Familial occurrence of cluster headache.

The familial occurrence of cluster headache was assessed in 421 patients with cluster headache, diagnosed according to the operational diagnostic criteria of the International Headache Society. The patients were recruited from a neurological clinic and two departments of neurology, covering east central Jutland and Copenhagen County respectively. They received a mailed questionnaire regarding the presence of cluster headache among their first and second degree relatives. All possibly affected relatives were interviewed by telephone. The response rate to the questionnaire was 88% (370/421). Seven patients belonged to three families. A positive family history of cluster headache was found in 7% (25/366) of the families. Compared with the general population, the first and second degree relatives of the 370 patients with cluster headache had a 14-fold and twofold increase in the risk of having cluster headache after standardisation for sex and age. This increase in familial risk strongly suggests that cluster headache has a genetic cause.