The quest for migraine genes

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.

Association of the C677T polymorphism in the MTHFR gene with migraine: a meta-analysis

There are conflicting data concerning the association between migraine and C677T polymorphism of the MTHFR gene. The C677T polymorphism reduces enzymatic capability by 50% and causes hyperhomocysteinaemia. We performed a meta-analysis of all published studies investigating the association between the MTHFR gene and migraine. Pooled odds ratios (OR) were estimated using random (RE) and fixed effects (FE) models. Among the overall 2961 migraineurs there was no significant difference compared with controls. Only in migraine with aura was the TT genotype associated with a higher risk of disease compared with the CC genotype [FE OR 1.30, 95% confidence interval (CI) 1.06, 1.58; RE OR 1.66, 95% CI 1.06, 2.59]. In the same subgroup a significant difference was observed in the comparison between TT and CT + CC genotypes (FE OR 1.32, 95% CI 1.10, 1.59; RE OR 1.63, 95% CI 1.10, 2.43). This study provides evidence for an association of the MTHFR gene only in migraine with aura.

The role of vascular and hormonal genes in migraine susceptibility

Migraine is a primary headache disorder that involves both genetic and environmental components. Migraine is considered to be a polygenic disorder with a number of susceptibility genes having a minor but nonetheless significant impact on susceptibility. Migraine candidate gene studies have concentrated mainly on genes involved in neurotransmitter pathways, however evidence also exists for a role for alterations in vascular and hormonal function in migraine susceptibility. We present here a mini-review of genetic studies, investigating the potential role of vascular and hormonal gene variants, and discuss how vascular and hormonal dysfunction may impact on migraine susceptibility. We propose that the potential role of vascular and hormonal genes in this disorder warrants further investigation.

The estrogen receptor 1 G594A polymorphism is associated with migraine susceptibility in two independent case/control groups

Migraine is a painful and debilitating disorder with a significant genetic component. Steroid hormones, in particular estrogen, have long been considered to play a role in migraine, as variations in hormone levels are associated with migraine onset in many sufferers of the disorder. Steroid hormones mediate their activity via hormone receptors, which have a wide tissue distribution. Estrogen receptors have been localized to the brain in regions considered to be involved in migraine pathogenesis. Hence it is possible that genetic variation in the estrogen receptor gene may play a role in migraine susceptibility. This study thus examined the estrogen receptor 1 (ESRalpha) gene for a potential role in migraine pathogenesis and susceptibility. A population-based cohort of 224 migraine sufferers and 224 matched controls were genotyped for the G594A polymorphism located in exon 8 of the ESR1 gene. Statistical analysis indicated a significant difference between migraineurs and non-migraineurs in both the allele frequencies (P=0.003) and genotype distributions (P=0.008) in this sample. An independent follow-up study was then undertaken using this marker in an additional population-based cohort of 260 migraine sufferers and 260 matched controls. This resulted in a significant association between the two groups with regard to allele frequencies (P=8 x 10(-6)) and genotype distributions (P=4 x 10(-5)). Our findings support the hypothesis that genetic variation in hormone receptors, in particular the ESR1 gene, may play a role in migraine.

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.

[Physiopathology of migraine]

The pathophysiology of migraine is not yet fully understood. The most important structures involved seem to be the central nervous system (cortex and brain stem), the trigeminovascular system and related cranial arteries, other autonomic fibres innervating such vessels, and various local vasoactive agents, including SP, CGRP, NO, VIP, NPY, ACh, NA, NKA, among others. The spreading depression phenomenon may explain clinical as well experimental findings in migraine. Its propagation velocity mirrors what is found in clinical aura, it may activate the spinal trigeminal nucleus and may induce CGRP and NO release. Circulatory changes detected with various imaging procedures during migraine also support the pathophysiological role of spreading depression. Three abnormal loci (chromosomes 1 and 19) have been recently found in familial hemiplegic migraine. This produces abnormalities in the voltage-dependent P/Q Ca channel, specific for the central nervous system, which regulates the release of various neurotransmitters, probably including serotonin. It is possible that a channelopathy underlies the pathophysiology of migraine, as in other paroxysmal neurological disorders secondary to membrane hyperexcitability.