Finally, a study showing that BMP9 promotes stabilization of endothelial junctions suggests that Alk1 agonists could prevent the loss of retinal blood barrier function and permeability [46] associated with ROP and diabetic retinopathies, and thus could help prevent serious complications of vascular leakage such as macular edema. The gene discussed is ACVRL1; the disease is diabetic retinopathy.