Contrary to the literature (Ovejero et al., 2020), reporting upregulation of HERV-W family in FM, our results showed downregulation of HERV-W family in all patient groups, more accentuated in FM and co-diagnosed groups than ME/CFS with respect to healthy levels (Figure 2E). Here, ERVW-1 is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.