"Typical" migraine as a complex disease: genetic epidemiology, twin and segregation analysis studies That migraine runs in families is an ancient observation. Familiarity however is not synonymous with heritability, especially given the wide prevalence of migraine and the possibility that familial occurrence is due to chance. In order to assess the heritability of migraine, e.g. the rate of variance attributable to genetic factors, the disease risk of relatives of migraine probands is determined and compared to that found in the general population. Several surveys indicated that first-and sometimes also seconddegree relatives of migraine probands show increased risk for migraine: a two-fold increased risk for migraine without aura (MO) and 1.4 for migraine with aura (MA) in the case of first-degree relatives of MO probands, and a 4-fold risk for MA in the case of first-degree relatives of MA probands [1]. An increased disease risk does not however prove heritability, since it may result from shared environmental factors. It is therefore interesting to note that at least one genetic epidemiology survey found an increased disease risk for migraine in first-degree relatives compared to spouses of migraine probands, who presumably share environmental factors at least for some time in their lives. Notably however, the relative risk for spouses was increased compared to the general population, which implies some degree of assorted mating or shared environmental influences [1]. Studies of heritability performed according to disease risk comparisons came to high rates of genetic determination, e.g. 60%-80% for MO and MA [2].Better ways of analysing heritability of migraine are studies of monozygotic versus dizygotic twins, especially when reared-together and reared-apart (adopted) identical twins are considered. Several twin studies have been performed in migraine
Pasquale Montagna Pietro Cortelli Mirella MochiAbstract Epidemiological genetic, family and twin studies show that the typical migraines carry a substantial genetic risk; they are currently conceptualized as complex genetic diseases. Several genetic association and linkage studies have been performed in the typical migraines. Candidate gene studies based on "a priori" pathogenic models of migraine (migraine as a calcium channelopathy; a mitochondrial DNA disorder; a disorder in the metabolism of serotonin or dopamine; in vascular risk factors or in the inflammation cascade; etc.) did not result in uniformely accepted findings. Linkage and genome wide scans gave evidence for several genetic susceptibility loci, still however in need of confirmation. Careful dissection of the clinical phenotypes and trigger factors shall greatly help future efforts in the quest for the genetic basis of the typical migraines.