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.