Endogenous retroviruses (ERVs) are sequences in the genome thought to be derived from ancient viral infections of germ cells in humans, mammals and other vertebrates, as such their proviruses are passed on to the next generation and now remain in the genome. Human endogenous retroviruses (HERVs) are suspected of involvement in some autoimmune diseases, in particular with multiple sclerosis. There are many thousands of endogenous retroviruses within human DNA, with HERVs comprising nearly 8% of the human genome and composed with 98,000 elements and fragments.