Additionally, transfection of the HERV-K HML-2 genome or HERV-K HML-2 env gene alone into human neuronal cells causes a decrease in cell number and retraction of neurites.37 In contrast to the above studies, a recent report did not detect any compelling differences in the transcription of HERV-K HML-2 loci in ALS versus control brain and spinal cord samples and was unable to confirm the presence of full-length HML-2 Env protein in ALS and control samples.42, Table 1 summarises the data from the above studies. Here, ERVW-1 is linked to amyotrophic lateral sclerosis.