis, solute transport, synaptic transmission, cortical excitability, and vascular function have been associated with the disorder. Currently, the diagnosis of migraine is majorly behavioral with no focus on the genetic markers and thereby the therapeutic intervention specific to subtypes. Therefore, there is a need to explore genetic variants significantly associated with MA and MO as susceptibility markers in the diagnosis and targets for therapeutic interventions in the specific subtypes of migraine. Although the proper characterization of pathways based on different subtypes is yet to be studied, this review aims to make a first attempt to compile the information available on various genetic variants and the molecular mechanisms involved with the development of MA and MO. An attempt has also been made to suggest novel candidate genes based on their function to be explored by future research.

Alterations in metabolic flux in migraine and the translational relevance

BACKGROUND

Migraine is a highly prevalent disorder with significant economical and personal burden. Despite the development of effective therapeutics, the causes which precipitate migraine attacks remain elusive. Clinical studies have highlighted altered metabolic flux and mitochondrial function in patients. In vivo animal experiments can allude to the metabolic mechanisms which may underlie migraine susceptibility. Understanding the translational relevance of these studies are important to identifying triggers, biomarkers and therapeutic targets in migraine.

MAIN BODY

Functional imaging studies have suggested that migraineurs feature metabolic syndrome, exhibiting hallmark features including upregulated oxidative phosphorylation yet depleted available free energy. Glucose hypometabolism is also evident in migraine patients and can lead to altered neuronal hyperexcitability such as the incidence of cortical spreading depression (CSD). The association between obesity and increased risk, frequency and worse prognosis of migraine also highlights lipid dysregulation in migraine pathology. Calcitonin gene related peptide (CGRP) has demonstrated an important role in sensitisation and nociception in headache, however its role in metabolic regulation in connection with migraine has not been thoroughly explored. Whether impaired metabolic function leads to increased release of peptides such as CGRP or excessive nociception leads to altered flux is yet unknown.

CONCLUSION

Migraine susceptibility may be underpinned by impaired metabolism resulting in depleted energy stores and altered neuronal function. This review discusses both clinical and in vivo studies which provide evidence of altered metabolic flux which contribute toward pathophysiology. It also reviews the translational relevance of animal studies in identifying targets of biomarker or therapeutic development.

Headaches and obesity

Obesity and headache disorders are two very common conditions in the general population that have been increasing in incidence over the last decades. Recent studies have shown a significant relationship between obesity and headaches, particularly migraine, with an important role in whether the disease is chronic. On the other hand, no such association was found with tension-type headaches. Studies showing an overlapping of hunger-control pathways and those involved in the pathophysiology of migraine may justify the close association between obesity and migraine. Moreover, a secondary headache for which obesity is a strong risk factor is idiopathic Intracranial Hypertension (pseudotumor cerebri), with several studies showing the impact of weight reduction/bariatric surgery in the treatment of the disease. In conclusion, since obesity is a modifiable risk factor, it is important for physicians treating patients with headaches, and particularly migraine, to be aware of the association between these two disorders.

Glucose-Related Traits and Risk of Migraine—A Potential Mechanism and Treatment Consideration

Migraine and glucose-related (glycaemic) traits (fasting glucose, fasting insulin, and type 2 diabetes) are common and complex comorbid disorders that cause major economic and social burdens on patients and their families. Studies on the relationship between migraine and glucose-related traits have yielded inconsistent results. The purpose of this review is to synthesise and discuss the information from the available literature on the relationship between fasting glucose, fasting insulin, and type 2 diabetes (T2D) with migraine. Publications on migraine and fasting glucose, migraine and fasting insulin, and migraine and T2D were identified from a PubMed and Google Scholar database search and reviewed for this article. Multiple publications have suggested that the comorbidity of migraine and glucose-related traits may have a similar complex pathogenic mechanism, including impaired glucose homeostasis, insulin resistance, reduced cerebrovascular reactivity, abnormal brain metabolism, shared genetic factors, neurotransmitters, and sex hormones. Furthermore, several studies have found a bi-directional link between migraine with insulin resistance and T2D. There is strong evidence for a biological association between migraine headache and glucose-related traits, and burgeoning evidence for shared genetic influences. Therefore, genetic research into these comorbid traits has the potential to identify new biomarkers and therapeutic targets and provide biological insight into their relationships. We encourage healthcare professionals to consider the co-occurrence of migraine with glucose-related traits in the evaluation and treatment of their patients.

Insulin sensitizes neural and vascular TRPV1 receptors in the trigeminovascular system

Background

Clinical observations suggest that hyperinsulinemia and insulin resistance can be associated with migraine headache. In the present study we examined the effect of insulin on transient receptor potential vanilloid 1 (TRPV1) receptor-dependent meningeal nociceptor functions in rats.

Methods

The effects of insulin on the TRPV1 receptor stimulation-induced release of calcitonin gene related peptide (CGRP) from trigeminal afferents and changes in meningeal blood flow were studied. Colocalization of the insulin receptor, the TRPV1 receptor and CGRP was also analyzed in trigeminal ganglion neurons.

Results

Insulin induced release of CGRP from meningeal afferents and consequent increases in dural blood flow through the activation of TRPV1 receptors of trigeminal afferents. Insulin sensitized both neural and vascular TRPV1 receptors making them more susceptible to the receptor agonist capsaicin. Immunohistochemistry revealed colocalization of the insulin receptor with the TRPV1 receptor and CGRP in a significant proportion of trigeminal ganglion neurons.

Conclusions

Insulin may activate or sensitize meningeal nociceptors that may lead to enhanced headache susceptibility in persons with increased plasma insulin concentration.

Was it something I ate? Understanding the bidirectional interaction of migraine and appetite neural circuits

Migraine attacks can involve changes of appetite: while fasting or skipping meals are often reported triggers in susceptible individuals, hunger or food craving are reported in the premonitory phase. Over the last decade, there has been a growing interest and recognition of the importance of studying these overlapping fields of neuroscience, which has led to novel findings. The data suggest additional studies are needed to unravel key neurobiological mechanisms underlying the bidirectional interaction between migraine and appetite. Herein, we review information about the metabolic migraine phenotype and explore migraine therapeutic targets that have a strong input on appetite neuronal circuits, including the calcitonin gene-related peptide (CGRP), the pituitary adenylate cyclase-activating polypeptide (PACAP) and the orexins. Furthermore, we focus on potential therapeutic peptide targets that are involved in regulation of feeding and play a role in migraine pathophysiology, such as neuropeptide Y, insulin, glucagon and leptin. We then examine the orexigenic - anorexigenic circuit feedback loop and explore glucose metabolism disturbances. Additionally, it is proposed a different perspective on the most reported feeding-related trigger - skipping meals - as well as a link between contrasting feeding behaviors (skipping meals vs food craving). Our review aims to increase awareness of migraine through the lens of appetite neurobiology in order to improve our understanding of the earlier phase of migraine, encourage better studies and cross-disciplinary collaborations, and provide novel migraine-specific therapeutic opportunities.

The Interrelation Between Chronic Headache, Cognitive Scores, and MRI Markers Among Stroke Survivors

BACKGROUND

Migraine is known to mildly increase the risk for ischemic stroke and is associated with vascular MRI markers. However, the potential effect of chronic headache (CH) on stroke outcomes has not been studied.

OBJECTIVE

We aimed to assess the interrelation between CH and post-stroke cognitive impairment.

METHODS

Data from 455 patients with a first ever stroke from the TABASCO study was available. All patients underwent 3T brain MRI, blood analysis, and a serial cognitive assessment at baseline and 6, 12, and 24 months after.

RESULTS

Eighty-five (18.7%) patients reported suffering from CH, of whom 53 (62.4%) reported symptoms of photophobia or nausea, and 34 (40%) reported an aura. CH was associated with female sex, lower prevalence of T2DM (p < 0.001), and lower HbA1C levels (p < 0.001). Multiple regression analysis, controlling for age, sex, education, vascular risk factors, and the presence of acute lesions in MRI, revealed that CH was an independent predictor of better cognitive scores 6, 12, and 24 months post-stroke (p = 0.015, p = 0.01, and p = 0.012, respectively). Stroke patients suffering from CH had also higher normalized gray, white matter, and thalamus volumes, and better white matter microstructural integrity (p < 0.001, p = 0.037, p < 0.001, p = 0.008, respectively)Conclusion:In this study, CH was consistently associated with better long term cognitive scores among post stroke subjects. These surprising findings may partially arise from the higher prevalence of T2DM among subjects without CH, that may represent the existence of chronic cerebrovascular disease, and may reflect mechanisms involving glucose metabolism.

A systematic literature review of observational studies of the bilateral association between diabetes and migraine

BACKGROUND AND AIM

To conduct a systematic literature review and synthesize data from all epidemiological studies investigating the association between diabetes and migraine in adults.

METHOD AND MATERIAL

Electronic databases, including Web of Science, PubMed and Scopus in addition to Google Scholar search engine were systematically searched up to Jun 2020 to identify studies reporting the diabetes-migraine association.

RESULTS

A total of 15 studies were selected which were published from 2012 to 2019. Five out of 15 studies assessed the presence of migraine in diabetic subjects, while nine studies assessed the presence of diabetes in migraine subjects. The cohort study reported a hazard ratio for diabetes of 1.06 (95% confidence interval (CI): 0.91-1.24) for women with migraine with aura, 1.01 (95% CI: 0.89-1.16) for women without aura, and 1.13 (95% CI: 0.98-1.3) for women with a migraine history, compared with women with no history of migraine. Due to the high degree of heterogeneity, and the lack of statistical estimates of the association in several of the reviewed studies, meta-analysis of the available data was not possible.

CONCLUSION

This study is the first review to examine the association between diabetes and migraine. Further longitudinal studies are required to clarify the migraine-diabetes association. There is also a clear need for more studies with larger sample sizes and similar methodologies in order to provide necessary information to conduct a meta-analysis.

Pathophysiological Bases of Comorbidity in Migraine

Despite that it is commonly accepted that migraine is a disorder of the nervous system with a prominent genetic basis, it is comorbid with a plethora of medical conditions. Several studies have found bidirectional comorbidity between migraine and different disorders including neurological, psychiatric, cardio- and cerebrovascular, gastrointestinal, metaboloendocrine, and immunological conditions. Each of these has its own genetic load and shares some common characteristics with migraine. The bidirectional mechanisms that are likely to underlie this extensive comorbidity between migraine and other diseases are manifold. Comorbid pathologies can induce and promote thalamocortical network dysexcitability, multi-organ transient or persistent pro-inflammatory state, and disproportionate energetic needs in a variable combination, which in turn may be causative mechanisms of the activation of an ample defensive system with includes the trigeminovascular system in conjunction with the neuroendocrine hypothalamic system. This strategy is designed to maintain brain homeostasis by regulating homeostatic needs, such as normal subcortico-cortical excitability, energy balance, osmoregulation, and emotional response. In this light, the treatment of migraine should always involves a multidisciplinary approach, aimed at identifying and, if necessary, eliminating possible risk and comorbidity factors.

Associations Between Migraine and Type 2 Diabetes in Women: Findings From the E3N Cohort Study

Importance

Little is known about the associations between migraine and type 2 diabetes and the temporality of the association between these 2 diseases.

Objective

To evaluate the association between migraine and type 2 diabetes incidence as well as the evolution of the prevalence of active migraine before and after type 2 diabetes diagnosis.

Design, Setting, and Participants

We used data from the E3N cohort study, a French prospective population-based study initiated in 1990 on a cohort of women born between 1925 and 1950. The E3N study participants are insured by a health insurance plan that mostly covers teachers. From the eligible women in the E3N study, we included those who completed the 2002 follow-up questionnaire with information available on migraine. We then excluded prevalent cases of type 2 diabetes, leaving a final sample of women who were followed up between 2004 and 2014. All potential occurrences of type 2 diabetes were identified through a drug reimbursement database. Statistical analyses were performed in March 2018.

Exposures

Self-reported migraine occurrence.

Main Outcomes and Measures

Pharmacologically treated type 2 diabetes.

Results

From the 98 995 women in the study, 76 403 women completed the 2002 follow-up survey. Of these, 2156 were excluded because they had type 2 diabetes, leaving 74 247 women. Participants had a mean (SD) age of 61 (6) years at baseline, and all were free of type 2 diabetes. During 10 years of follow-up, 2372 incident type 2 diabetes cases occurred. A lower risk of type 2 diabetes was observed for women with active migraine compared with women with no migraine history (univariate hazard ratio, 0.80 [95% CI, 0.67-0.96], multivariable-adjusted hazard ratio, 0.70 [95% CI, 0.58-0.85]). We also observed a linear decrease in active migraine prevalence from 22% (95% CI, 16%-27%) to 11% (95% CI, 10%-12%) during the 24 years prior to diabetes diagnosis, after adjustment for potential type 2 diabetes risk factors. A plateau of migraine prevalence around 11% was then observed for 22 years after diagnosis.

Conclusions and Relevance

We observed a lower risk of developing type 2 diabetes for women with active migraine and a decrease in active migraine prevalence prior to diabetes diagnosis. Further targeted research should focus on understanding the mechanisms involved in explaining these findings.

Migraine pathways and the identification of novel therapeutic targets

Introduction: Migraine is a chronic neurovascular disorder characterized by recurrent headache attacks associated with neurological and autonomic symptoms. The pathophysiological mechanisms of the disease are extremely complex, involving hypothalamic and trigeminovascular activation, cortical spreading depression, release of pro-inflammatory peptides, peripheral and central sensitization. The underlying cellular and molecular mechanisms have been scarcely investigated. Recently, genetic studies have suggested that different metabolic pathways could be involved in the pathogenesis of migraine.Areas covered: This review focuses on cellular and molecular mechanisms involved in migraine, suggesting a role for circadian clocks, ion channels, synaptic plasticity, vascular factors, ion metal homeostasis, and impaired glucose metabolism in the pathogenesis of the disease. Accordingly, the article proposes new therapeutic targets that may be of particular relevance for disease prevention.Expert opinion: Several complex molecular mechanisms are involved in setting the genetic threshold for migraine and the pathogenesis of headache attacks. Most promising new therapeutic targets are the modulation of hypothalamic activity and ion channels involved in pain transmission. Further studies in animals and humans are necessary to enhance the elucidation of the molecular mechanisms of migraine and open new avenues for disease prevention.

Plasma Glucose Levels Increase During Spontaneous Attacks of Migraine With and Without Aura

OBJECTIVE

To investigate plasma glucose changes during the ictal state of migraine compared to the interictal state.

BACKGROUND

Previous studies suggest abnormal glucose metabolism in migraine patients during and outside of attacks. It is not known if plasma glucose levels change during spontaneous migraine attacks.

METHODS

Plasma glucose levels were measured during and outside of spontaneous migraine attacks with and without aura. Plasma glucose values were corrected for diurnal variation of plasma glucose by subtracting the difference between the moving average (intervals of 2 hours) and overall mean from the plasma glucose values.

RESULTS

This was a sub-study of a larger study conducted at Rigshospitalet Glostrup in the Capital Region of Denmark. Thirty-one patients (24 F, 7 M, 13 with aura, 18 without aura) were included in the study. Mean time from attack onset to blood sampling was 7.6 hours. Mean pain at the time of investigation was 6 on a 0-10 verbal rating scale. Plasma glucose was higher ictally compared to the interictal phase (interictal mean: 88.63 mg/dL, SD 11.70 mg/dL; ictal mean: 98.83 mg/dL, SD 13.16 mg/dL, difference 10.20 mg/dL, 95% CI = [4.30; 16.10]), P = .0014). The ictal increase was highest in patients investigated early during attacks and decreased linearly with time from onset of migraine (-1.57 mg/dL/hour from onset of attack, P = .020). The attack-related increase in blood glucose was not affected by pain intensity or presence of aura symptoms.

CONCLUSIONS

We demonstrated higher plasma glucose values during spontaneous migraine attacks, independent of the presence of aura symptoms and not related to pain intensity, peaking in the early phase of attacks. Additional studies are necessary to confirm our findings and explore the possible underlying mechanisms.

The metabolic face of migraine - from pathophysiology to treatment

Migraine can be regarded as a conserved, adaptive response that occurs in genetically predisposed individuals with a mismatch between the brain's energy reserve and workload. Given the high prevalence of migraine, genotypes associated with the condition seem likely to have conferred an evolutionary advantage. Technological advances have enabled the examination of different aspects of cerebral metabolism in patients with migraine, and complementary animal research has highlighted possible metabolic mechanisms in migraine pathophysiology. An increasing amount of evidence - much of it clinical - suggests that migraine is a response to cerebral energy deficiency or oxidative stress levels that exceed antioxidant capacity and that the attack itself helps to restore brain energy homeostasis and reduces harmful oxidative stress levels. Greater understanding of metabolism in migraine offers novel therapeutic opportunities. In this Review, we describe the evidence for abnormalities in energy metabolism and mitochondrial function in migraine, with a focus on clinical data (including neuroimaging, biochemical, genetic and therapeutic studies), and consider the relationship of these abnormalities with the abnormal sensory processing and cerebral hyper-responsivity observed in migraine. We discuss experimental data to consider potential mechanisms by which metabolic abnormalities could generate attacks. Finally, we highlight potential treatments that target cerebral metabolism, such as nutraceuticals, ketone bodies and dietary interventions.

Potential Protective Mechanisms of Ketone Bodies in Migraine Prevention

An increasing amount of evidence suggests that migraines are a response to a cerebral energy deficiency or oxidative stress levels that exceed antioxidant capacity. The ketogenic diet (KD), a diet mimicking fasting that leads to the elevation of ketone bodies (KBs), is a therapeutic intervention targeting cerebral metabolism that has recently shown great promise in the prevention of migraines. KBs are an alternative fuel source for the brain, and are thus likely able to circumvent some of the abnormalities in glucose metabolism and transport found in migraines. Recent research has shown that KBs-D-β-hydroxybutyrate in particular-are more than metabolites. As signalling molecules, they have the potential to positively influence other pathways commonly believed to be part of migraine pathophysiology, namely: mitochondrial functioning, oxidative stress, cerebral excitability, inflammation and the gut microbiome. This review will describe the mechanisms by which the presence of KBs, D-BHB in particular, could influence those migraine pathophysiological mechanisms. To this end, common abnormalities in migraines are summarised with a particular focus on clinical data, including phenotypic, biochemical, genetic and therapeutic studies. Experimental animal data will be discussed to elaborate on the potential therapeutic mechanisms of elevated KBs in migraine pathophysiology, with a particular focus on the actions of D-BHB. In complex diseases such as migraines, a therapy that can target multiple possible pathogenic pathways seems advantageous. Further research is needed to establish whether the absence/restriction of dietary carbohydrates, the presence of KBs, or both, are of primary importance for the migraine protective effects of the KD.

Is Migraine Primarily a Metaboloendocrine Disorder?

PURPOSE OF THE REVIEW

The goals of this review are to evaluate recent studies regarding comorbidity between migraine and different metabolic and endocrine disorders and to discuss the role of insulin resistance as a common pathogenetic mechanism of these diseases.

RECENT FINDINGS

Recently, several studies showed that migraine is associated with insulin resistance, a condition in which a normal amount of insulin induces a suboptimal physiological response. All the clinical studies that used the oral glucose tolerance test to examine insulin sensitivity found that, after glucose load, there is in migraine patients a significant increase of both plasmatic insulin and glucose concentrations in comparison with controls. On the contrary, no association was found between migraine and type 2 diabetes, while type 1 diabetes seems to have a protective effect in the disease. Obesity and hypertension were shown to be risk factors for both episodic and chronic migraine. Metabolic syndrome has been recently associated mainly with migraine with aura and is now considered a risk factor also for medication overuse headache. Finally, a bidirectional association between migraine and hypothyroidism has been recently demonstrated, suggesting that common genetic or autoimmune mechanisms underlie both diseases. Recent studies showed that insulin receptor signaling and the related physiological responses are altered in migraine and may have a relevant pathogenic role in the disease. Further studies are warranted in order to better elucidate mechanisms underlying insulin resistance in migraine in order to develop new therapeutic strategies for this debilitating disease.

Diabetes is associated with decreased migraine risk: A nationwide cohort study

Background Results from studies on diabetes and migraine risk are conflicting, which may be due to methodological limitations. Prospective studies with long follow-up could increase our understanding of the relationship between the two diseases. Method We performed a cohort study including the whole Norwegian population alive on 01.01.2004, using prescriptions registered in the Norwegian prescription database to identify individuals developing type 1 diabetes, type 2 diabetes and migraine during follow-up (10 years). We used Cox proportional hazards regression to estimate rate ratios with corresponding 95% confidence intervals for the effect of diabetes on migraine risk, adjusting for age, sex, and educational level. Result We identified 7,883 type 1 diabetes patients and 93,600 type 2 patients during the study period. Type 1 diabetes was significantly associated with a subsequent decreased migraine risk during follow-up in the age- and sex-adjusted analyses (0.74; 0.61-0.89). Type 2 diabetes was also associated with a significantly lower migraine risk (0.89; 0.83-0.95). Further adjustment for educational level yielded similar results for both diabetes. Conclusion Both type 1 and type 2 diabetes were significantly associated with a decreased risk of migraine. This suggests that diabetes or diabetes treatment may have a protective effect on the development of migraine.

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.

Neuroendocrine signaling modulates specific neural networks relevant to migraine

Migraine is a disabling brain disorder involving abnormal trigeminovascular activation and sensitization. Fasting or skipping meals is considered a migraine trigger and altered fasting glucose and insulin levels have been observed in migraineurs. Therefore peptides involved in appetite and glucose regulation including insulin, glucagon and leptin could potentially influence migraine neurobiology. We aimed to determine the effect of insulin (10U·kg^-1), glucagon (100μg·200μl^-1) and leptin (0.3, 1 and 3mg·kg^-1) signaling on trigeminovascular nociceptive processing at the level of the trigeminocervical-complex and hypothalamus. Male rats were anesthetized and prepared for craniovascular stimulation. In vivo electrophysiology was used to determine changes in trigeminocervical neuronal responses to dural electrical stimulation, and phosphorylated extracellular signal-regulated kinases 1 and 2 (pERK1/2) immunohistochemistry to determine trigeminocervical and hypothalamic neural activity; both in response to intravenous administration of insulin, glucagon, leptin or vehicle control in combination with blood glucose analysis. Blood glucose levels were significantly decreased by insulin (p<0.001) and leptin (p<0.01) whereas glucagon had the opposite effect (p<0.001). Dural-evoked neuronal firing in the trigeminocervical-complex was significantly inhibited by insulin (p<0.001), glucagon (p<0.05) and leptin (p<0.01). Trigeminocervical-complex pERK1/2 cell expression was significantly decreased by insulin and leptin (both p<0.001), and increased by glucagon (p<0.001), when compared to vehicle control. However, only leptin affected pERK1/2 expression in the hypothalamus, significantly decreasing pERK1/2 immunoreactive cell expression in the arcuate nucleus (p<0.05). These findings demonstrate that insulin, glucagon and leptin can alter the transmission of trigeminal nociceptive inputs. A potential neurobiological link between migraine and impaired metabolic homeostasis may occur through disturbed glucose regulation and a transient hypothalamic dysfunction.

Migraine: A disorder of metabolism?

The treatment and prevention of migraine within the last decade has become largely pharmacological. While there is little doubt that the advent of drugs (e.g. triptans) has helped many migraine sufferers to lead a normal life, there is still little knowledge with respect to the factors responsible for precipitating a migraine attack. Evidence from biochemical and behavioural studies from a number of disciplines is integrated to put forward the proposal that migraine is part of a cascade of events, which together act to protect the organism when confronted by a metabolic challenge.

Combined Effects of ACE and MMP-3 Polymorphisms On Migraine Development

Migraine is a primary headache disorder which involves both genetic and environmental components. Since angiotensin-converting enzyme (ACE) and matrix metalloproteinase (MMP) share the same homology, we investigated whether the MMP-3 and ACE I/D gene variants are involved in migraine risk and whether the ACE variant might act in combination with the MMP-3 genetic variant in patients with migraine. This is the first study to evaluate the association between MMP-3 and ACE polymorphisms, and migraine. Genotypes were determined by polymerase chain reaction. The frequencies of 5A5A genotypes of the MMP-3 and D allele of ACE were significantly elevated, but II genotypes of the ACE and 6A allele of MMP-3 significantly decreased in all patients. The combined DD/5A5A and ID/5A5A genotypes increased the risk of migraine. Individuals who were homozygous for the deletion (D) allele showed increased ACE activity. Subjects with the 5A5A genotype and/or D allele or with the combined DD/5A5A or ID/5A5A might be more susceptible to migraine development. In contrast, subjects with the II and/or 6A6A genotypes may be protected from migraine development. The greater activity of the 5A5A and DD genotypes might result in vascular reactivity that is more pronounced in migraine. Taken together, our data suggest that numerous genes may influence ACE activity. Discovery of new genes might better clarify the pathogenesis of migraine and open an avenue to therapeutic strategies against migraine.

Migraine and Adiponectin: Is There a Connection?

Migraine is a common disorder, characterized by recurrent episodes of headache and associated symptoms. The full pathophysiology of migraine is incompletely delineated. Current theories suggest that it is a neurovascular disorder involving cortical depression, neurogenic inflammation and vasodilation. Various neuropeptides and cytokines have been implicated in the pathophysiology of migraine including calcitonin gene-related peptide, interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-α. There is evidence demonstrating an association between migraine and processes associated with inflammation, atherosclerosis, immunity and insulin sensitivity. Similarly, adiponectin, an adipocytokine secreted by adipose tissue, has protective roles against the development of insulin resistance, dyslipidaemia and atherosclerosis and exhibits anti-inflammatory properties. The anti-inflammatory activities of adiponectin include inhibition of IL-6 and TNF-induced IL-8 formation, as well as induction of the anti-inflammatory cytokines IL-10 and IL-1 receptor antagonist. Adiponectin levels are also inversely correlated with C-reactive protein (CRP), TNF-α and IL-6 levels. Likewise, recent studies have shown a possible correlation between CRP, TNF-α and IL-6 and migraine attacks. In addition, insulin sensitivity is impaired in migraine and obesity is a risk factor for the transformation from episodic to chronic migraine. In this review we discuss the basic science of adiponectin and its potential connection to the pathophysiology of migraine. Future research may focus on how adiponectin levels are potentially altered during migraine attacks, and how that information can be potentially translated into migraine therapy.

Systematic re-evaluation of genes from candidate gene association studies in migraine using a large genome-wide association data set

Background

Before the genome-wide association (GWA) era, many hypothesis-driven candidate gene association studies were performed that tested whether DNA variants in genes that had been selected based on prior knowledge about migraine pathophysiology were associated with migraine. Most studies involved small sample sets without robust replication, thereby making the risk of false-positive findings high. Genome-wide marker data of thousands of migraine patients and controls from the International Headache Genetics Consortium provide a unique opportunity to re-evaluate key findings from candidate gene association studies (and other non-GWA genetic studies) in a much larger data set.

Methods

We selected 21 genes from published candidate gene association studies and six additional genes from other non-GWA genetic studies in migraine. Single nucleotide polymorphisms (SNPs) in these genes, as well as in the regions 500 kb up- and downstream, were inspected in IHGC GWAS data from 5175 clinic-based migraine patients with and without aura and 13,972 controls.

Results

None of the SNPs in or near the 27 genes, including the SNPs that were previously found to be associated with migraine, reached the Bonferroni-corrected significance threshold; neither when analyzing all migraine patients together, nor when analyzing the migraine with and without aura patients or males and females separately.

Conclusion

The available migraine GWAS data provide no clear evidence for involvement of the previously reported most promising candidate genes in migraine.

Insulin resistance in migraineurs: results from a case-control study

OBJECTIVES

Several studies have suggested an association between migraine and insulin resistance (IR) without adequately addressing the issue according to migraine type. We assessed IR in subjects with migraine with aura (MwA) and migraine without aura (MwoA) to estimate the consistency of the possible association.

METHODS

In a case-control study we included case subjects with MwA and MwoA, who were consecutively selected from those referred to our Regional Headache Center from September 2011 to February 2013, and age-matched control subjects selected using general practitioners' databases. IR was calculated by means of the homeostatic model assessment of IR (HOMA-IR), β-cell function (HOMA-B), and the quantitative insulin sensitivity check index (QUICKI) measuring glucose and insulin values in a blood sample collected in the morning after overnight fasting. Data regarding anthropometric measures, comorbidity risk factors, and migraine characteristics were also recorded.

RESULTS

We recruited 50 case subjects with MwA (38 women) and 50 with MwoA (40 women) and 50 control subjects (40 women). Proportions of arterial hypertension, cigarette smoking, hypercholesterolemia, use of oral contraceptives, and mean values of the body mass index (BMI) were similar in the three groups. We found significantly different glucose values among and within groups considering case subjects with MwA and MwoA and control subjects (4.9 ± 0.6 vs 4.7 ± 0.5 vs 4.6 ± 0.5 mmol/l; P  = 0.018) in the absence of any difference in insulin (53.1 ± 24.0 vs 56.7 ± 34.4 vs 53.8 ± 24.4 pmol/l; P  = 0.811), HOMA-IR (1.6 ± 0.8 vs 1.7 ± 1.0 vs 1.6 ± 0.7; P  = 0.765), HOMA-B (121.4 ± 71.1 vs 149.2 ± 93.8 vs 162.8 ± 109.7; P  = 0.107), and QUICKI (0.36 ± 0.03 vs 0.37 ± 0.03 vs 0.37 ± 0.03; P  = 0.877) values. The logistic regression model showed increased odds of MwA in subjects exposed to the highest tertile of glucose values. This association was confirmed in the adjusted model, in which case subjects with MwA were compared with those with MwoA but not with control subjects.

CONCLUSIONS

In contrast to what has been shown by the majority of the available studies, the results of our study do not support the association of migraine with IR. As our study was not population-based and several patients had low disease activity, these findings need further confirmation.

Metabolic syndrome and migraine

Migraine and metabolic syndrome are highly prevalent and costly conditions. The two conditions coexist, but it is unclear what relationship may exist between the two processes. Metabolic syndrome involves a number of findings, including insulin resistance, systemic hypertension, obesity, a proinflammatory state, and a prothrombotic state. Only one study addresses migraine in metabolic syndrome, finding significant differences in the presentation of metabolic syndrome in migraineurs. However, controversy exists regarding the contribution of each individual risk factor to migraine pathogenesis and prevalence. It is unclear what treatment implications, if any, exist as a result of the concomitant diagnosis of migraine and metabolic syndrome. The cornerstone of migraine and metabolic syndrome treatments is prevention, relying heavily on diet modification, sleep hygiene, medication use, and exercise.

Identification of a novel ANKK1 and other dopaminergic (DRD2 and DBH) gene variants in migraine susceptibility

The dopaminergic system plays an important role in migraine and its clinical subtypes. Hypersensitization of dopamine receptor type 2 (DRD2) in migraine led to successful administration of receptor antagonists in antimigraine therapy. Ankyrin repeats and kinase domain containing 1 (ANKK1) gene in DRD2 loci is linked to comorbid neurological disorders. Dopamine beta hydroxylase (DBH) is responsible for maintaining dopamine-to-norepinephrine ratio implicated in migraine pathophysiology. Therefore, we aimed to look for association of functional variants in ANKK1 (rs1800497), DRD2 (rs6275 and rs1799732) and DBH (rs7239728 and rs1611115) genes with migraine susceptibility. The present study was carried out in two dependent cohorts (n primary = 208, n secondary = 127, n controls = 200). The results of the cohorts were pooled by meta-analysis using Fisher's and Mantel-Haenszel test. Benjamini-Hochberg false discovery rate test was used to correct for multiple comparisons. Computer algorithm-based TANGO, WALTZ and LIMBO predictions were used to evaluate the effect of missense polymorphism (rs1800497). For ANKK1 polymorphism, variant genotype and allele showed significant associations with migraine risk. A significant protective effect of variant DRD2 rs6275 polymorphism was noticed. DBH rs7239728 imparted significant risk at genotypic, allelic and carrier analyses. We identified a risk haplotype in DRD2 loci. Two genotype interactions between ANKK1rs1800497 and DBHrs72393728 polymorphisms showed significant risks. The variant gene product of ANKK1 rs1800497 was predicted with decreased aggregation of ANKK1 protein. In conclusion, we identified novel genetic variants, haplotype and gene interactions in dopaminergic pathway as potential risk factors for migraine susceptibility.

Genetic and Environmental Influences on Expression of Recurrent Headache as a Function of the Reporting Age in Twins

To explore age-related mechanisms in the expression of recurrent headache, we evaluated whether genetic and environmental influences are a function of the reporting age using questionnaire information that was gathered in 1973 for 15- to 47-year-old Swedish twins (n =12,606 twin pairs). Liability to mixed headache (mild migraine and tension-type headache) was explained by non-additive genetic influences (49%) in men aged from 15 to 30 years and additive genetic plus shared environmental influences (28%) in men aged from 31 to 47 years. In women, the explained proportion of variance, which was mainly due to additive genetic effects, ranged from 61% in adolescent twins to 12% in twins aged from 41 to 47 years, whereas individual specific environmental variance was significantly lower in twins aged from 15 to 20 years than in twins aged from 21 to 30 years. Liability to migrainous headache (more severe migraine) was explained by non-addi-tive genetic influences in men, 32% in young men and 45% in old men, while total phenotypic variance was significantly lower in young men than in old men. In women, the explained proportion of variance ranged from 91% in the youngest age group to 37% in the oldest age group, with major contributions from non-additive effects in young and old women (15–20 years and 41–47 years, respectively) and additive genetic effects in intermediate age groups (21–40 years). While total variance showed a positive age trend, genetic variance tended to be stable across age groups, whereas individual specific environmental variance was significantly lower in adolescent women as compared to older women.

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.

Meta-analysis of genome-wide association for migraine in six population-based European cohorts

Migraine is a common neurological disorder with a genetically complex background. This paper describes a meta-analysis of genome-wide association (GWA) studies on migraine, performed by the Dutch–Icelandic migraine genetics (DICE) consortium, which brings together six population-based European migraine cohorts with a total sample size of 10 980 individuals (2446 cases and 8534 controls). A total of 32 SNPs showed marginal evidence for association at a P-value<10⁻⁵. The best result was obtained for SNP rs9908234, which had a P-value of 8.00 × 10⁻⁸. This top SNP is located in the nerve growth factor receptor (NGFR) gene. However, this SNP did not replicate in three cohorts from the Netherlands and Australia. Of the other 31 SNPs, 18 SNPs were tested in two replication cohorts, but none replicated. In addition, we explored previously identified candidate genes in the meta-analysis data set. This revealed a modest gene-based significant association between migraine and the metadherin (MTDH) gene, previously identified in the first clinic-based GWA study (GWAS) for migraine (Bonferroni-corrected gene-based P-value=0.026). This finding is consistent with the involvement of the glutamate pathway in migraine. Additional research is necessary to further confirm the involvement of glutamate.

Sugar alters the level of serum insulin and plasma glucose and the serum cortisol:DHEAS ratio in female migraine sufferers

Early work has highlighted that a large percentage of migraineurs may have an altered glucidic methabolis due to carbohydrate-induced hyperinsulinism. The aim of this study was to assess the effect of sucrose on biomarkers of energy metabolism and utilization in migraineous females. A total of 16 participants (8 = Migraine, 8 = Non-migraine) at the mid-point of their menstrual cycle underwent a 15-h fast prior to ingesting 75 g sucrose dissolved in 175 g water. Blood sampling for the assessment of serum insulin, serum cortisol and serum dehydroepiandrosterone sulfate (DHEAS) and plasma glucose was conducted upon arrival at 09:00 h and then at regular 15-min intervals across a 150-min experimental period. The results showed a significant alteration in serum insulin and plasma glucose following sucrose ingestion in the migraine and non-migraine groups. In addition, significant group differences were observed in the level of serum insulin, serum DHEAS, and the cortisol:DHEAS ratio with migraine participants on average recording a higher sucrose-induced serum insulin level and lower DHEAS level and cortisol:DHEAS ratio when group data was compared. It was concluded that while sucrose consumption may potentiate serum insulin in migraineurs this does not result in the development of sucrose-induced hypoglycemia in migraine or non-migraine participants.

Vascular risk factors, endothelial function, and carotid thickness in patients with migraine: relationship to atherosclerosis

Recent studies indicated that migraine is associated with specific vascular risk profile. However, the functional and structural vascular abnormalities in migraine are rarely addressed. We evaluated the vascular risk factors, endothelial function, and carotid artery (CA)-intima-media thickness (IMT), segregators of preclinical atherosclerosis, in migraineurs. This preliminary study included 63 adults with headache (migraine with aura [n=14], migraine without aura [n=24], transformed migraine [n=6], and tension headache [n=19]) and 35 matched healthy subjects. The following vascular risks were assessed: body mass index (BMI), systolic blood pressure (SBP) and diastolic blood pressures (DBP), serum levels of C-reactive protein, fasting glucose, fasting insulin, total cholesterol, and triglycerides. Plasma endothelin (ET)-1, a vasoactive peptide produced by vascular smooth muscle cells and marker for endothelial injury and atherosclerosis, was measured. Endothelial-dependent vasoreactivity was assessed using brachial artery flow-mediated dilatation (FMD) in response to hyperemia. CA-IMT, structural marker of early atherosclerosis, was measured. Compared with control subjects, SBP, DBP, glucose, insulin, ET-1, and CA-IMT were elevated with migraine. FMD% was inversely correlated with SBP (P < .001), DBP (P < .01), glucose (P < .001), and insulin levels (P < .01). CA-IMT was correlated with BMI (P < .05), SBP (P < .01), total cholesterol (P < .01), triglycerides (P < .001), glucose (P < .001), insulin (P < .01), and FMD% (P < .05). In multivariate analysis, ET-1 was correlated with duration of illness, SBP, DBP, glucose, insulin, IMT, and FMD%. We conclude that endothelial injury, impaired endothelial vasoreactivity, and increased CA-IMT occur with migraine and are associated with vascular risk factors that strongly suggest that migraine could be a risk for atherosclerosis.

Two-stage case-control association study of dopamine-related genes and migraine

BACKGROUND

We previously reported risk haplotypes for two genes related with serotonin and dopamine metabolism: MAOA in migraine without aura and DDC in migraine with aura. Herein we investigate the contribution to migraine susceptibility of eight additional genes involved in dopamine neurotransmission.

METHODS

We performed a two-stage case-control association study of 50 tag single nucleotide polymorphisms (SNPs), selected according to genetic coverage parameters. The first analysis consisted of 263 patients and 274 controls and the replication study was composed by 259 cases and 287 controls. All cases were diagnosed according to ICHD-II criteria, were Spanish Caucasian, and were sex-matched with control subjects.

RESULTS

Single-marker analysis of the first population identified nominal associations of five genes with migraine. After applying a false discovery rate correction of 10%, the differences remained significant only for DRD2 (rs2283265) and TH (rs2070762). Multiple-marker analysis identified a five-marker T-C-G-C-G (rs12363125-rs2283265-rs2242592-rs1554929-rs2234689) risk haplotype in DRD2 and a two-marker A-C (rs6356-rs2070762) risk haplotype in TH that remained significant after correction by permutations. These results, however, were not replicated in the second independent cohort.

CONCLUSION

The present study does not support the involvement of the DRD1, DRD2, DRD3, DRD5, DBH, COMT, SLC6A3 and TH genes in the genetic predisposition to migraine in the Spanish population.

A candidate gene association study of 77 polymorphisms in migraine

Population-based studies have established an association between migraine and cardiovascular disease (CVD). We sought to investigate whether genetic variants implicated in CVD are associated with migraine. We performed an association study among 25,713 women participating in the Women's Health Study, with information on 77 previously characterized polymorphisms. Migraine and migraine aura status were self-reported. We used logistic regression to investigate the genotype-migraine association. At baseline, 4705 (18.3%) women reported history of migraine; 39.6% of the 3306 women with active migraine indicated aura. Regarding any history of migraine, the multivariable-adjusted odds ratios (95% confidence intervals) for TNF rs673 were 0.52 (0.30 to 0.89), for TGFB1 rs1800469 0.93 (0.89 to 0.98), and for CCR2 rs1799864 1.12 (1.03 to 1.21). Among active migraine with aura, the odds ratios (95% confidence intervals) were 1.35 (1.0 to 1.81) for TNF rs1800750, 1.13 (1.02 to 1.26) for TNF rs1800629, and 1.22 (1.07 to 1.40) for CCR2 rs1799864; among active migraine without aura, 0.9 (0.84 to 0.97) for TGFB1 rs1800469, 1.13 (1.01 to 1.27) for NOS3 rs3918226, and 1.12 (1.02 to 1.24) for IL9 rs2069885. After correction for multiple testing using the false discovery rate, none of the results remained significant. Our data suggest an association of polymorphisms implicated in inflammatory pathways and migraine in women. TNF, CCR2, TGFB1, NOS3, and IL9 warrant further investigation.

PERSPECTIVE

This article presents results from an association study of 77 polymorphisms, implicated in CVD, and migraine. Variants in TNF, CCR2, TGFB1, NOS3, and IL9 were found to be associated with migraine but did not remain significant after adjustment for multiple testing. Variations in these genes warrant further investigation.

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.

The vascular risk associations with migraine: relation to migraine susceptibility and progression

Migraine is a common disorder in which changes in cortical excitability, neuroinflammation and dysfunction of the vascular wall contribute to its pathophysiology. Repeated attacks of migraine over prolonged periods result in inflammatory arteriopathy of the cranial vessels. Several studies indicate that migraine is associated with special pattern of inflammatory markers and some adverse vascular risk factors including: increased levels of CRP, ILs, TNF-alpha and adhesion molecules which are markers of systemic inflammation, oxidative stress and thrombosis, increased body weight, high blood pressure, hypercholesterolemia, impaired insulin sensitivity, high homocysteine levels, stroke and coronary heart disease. Such comorbidities are not explained by bias but indicate possible shared underlying pathogenic mechanisms. Recent studies have shown involvement of cranial as well as peripheral vascular dysfunction with migraine indicating that migraine may be a local manifestation of a systemic disease rather than a primary brain phenomenon. The associated inflammatory process of migraine together with the associated adverse medical comorbidities exposes patients to endothelial vascular wall injury which further increases migraine susceptibility and progression as well as increases the risk for atherogenesis. The knowledge that migraine is a risk for vascular diseases raises important clinical implications, recommendations and future perspectives in migraine treatment and prevention.

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.

Insulin metabolism is altered in migraineurs: a new pathogenic mechanism for migraine?

BACKGROUND

Migraine is a complex biochemical dysfunction attributed to a disorder of the trigeminal and hypothalamic pathways. Impairment of glucose metabolism has been reported in migraine, but data are scanty and inconsistent.

OBJECTIVE

The main aim was to verify whether migraineurs have abnormalities of the glucose and insulin metabolism. We also studied correlations between blood glucose and insulin and between insulin levels and migraine severity.

PATIENTS AND METHODS

Patients with migraine or headache other than migraine, and healthy volunteers were included. All had general blood tests and a standard oral glucose tolerance test after a 12-hour fast, and glucose and insulin were measured.

RESULTS

Over a 6-month period, we recruited 84 migraineurs (73 women, 11 men), 25 patients with nonmigraine headache (20 women, 5 men), and 26 healthy controls (24 women, 2 men). Multivariate analysis confirmed a significant difference between groups for glucose levels (P < .0001), but no significant time interaction. The differences were mostly between migraine and healthy controls (P < .0001) and to a lesser extent between other headaches and healthy controls (P < .05). A significant difference between groups was also found for insulin (P < .0001), with a significant time interaction. The difference was confirmed for migraine compared to other headaches (P < .0001) and healthy controls (P < .0001).

CONCLUSIONS

Blood glucose levels may be high in headache patients, but do not seem to be specific to migraineurs. Insulin levels were higher in migraineurs, and seemed specific to this group. These findings are in keeping with recent reports on the effects of insulin on brain functions and lend support to the possibility that insulin is involved in the pathogenesis of migraine.

Pharmacogenetics of migraine: genetic variants and their potential role in migraine therapy

Migraine is a paroxysmal neurological disorder affecting up to 6% of males and 18% of females in the general population, and has been demonstrated to have a strong, but complex, genetic component. Genetic investigation of migraine provides hope that new targets for medications and individual specific therapy will be developed. The identification of polymorphisms or genetic biomarkers for disease susceptibility and treatment should aid in providing a better understanding of migraine pathology and, consequently, more appropriate and efficient treatment for migraineurs. In this review, we will discuss results investigating genetic biomarkers for migraine and their potential role in future therapy planning.

Genetics of migraine and pharmacogenomics: some considerations

Migraine is a complex disorder caused by a combination of genetic and environmental factors. Although family and twin studies show that there is a genetic component in migraine, no genes predisposing to common forms of the disorder, migraine with and without aura, have been identified. Patients with migraine respond differently to a given drug administered. The efficacy of therapy and the occurrence of adverse drug response are a consequence of individual variability. Genetic profiling of predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. The development of International Hap Map project could provide a powerful tool for identification of the candidate genes in this complex disease and pharmacogenomics research could be the promise for individualized treatments and prevention of adverse drug response.

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.

Nocturnal secretion of growth hormone, noradrenaline, cortisol and insulin in cluster headache remission

We have previously shown decreased, nocturnal lipolysis in both phases of cluster headache (CH). Lipolysis is stimulated by noradrenaline (NA), growth hormone (GH) and cortisol, and inhibited by insulin, hormones which are directly or indirectly regulated by the hypothalamus. Our aim was to investigate the nocturnal secretion of NA, GH, cortisol and insulin in nine CH patients in remission and 10 healthy controls. Nocturnal venous blood samples were collected in hourly intervals for analysis of NA, cortisol and insulin and in 30-min intervals for GH. We found a reduced increase in GH between 24.00 h and 01.00 h (anova, P < 0.05) in CH patients. Nocturnal secretion of NA, cortisol and insulin did not differ significantly between the groups. The altered nocturnal GH pattern that was seen in CH patients in remission might in part explain the altered nocturnal lipolysis previously found and further indicate a permanent hypothalamic disturbance in CH.