Background: Intravenous infusion of adenylate cyclase-activating polypeptide-38 (PACAP38) provokes migraine-like attacks in 65-70% of migraine sufferers. Whether aggregation of migraine in first-degree relatives contributes to this discrepancy in PACAP38-induced response is unknown. We hypothesized that genetic enrichment plays a role in triggering of migraine and that migraine without aura patients with a high family load (>= 2 first-degree relatives with migraine) would report more migraine-like attacks after intravenous infusion of human PACAP38. Methods: In this study, we allocated 32 previously genotyped migraine without aura patients to receive intravenous infusion of 10 pmol/kg/min PACAP38 and recorded migraine-like attacks including headache characteristics and associated symptoms. Information of familial aggregation was obtained by telephone interview of first-degree relatives using a validated semi-structured questionnaire. Results: PACAP38 infusion induced a migraine-like attack in 75% (nine out of 12) of patients with high family load compared to 70% (14 out of 20) with low family load (P = 0.761). In an explorative investigation, we found that the migraine response after PACAP38 was not associated with the risk allele of rs2274316 (MEF2D), which confers increased risk of migraine without aura and may regulate PACAP38 expression. Conclusion: Migraine response to PACAP38 infusion in migraine without aura patients is not associated with high family load or the risk allele of rs2274316 (MEF2D).