A note on cluster headache in a population-based twin register

Evidence of a familial risk factor in cluster headache is accumulating and studies of twin concordance may resolve family resemblance into genetic and environmental influences. The past literature on cluster headache in twins comprises a few case reports of concordant monozygotic pairs. Swedish twin pairs with a diagnosis of cluster headache were selected through a cross-match of national registers of twin births and hospitalizations. Seventeen discordant twin pairs were found, in which it was possible to verify cluster headache status in 11 complete pairs (two monozygotic, four dizygotic, and five unlike-sexed pairs). In both members of a female monozygotic pair, migraine without aura developed after birth of the first child and remitted by menopause, whereas post-menopausal development of chronic cluster headache occurred in only one of them. The importance of individual specific factors for cluster headache was demonstrated. However, to explain familial aggregation a larger sample of affected twin pairs is necessary.