ERVW-1 and amyotrophic lateral sclerosis: In particular, RNA sequences of the human endogenous retrovirus of the K family (HERV-K) have been detected in motor neurons of ALS patients [6,7], and it has been observed that increased expression of HERV-K envelope protein in upper and lower motor neurons was neurotoxic and able to cause cellular degeneration [7], thus indicating the reactivation of HERV-K in the affected tissues.