In patients with slow-flow vascular malformations (SFVMs) including venous malformations (VM), lymphatic malformations (LM) or Klippel–Trenaunay Syndrome (KTS), somatic gain-of-function mutations in genes encoding phosphatidyl inositol 3-kinase alpha (PI3Kα, gene name PIK3CA) have been identified. Here, PIK3CA is linked to vascular malformation.