Familial clustering of migraine: further evidence from a Portuguese study.

OBJECTIVE Our aim was to evaluate familial aggregation of migraine in a large group of Portuguese families, and to assess if familial aggregation differs between MA and MO. METHODS Familial aggregation was evaluated by estimating relative risk (RR) of migraine in 143 first-degree relatives of 50 probands with MA, in 196 first-degree relatives of 94 probands with MO and also in proband's spouses. Probands were enrolled in the study from a clinical sample and a population sample was used as reference. RESULTS A significantly increased risk of migraine was found in both first-degree relatives of MO probands (RR = 3.7; 95% CI: 3.2-4.3) and of MA probands (RR = 3.6; 95% CI: 3.1-4.3), comparatively to the general population. Risk for spouses was not increased. First-degree relatives of MA probands and MO probands had a significantly increased risk of both MA and MO compared to the general population. In the group of MA probands, RR of MA in first-degree relatives reached a significant 4-fold increase when compared with RR of MO (RR(MA|MA) = 12.2, 95%CI: 7.7-19.5; RR(MO|MA) = 3.1, 95%CI: 2.5-3.8), while, in the group of MO probands, RR of MA was not significantly increased when compared with RR of MO (RR(MA|MO) = 5.3, 95%CI: 3.1-9.2; RR(MO|MO) = 4.0, 95%CI: 3.5-4.7). CONCLUSIONS The present study focus on familial aggregation of migraine in a Portuguese population. Our results demonstrate a substantial familial risk of migraine with evidence of both common and specific etiologic mechanisms for either migraine subtypes.