Studies of twins indicate a 34% to 51% genetic influence of likelihood to develop migraine headaches. This genetic relationship is stronger for migraines with aura than for migraines without aura. A number of specific variants of genes increase the risk by a small to moderate amount. Single gene disorders that result in migraines are rare. One of these is known as familial hemiplegic migraine, a type of migraine with aura, which is inherited in an autosomal dominant fashion. Four genes have been shown to be involved in familial hemiplegic migraine. Three of these genes are involved in ion transport. The fourth is an axonal protein associated with the exocytosis complex. Another genetic disorder associated with migraine is CADASIL syndrome or cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. One meta analysis found a protective effect from an angiotensin converting enzyme polymorphisms on migraine. The TRPM8 gene, which encodes for a cation channel, has been linked to migraines.
Migraines may be induced by triggers, with some reporting it as an influence in a minority of cases and others the majority. Many things such as fatigue, certain foods, and weather have been labeled as triggers; however, the strength and significance of these relationships are uncertain. Most people with migraines report to experience triggers. Symptoms may start up to 24 hours after a trigger.
Common triggers quoted are stress, hunger, and fatigue (these equally contribute to tension headaches). Psychological stress has been reported as a factor by 50 to 80% of people. Migraines have also been associated with post-traumatic stress disorder and abuse. Migraines are more likely to occur around menstruation. Other hormonal influences, such as menarche, oral contraceptive use, pregnancy, perimenopause, and menopause, also play a role. These hormonal influences seem to play a greater role in migraine without aura. Migraines typically do not occur during the second and third trimesters or following menopause.
Between 12 and 60% of people report foods as triggers. Evidence for such triggers, however, mostly relies on self-reports and is not rigorous enough to prove or disprove any particular triggers. A clear explanation for why food might trigger migraines is also lacking. There does not appear to be evidence for an effect of tyramine on migraine. Likewise, while monosodium glutamate (MSG) is frequently reported, evidence does not consistently support that it is a dietary trigger.
A review on potential triggers in the indoor and outdoor environment concluded that there is insufficient evidence to confirm environmental factors as causing migraines. They nevertheless suggested that people with migraines take some preventive measures related to indoor air quality and lighting