ACVRL1 and arteriovenous hemangioma/malformation: Its core pathogenesis involves mutations in the ENG (encoding the TGF-β type III receptor) or ACVRL1 (ALK1, encoding the TGF-β type I receptor) genes, leading to dysfunction of vascular endothelial cells and subsequent development of systemic capillary telangiectasia and arteriovenous malformations (AVMs) (1).