The abnormally high levels of the HERV-W Env gene product were detected in the plasma of the patients with schizophrenia and bipolar disorder (Diem et al., 2012), and in the active lesions in multiple sclerosis (van Horssen et al., 2016) and in the biopsies from the chronic inflammatory demyelinating polyradiculoneuropathies (Faucard et al., 2016). The gene discussed is ERVW-1; the disease is bipolar disorder.