ERVW-1 and amyotrophic lateral sclerosis: Neurovirulent strains of MuLV such as Cas-Br-E cause infection of microglial cells with neurodegeneration in the brain and spinal cord which resembles amyotrophic lateral sclerosis (ALS) and is mediated by the envelope protein of the virus (Lynch and Sharpe, 2000; Jolicoeur et al., 2003).