Migraine is a tricky disorder to make sense of, as there is not a single cause of an attack. Instead, there is the concept of the migraine nociceptive unit. This takes into account that there are multiple tissues that contribute to migraine pain, including in the endothelium, vascular smooth muscle, perivascular nerves, and mast cells.
A key question in migraine research is how signaling in these different cell types is integrated into what the patient experiences during a migraine attack.
Aura is not the only indicator of migraine
It is not a simple question to answer, as each patient’s experience can be very different. There are over 100 types of migraine in the ICHD-3 classification, which is chaired by Professor Olesen [read more here]. Whilst many doctors are aware of aura symptoms, most do not realize that migraine without aura is the most common form, and so it may often not be correctly diagnosed.
Many doctors are not aware that migraine usually occurs without aura
Migraine without aura can be studied using inducers such as nitric oxide producers1 or calcitonin gene-related peptide (CGRP)2, but the underlying causes are still not well known.
Migraine is a genetic disorder
It is already known that migraine has a strong genetic component, with an estimated heritability of 38% to 53%.3,4 Studies showed a higher concordance rate of migraine in monozygotic twins (34%) than in dizygotic twins (12%).5
Some rare conditions such as familial hemiplegic migraine have been shown to be caused by mutations in single genes. However, the affected genes in this condition do not appear to be involved in the more common forms of migraine and can therefore not be used to identify these.
The Brainstorm consortium found a significant association between genes involved in migraine and in some psychiatric disorders
Interestingly, the Brainstorm consortium found that genes involved in migraine correlate weakly but significantly with genes involved in major depressive disorder (MDD), attention deficit hyperactivity disorder (ADHD) and Tourette’s syndrome.6
New studies bring new possibilities
Investigations of the genetics of migraine need large genome-wide association studies. The most recent, which is in press, included 100000 cases of migraine and 400000 controls. It identified 123 genes of interest with a minor allele frequency of more than 1%. Professor Olesen shared his excitement about what could be found by repeating Brainstorm with these newly discovered variants.
A recent genome-wide association study found 123 gene variants associated with migraine
These genes show preferential expression in the vascular smooth muscle and the brain. However, the effect size is relatively low, and there is no obvious causality from these genes. An interesting result was that a few variants were associated specifically with migraine with aura or migraine without aura. The majority of variants were seen in both.
As migraine has a high prevalence to start with7, it is hard to find any gene variants with a high relative risk of migraine. A study of extended families failed to find any genes with a relative risk of even 2.8 This makes it challenging to focus research into what the causal effects of these variants might be.
Epigenetics is a potential player in some newly discovered gene variants
However, current research on some of the rare variants suggests that altered binding of polycomb elements may change gene expression through epigenetic mechanisms.8
Genetic analysis is therefore a promising approach in migraine, but our level of understanding of the complex interaction of genetics, epigenetics, and environment is still in its early phase, making predictive analyses a challenge.