ERVW-1 and myeloid sarcoma: MSRVenv and syncytin-1 proteins share several biological features, and are potentially pathogenic: they have pro-inflammatory and superantigenic properties, and have been shown to cause neurotoxic effects in vitro and in humanized or transgenic animal models [10]–[11]: they may cause neuroinflammation, neurodegeneration, alterations of the immune system and stress responses; both have been suggested as co-factors triggering the immuno-pathogenesis of MS.