HERV-FRD (Human Endogenous Retrovirus FRD Envelope Protein) belongs to the W family of the HERV family. Also known as Syncytin-2, this protein is a key member of the syncytin family and is encoded by an env gene from an ancient retrovirus integrated into the host genome. It primarily mediates cell-cell fusion, which is essential for forming the placental syncytiotrophoblast and maintaining normal pregnancy. Furthermore, HERV-FRD exhibits immunosuppressive functions: its transmembrane subunit contains an immunosuppressive domain that inhibits maternal immune rejection of the fetus and protects the placenta from immune attack. Abnormal expression of HERV-FRD is associated with pregnancy-related disorders such as preeclampsia and intrauterine growth restriction, as well as with the development and progression of certain cancers.