The human placenta is a multihormonal endocrine organ that produces hormones, enzymes, and other molecules that support fetal survival and development. Pregnancy-specific beta-1-glycoprotein (PSBG, PSG) is a major product of the syncytiotrophoblast, reaching concentrations of 100 to 290 mg/l at term in the serum of pregnant women (Horne et al., 1976 [PubMed 971765]). PSG is a member of the immunoglobulin (Ig) superfamily (Watanabe and Chou, 1988 [PubMed 3257488]; Streydio et al., 1988 [PubMed 3260773]).[supplied by OMIM, Oct 2009].