Transgenic mice deficient in TGF-β-1, TGF-β receptor 1 (ALK1), TGF-β receptor 2 (ALK4), or the accessory TGF-β-binding protein endoglin, suffer from defects in angiogenesis and vascular malformations (reviewed in [16,17]). The gene discussed is ACVR1B; the disease is vascular malformation.