ERVW-1 and obesity due to melanocortin 4 receptor deficiency: Syncytin-1 expression is higher in neuronal cells of patients with multiple sclerosis (Antony et al., 2004), a condition characterized by chronic inflammation (Pegoretti et al., 2020), which is also observed in the metabolic environment associated with obesity/increased BMI (Lumeng and Saltiel, 2011).