HERV and autoimmune neural diseases, illustration. Human endogenous retrovirus (HERV) in multiple sclerosis (MS, left) and amyotrophic lateral sclerosis (ALS, right), also known as motor neurone disease (MND). Human endogenous retrovirus is an example of retrovirus. Retroviruses are RNA viruses that copy their genome into the DNA of the host cell. This can then lie dormant and be passed on through the generations, when it is known as an endogenous retrovirus. If it then reactivates, it may cause certain diseases. At left, HERV-W proteins are seen with microglial cells (orange), pro-inflammatory cytokines with myelin sheath debris (pink), and the inhibition of the maturation of an oligodendrocyte progenitor cell (OPC, red). At right, HERV-K proteins are disrupting motor neurons (purple).