The European/International FMD Registry and Initiative (FEIRI), a Prospective Study

Fibromuscular dysplasia (FMD) is an idiopathic, segmental, nonatherosclerotic, and noninflammatory disease of the musculature of arterial walls, leading to stenosis of small- and medium-sized arteries. FMD can be classified in multifocal FMD, characterized by alternation of stenosis and dilations ("string-of-beads") and focal FMD, corresponding to a solitary narrowing. While for long FMD was considered as a rare cause of renovascular disease mostly affecting young women, during the last decades, joint international efforts have led to a thorough reappraisal of the disease. In summary, (i) FMD is no more considered as a truly rare disease; (ii) FMD may be also diagnosed in men (10-20%) and at all ages; (iii) beyond arterial stenosis, FMD is often associated with dissections, aneurysms and arterial tortuosity; (iv) FMD is not restricted to renal arteries and often affects two or more arterial beds; (iv) multifocal FMD lesions are frequent in patients with Spontaneous Coronary Artery Dissection (SCAD).

Despite traditional views on the role of female hormones, mechanical factors and smoking, the pathophysiology of FMD remains largely unknown. In the last decade, research has been focused on genetic dissection of the disease and identification of biomarkers. Recent advances include: (i) identification of an association between FMD and an intronic variant of the Phosphatase and actin regulator 1 (PHACTR1) gene; (ii) identification of rare mutations in several genes such as Prostaglandin I2 Receptor (PTGIR) and Collagen type V alpha 1 chain (COL5A1) genes; (iii) documentation of mild Connective-Tissue Disease-like features and increased levels of Transforming Growth Factor-beta in patients with FMD; (iv) identification of a tentative proteo-genomic signature of the disease. All elements are thus in place to further dissect the pathophysiology of FMD and related diseases, refine clinical characterization, identify predictors of complications and improve screening, management and follow-up.

Unravelling the clinical characteristics, genetic and molecular basis of FMD nevertheless requires large numbers of well characterized patients. In order to address these challenges and generate new evidence pertaining to FMD and associated diseases, we aimed to create an overarching resource and study named "the European/International FMD Registry and Initiative" (acronym: FEIRI).

The objectives of FEIRI are:

To describe the demographic and arterial characteristics of FMD and related diseases at a global scale and according to countries and/or ethnic origin