An Endogenous retrovirus (ERV) is genetic insertion in an organism's genome from an inactivated retrovirus. A retrovirus stores its genetic information in RNA and must reverse transcribe it into DNA using the protein Reverse Transcriptase before insertion into the host's genome using the protein DNA Integrase, both of which are packaged inside the capsid with the viral RNA. This process is prone to error and sometimes the errors will inactivate the gene. When these inactivate genes are inserted in the germ line of the host all its descendants will also have the inactivated insertion. Human endogenous retroviruses (HERV) have been linked to several autoimmune diseases such as multiple sclerosis.