The human pregnancy-specific glycoproteins (PSGs) are a family of proteins that are synthesized in large amounts by;placental trophoblasts and released into the maternal circulation during pregnancy. Molecular cloning and analysis of;several PSG genes has indicated that the PSGs form a subgroup of the carcinoembryonic antigen (CEA) gene family, which;belongs to the immunoglobulin superfamily of genes. Members of the CEA family consist of a single N domain, with;structural similarity to the immunoglobulin variable domains, followed by a variable number of immunoglobulin;constant-like A and/or B domains. Most PSGs have an arg-gly-asp (RGD) motif, which has been shown to function as an;adhesion recognition signal for several integrins, in the N-terminal domain (summary by Teglund et al., 1994 (PubMed;7851896)). For additional general information about the PSG gene family, see PSG1 (MIM 176390).