Migraine genetics

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.

The evolutionary meaning of migraine

INTRODUCTION

Migraine's astonishing prevalence and preserved genetic background contrast with the definition of a disease and the biological meaning of experiencing recurrent, severe headache attacks is still puzzling.

METHODS

To provide a comprehensive explanation of the migraine evolutionary meaning, we review (i) the putative role of the autonomic nervous system in migraine attacks, (ii) the inter-ictal autonomic, functional, and metabolic signature of migraine patients, (iii) the bio-behavioral perspective of pain, and (iv) the allostatic perception of migraine chronification.

RESULTS

Migraineurs have inter-ictal cortical hyperexcitability and metabolic dysfunction that predisposes to brain energetic imbalance. Multiple precipitating factors may lead to brain energy consumption over the migraine attack generation threshold. In response, the brain engenders adaptive, evolutionary conserved, autonomic-behavior responses through the antidromic activation of the trigeminovascular system. The sickness behavior and severe pain experienced during migraine attacks result in avoiding mental and physical activity, allowing brain energy restoration. Chronic exposure to stressors may result in an allostatic overload, leading to maladaptive chronic activation of these responses. In this bio-behavioral perspective, the chronification of migraine should be envisioned as a pathological process, whereas the migraine itself should not.

CONCLUSION

Migraine has an evolutionary (Darwinian) meaning.

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.

Targeting MTHFR for the treatment of migraines

INTRODUCTION

Migraine is a common neurovascular disorder classified by the World Health Organization as one of the most debilitating diseases. Migraine is a complex disease and is a consequence of an interaction between genetic, epigenetic and environmental factors. The MTHFR gene is one of the few replicated genetic risk factors for migraine and encodes an enzyme that is crucial for the folate and the methionine cycles. Individuals carrying the T allele of the MTHFR C677T polymorphism have increased plasma concentrations of homocysteine which leads to endothelial cell injury and alterations in coagulant properties of blood. Areas covered: This review focuses on the recent advances in genetics and the role of the MTHFR gene and homocysteine metabolism in migraine etiopathogenesis. The article summarizes the potential of targeting MTHFR and homocysteine for disease prevention. Expert opinion: Determination of MTHFR C677T polymorphisms as well as measurement of homocysteine concentrations may be useful to migraine patients, particularly those suffering from migraine with aura. Preliminary studies support the use of folate, vitamin B6 and vitamin B12 for the prevention of migraine. However, the results of these studies await replication in larger randomized controlled clinical trials.

Behavioral study of a rat model of migraine induced by CGRP

Migraine is a debilitating disorder characterized by recurrent headache arising from neurovascular dysfunction. Despite recent progress in migraine research, the exact mechanisms underpinning migraine are poorly understood. Furthermore, it is difficult to develop an animal model of migraine that resembles all symptoms of patients. In this study, we established a novel animal model of migraine induced by epidural injection of calcitonin gene-related peptide (CGRP), and examined climbing hutch behavior, facial-grooming behavior, body-grooming behavior, freezing behavior, resting behavior, and ipsilateral hindpaw facial grooming behavior of rats following CGRP injection. CGRP significantly reduced climbing hutch behavior, and face-grooming behavior, and increased immobile behavior. We also found that the P15 and P85 percentile range of behavioral data exhibited a high positive rate (83.3%) for establishing the model with less false positive rate. Our results verified that the rat model of migraine induced by CGRP featured many behaviors of migraine patients demonstrated during migraine attacks. Our findings suggest that this new model can be a useful tool for understanding the pathophysiology of migraine and studying novel therapeutic strategies for the treatment of migraine.

Cortical spreading depression as a target for anti-migraine agents

Spreading depression (SD) is a slowly propagating wave of neuronal and glial depolarization lasting a few minutes, that can develop within the cerebral cortex or other brain areas after electrical, mechanical or chemical depolarizing stimulations. Cortical SD (CSD) is considered the neurophysiological correlate of migraine aura. It is characterized by massive increases in both extracellular K⁺ and glutamate, as well as rises in intracellular Na⁺ and Ca²⁺. These ionic shifts produce slow direct current (DC) potential shifts that can be recorded extracellularly. Moreover, CSD is associated with changes in cortical parenchymal blood flow. CSD has been shown to be a common therapeutic target for currently prescribed migraine prophylactic drugs. Yet, no effects have been observed for the antiepileptic drugs carbamazepine and oxcarbazepine, consistent with their lack of efficacy on migraine. Some molecules of interest for migraine have been tested for their effect on CSD. Specifically, blocking CSD may play an enabling role for novel benzopyran derivative tonabersat in preventing migraine with aura. Additionally, calcitonin gene-related peptide (CGRP) antagonists have been recently reported to inhibit CSD, suggesting the contribution of CGRP receptor activation to the initiation and maintenance of CSD not only at the classic vascular sites, but also at a central neuronal level. Understanding what may be lying behind this contribution, would add further insights into the mechanisms of actions for "gepants", which may be pivotal for the effectiveness of these drugs as anti-migraine agents. CSD models are useful tools for testing current and novel prophylactic drugs, providing knowledge on mechanisms of action relevant for migraine.

Psychopathology in children and adolescents with primary headaches: categorical and dimensional approaches

BACKGROUND

Recurrent headache is common in childhood, but there is not a great amount of data on the associations between headaches and psychopathology in children.

OBJECTIVE

The aim of this study is to examine the relationships between primary headaches and psychopathology in children, using both the categorical and dimensional assessment.

METHODS

The sample consisted of 70 patients with primary headache compared to a matched sample of 50 healthy children. Psychiatric comorbidity was defined according to the diagnostic criteria of the Diagnostic and Statistical Manual of Disorders. Child psychopathology outcomes were assessed using child- and parent-reported standardized instruments.

RESULTS

Internalizing and externalizing problems were significantly represented among children with headaches compared to the control group, respectively 63% and 27%, without significant differences between migraine and tension-type headache children. Moreover, a total of 26% of the children with a headache reported psychiatric comorbidity such as anxiety and mood disorders.

CONCLUSION

The dimensional approach improves accuracy in the recognition of emotional and behavioral problems compared to the categorical approach; however, the use of both of these approaches could be useful for clinical practice, treatment and research.

Psychiatric comorbidities of chronic migraine in community and tertiary care clinic samples

Although the association between episodic migraine and psychiatric comorbidities is well documented, few studies have focused on the comorbidity with chronic migraine (CM) and discrepancies exist between population-based and clinic-based data. The objective of this study is to compare demographic and psychiatric comorbidity correlates between CM samples drawn from the community and tertiary care. All inhabitants from a city borough were interviewed for the presence of headaches occurring 15 or more days per month. CM was diagnosed after subjects had been interviewed and examined by a headache doctor. Participants were also assessed with a structured interview by a psychiatrist, who assigned diagnoses based on the DSM-IV. The same investigators assessed all patients consecutively seen in a university-based outpatient headache center over a 4-month period. The samples consist of 41 individuals from the community and 43 from the headache center. Sociodemographic profiles were similar between groups with the exception of the mean number of years of formal education. Among individuals from the community, psychiatric diagnoses were present in 65.9 % of cases, relative to 83.7 % in those from the headache center (p = 0.06). Phobias (41.9 vs. 29.3 %) and depression (32.6 vs. 29.3 %) were more frequent in patients from the headache center, but this difference did not reach statistical significance. Thus the frequency of psychiatric disorders in patients with CM was elevated in both settings, being higher in the specialty care clinic.

Migraine and psychiatric comorbidity: a review of clinical findings

Migraine is an extremely common disorder. The underlying mechanisms of this chronic illness interspersed with acute symptoms appear to be increasingly complex. An important aspect of migraine heterogeneity is comorbidity with other neurological diseases, cardiovascular disorders, and psychiatric illnesses. Depressive disorders are among the leading causes of disability worldwide according to WHO estimation. In this review, we have mainly considered the findings from general population studies and studies on clinical samples, in adults and children, focusing on the association between migraine and psychiatric disorders (axis I of the DSM), carried over after the first classification of IHS (1988). Though not easily comparable due to differences in methodology to reach diagnosis, general population studies generally indicate an increased risk of affective and anxiety disorders in patients with migraine, compared to non-migrainous subjects. There would also be a trend towards an association of migraine with bipolar disorder, but not with substance abuse/dependence. With respect to migraine subtypes, comorbidity mainly involves migraine with aura. Patients suffering from migraine, however, show a decreased risk of developing affective and anxiety disorders compared to patients with daily chronic headache. It would also appear that psychiatric disorders prevail in patients with chronic headache and substance use than in patients with simple migraine. The mechanisms underlying migraine psychiatric comorbidity are presently poorly understood, but this topic remains a priority for future research. Psychiatric comorbidity indeed affects migraine evolution, may lead to chronic substance use, and may change treatment strategies, eventually modifying the outcome of this important disorder.

High frequency of migraine-only patients negative for the 3243 A>G tRNALeu mtDNA mutation in two MELAS families

Migraine is associated with stroke-like episodes in mitochondrial encephalomyopathy, lactic acidosis, stroke-like syndrome (MELAS). Moreover, abnormalities of oxidative phosphorylation are also reported in migraine. We studied two maternal lineages with MELAS and chronic progressive external ophthalmoplegia (CPEO) affected probands carrying the 3243 A>G tRNALeu (MELAS) mutation, remarkable for a high frequency of subjects suffering only migraine. Thus, migraine could be a monosymptomatic expression of the MELAS mutation. We assessed the 3243 A>G tRNALeu mutational load in skeletal muscle and other somatic tissues from the migraine-only subjects, as well as lactic acid levels after exercise. All migraine-only subjects did not carry the MELAS mutation. Muscle biopsy showed mild mitochondrial abnormalities in the non-mutant, migraine-only subjects and, occasionally, abnormal lactic acid. Clear features of mitochondrial myopathy and pathological lactic acid characterised the subjects carrying the MELAS mutation. Our study demonstrates that migraine-only subjects lacked the MELAS mutation, but still had a possible mtDNA-associated genetic predisposition, being maternally related and having some evidence of impaired mitochondrial oxidative phosphorylation.

The primary headaches as a reflection of genetic darwinian adaptive behavioral responses

OBJECTIVE

The objective of this study is to present a view of the primary headaches as genetically determined behavioral responses consistent with sickness behavior and defense reaction, respectively.

BACKGROUND AND DESIGN

A review of the literature bearing on the behavioral, humoral, and functional imaging aspects of the primary headaches shows that migraine and cluster headache (CH) are pain conditions characterized by different behaviors during the attacks. Here it is postulated that the behavioral responses to migraine and CH are evolutionary conserved reactions consistent with sickness behavior and defense reaction.

RESULTS

The sickness behavior observed during migraine attacks is a pan-mammalian adaptive response to internal and external stressors, characterized by withdrawal and motor quiescence, sympatho-inhibition and lethargy, in which visceral pain signals a homeostatic imbalance of the body and/or brain. In contrast, the defense reaction in CH consists of a fight-or-flight reaction, with motor restlessness and agitation, in which pain is exteroceptive in kind.

CONCLUSION

These different behavioral responses are thus specific to different kinds of pain, distinguished by the behavioral significance of the pain (visceral pain in migraine vs exteroceptive pain in CH), and imply brain matrices involving different networks in the brainstem, hypothalamus, and forebrain regions that engender evolutionarily conserved adaptive genetic responses. Cytokines play an important role in their development. Predictions and limitations of the hypothesis are discussed together with implications for genetic studies on headaches.