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Background: The risk of arterial diseases may be elevated among family members of individuals having multifocal fibromuscular dysplasia (FMD). We sought to investigate the risk of arterial diseases in families of individuals with FMD., Methods: Family histories for 73 probands with FMD were obtained, which included an analysis of 463 total first-degree relatives focusing on FMD and related arterial disorders. A polygenic risk score for FMD (PRS FMD ) was constructed from prior genome-wide association findings of 584 FMD cases and 7139 controls and evaluated for association with an abdominal aortic aneurysm (AAA) in a cohort of 9693 AAA cases and 294 049 controls. A previously published PRS AAA was also assessed among the FMD cases and controls., Results: Of all first degree relatives of probands, 9.3% were diagnosed with FMD, aneurysms, and dissections. Aneurysmal disease occurred in 60.5% of affected relatives and 5.6% of all relatives. Among 227 female first-degree relatives of probands, 4.8% (11) had FMD, representing a relative risk (RR) FMD of 1.5 ([95% CI, 0.75-2.8]; P =0.19) compared with the estimated population prevalence of 3.3%, though not of statistical significance. Of all fathers of FMD probands, 11% had AAAs resulting in a RR AAA of 2.3 ([95% CI, 1.12-4.6]; P =0.014) compared with population estimates. The PRS FMD was found to be associated with an AAA (odds ratio, 1.03 [95% CI, 1.01-1.05]; P =2.6×10 -3 ), and the PRS AAA was found to be associated with FMD (odds ratio, 1.53 [95% CI, 1.2-1.9]; P =9.0×10 -5 ) as well., Conclusions: FMD and AAAs seem to be sex-dimorphic manifestations of a heritable arterial disease with a partially shared complex genetic architecture. Excess risk of having an AAA according to a family history of FMD may justify screening in family members of individuals having FMD.