VG5Q, also known as AGGF1, was identified by its association with Klippel-Trenaunay syndrome (KTS), a congenital vascular morphogenesis disorder. Two genetic alterations found in KTS lead to aberrant expression or function of VG5Q: a chromosomal translocation that falls within the VG5Q promoter and a glutamate to lysine point mutation at position 133. VG5Q is expressed by vascular endothelial cells in many tissues. It appears to be secreted and promotes endothelial cell proliferation following interactions with endothelial cell surfaces. VG5Q also directly interacts with TWEAK, a TNF superfamily ligand with angiogenic properties. Structurally, the FHA, G-patch, and OCRE domains of VG5Q suggest additional intracellular functions.