Project summary Fibromuscular dysplasia (FMD) is a non-atherosclerotic, systemic arteriopathy with excess burden on women. FMD may have varying manifestations, including hypertension, stroke and myocardial infarction, among others, depending on the arterial beds involved by arterial stenosis, aneurysm, dissection or tortuosity. Thus, the clinical diagnosis of FMD encompasses a spectrum of arterial dysplasia phenotypes, and these may be either sporadic or familial. Arterial medial fibrodysplasia underlies the pathologic arterial remodeling and susceptibility to loss of arterial integrity, and genetic susceptibility loci identified thus far implicate arterial smooth muscle and its corresponding extracellular matrix. The genetic architecture of these dysplasia- associated arterial diseases is emerging as variable, with contributions of complex genetic architecture, rare heritable variants in a subset of cases, and potential modifier genes. The proposed studies will comprehensively characterize the genetic and allelic spectrum, and test the hypothesis that the molecular and functional basis of these genetic influences, while operative in a model of locus and allelic heterogeneity, converge upon alterations of the vascular smooth muscle matricellular unit. The goal of this R35 proposal is to precisely define the genetic basis of arterial fibrodysplasia and employ relevant model systems for gene and variant mechanistic testing, resolution of genetic variants of uncertain significance, testing influences of potential modifier genes, and analysis of regulatory mechanisms, particularly those relevant to vascular sex differences. This proposal builds upon strengths in vascular disease characterization, high-throughput genetic and genomic applications, computational analysis, and molecular genetic approaches in model systems. We will conduct high throughput targeted gene sequencing to define the allelic spectrum of the involved genes in our clinical and biorepository resources, followed by hypothesis driven experiments in vascular cell and murine models for in vitro and in vivo definition of the mechanisms of the genetic findings impacting the matricellular components which are altered in arterial fibrodysplasia. The role of biologic sex and factors underlying relevant sex differences in arterial remodeling will be determined across the experiments. The outcome of this R35 and the proposed studies will be the successful integration of genomics and functional studies to provide new insights into the mechanisms of arterial dysplasia. The completion of these studies will provide critical and urgently needed biologic insights that will advance precision health objectives including disease diagnosis, prevention, and treatment, and to reduce the burden of cardiovascular morbidity and mortality.