In this respect, increased levels of bradykinin (BK), a hypotensive peptide that belongs to the kinin-kallikrein system (Leeb-Lundberg et al., 2005), have been detected in the vitreous of patients with diabetic retinopathy (Gao et al., 2007), and the intravitreal injection of both BK and the enzyme that produces BK from high molecular weight kininogen (prekallikrein) induce excessive permeability through the BRB causing edema in rats (Phipps et al., 2009; Clermont et al., 2011). The gene discussed is KNG1; the disease is diabetic retinopathy.