Endothelial dysfunction [19,27,35] or diminished vascular endothelial growth factor (VEGF) expression during the embryogenic life [49] could be responsible for the impaired collateral development in VDR deficiency since both VEGF and endothelial nitric-oxide synthase deficiency appears to disturb collateral development [50,51,52]. Here, VEGFA is linked to endothelial dysfunction.