The influence of genetic versus environmental factors in the etiology of migraine was investigated by studies of two samples of female twin pairs - 154 raised together and 43 raised apart since infancy, in a report from the University of Kansas Medical Center, Kansas City and the University of Minnesota, Minneapolis. Tetrachoric correlations for migraine were higher in monozygotic than in dizygotic twins, for both reared-together and reared-apart samples. The heritability estimate for migraine was 52%. Nonshared environmental factors (accidents, illness, stress) and measurement errors accounted for the remaining variance in liability to migraine. 
COMMENT. Genetic factors account for 50% of migraines in women, and environmental factors such as accidents, illness, and stress are responsible for the remaining variance in liability. These US figures are almost identical to previous studies in Finland and Sweden.
Headache pathogenesis (Welch KMA) and genetics of migraine (Gardner K, Hoffman EP) are reviewed in Current Opinion in Neurology June 1998;11:193-197 and 211-216. Brain excitability is the proposed basis for migraine, and causes of neuronal excitability include mitochondrial defects, disturbed magnesium metabolism, and a calcium channelopathy. Familial hemiplegic migraine has been related to mutations in a brain calcium channel gene residing in chromosome 19p or chr 1. The larger group of migraine disorders may be associated with dopamine DRD2 receptor genes.