ERVW-1 and Motor neuron atrophy: In addition, it has been reported that HSV-1, EBV, CMV, and HHV-6 can cause motor neuron degeneration by activating endogenous retroviruses, thereby inducing the expression of the envelope glycoprotein HERV-K in ALS (Medina et al., 2017; Mayer et al., 2018).