TGFB1 and hyperinsulinemic hypoglycemia, familial, 4: Mutations of the fibrillin-1 (FBN1) gene which encodes the fibrillin-1 protein and mutations of the transforming growth factor β (TGF-β) receptor 2 gene are responsible for the occurrence of Marfan’s syndrome, as well as MVP.23,24 Fibrillin-1 protein is the principal component of extracellular matrix (ECM) microfibrils and also one of the regulating factors of TGF-β activity, by inhibiting it.24 In patients with fibrillin deficiency, an enhanced activity of TGF-β was noticed.