[Familial occurrence of cluster headache].

The familial occurrence of cluster headache was assessed in 421 probands with cluster headache, diagnosed according to the diagnostic criteria of the International Headache Society. The probands were from a neurological clinic and two departments of neurology. They received a mailed questionnaire regarding the presence of cluster headache among their relatives. All possibly affected relatives were interviewed by telephone. The questionnaire response rate was 88% (370/421). Seven probands belonged to three families. Familial occurrence of cluster headache was confirmed in 7% (25/366) of the families. Compared with the general population, first degree relatives of probands with cluster headache had a 14-fold increased risk of cluster headache, after standardization for sex and age. The second degree relatives had a twofold increased risk of cluster headache. The increased familial risk of cluster headache strongly suggests that cluster headache has a genetic cause.