Human Endogenous Retrovirus-W (HERV-W) is the coding for a protein that would normally be part of the envelope of one family of Human Endogenous Retro-Viruses, or HERVs. HERV-W encoding sequences makes up about 1% of the human genome and are part of a superfamily of repetitive and transposable elements. There are 31 different families of HERVs that together make up about 8% of the human genome, this is four times more DNA than is devoted to protein coding genes.