ACVRL1 and diabetes mellitus: 2018).Moreover, in the same study, ALK1 expression was downregulated in the diabetic retinal bloodvessels of wild type mice and Alk1 heterozygotes (presumably expressing 50%of the wild type levels of the protein) were characterized by a dramatically exacerbatedretinal vascular leakage evoked by diabetes, indicating Alk1haploinsufficiency.