[5] Over the past several years, it has been found that this group of ERVs play an important role in embryogenesis, but their expression is silenced in most cell types in healthy adults.

Reactivation of it or anomalous expression of HML-2 in adult tissues has been associated with various types of cancer [7][8][9] and with neurodegenerative diseases such as amytrophic lateral sclerosis (ALS).

Human genome contains hundreds of copies of HERV-K and many of them possess complete open reading frames (ORFs) that are transcribed and translated, especially in early embryogenesis and in malignancies.

It is uncertain how long ago in primate evolution the full-length HERV-K proviruses which are in the human genome today were created.

[20] Furthermore, overexpression of the HERV-K accessory protein Rec (regulator of expression encoded by corf; Pfam PF15695) increases IFITM1 levels on the cell surface and inhibits viral infection.