GDF2 and hereditary hemorrhagic telangiectasia: In hereditary hemorrhagic telangiectasia (HHT; see [68]) mutations have been identified in the genes for two receptors of the TGFβ/BMP family, i.e., the co-receptor endoglin (for TGFβ, and BMP9 and BMP10; [69]) and the type I receptor ALK1 (for TGFβ and BMP; [70]), causing HHT often referred to as type-1 and type-2, respectively.