Protocadherin-12 (PCDH12; also called VE-Cadherin-2) is an approximately 150 kDa glycoprotein belonging to the δ2 subgroup of non-clustered protocadherins. These are type I transmembrane proteins that exhibit calcium-dependent but relatively weak homophilic adhesion (1-4). Like other δ2 protocadherins, mature Protocadherin-12 contains six cadherin domains in its extracellular domain (ECD), a transmembrane sequence, and a cytoplasmic domain (1). Within the ECD, mouse Protocadherin-12 shares 95% and 82% amino acid sequence identity with rat and human Protocadherin-12, respectively. Protocadherin-12 is expressed in mouse endothelial, glycogen-rich trophoblast, and mesangial cells where it clusters at intercellular junctions (1, 2). It may be important during placental development, as placentas from Protocadherin-12-deficient mice display altered morphogenesis and transcription profiles (3). In humans, the ECD of Protocadherin-12 can be shed via proteolytic cleavage (5). It circulates at increased levels in sera from pregnant women exhibiting pre-eclampsia compared to women with nonpathological gestations (5).