Consistent with this hypothesis, studies evaluating genetic polymorphisms in the vasoconstrictor endothelin-1 gene (EDN1) were associated with increased risk of stroke risk as well as migraine (Etminan et al. 2005; MacClellan et al. 2007; MacClellan et al. 2009; Tikka-Kleemola et al. 2009). Here, EDN1 is linked to migraine disorder.