CLN5 and hereditary hemorrhagic telangiectasia: Hereditary haemorrhagic telangiectasia (HHT) arises from genetic mutations leading to loss of function of either activin receptor-like kinase 1 (ACVRL1) or endoglin (ENG), which respectively act as receptors and coreceptors for bone morphogenetic proteins (BMPs) 9 and 10.