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Human endogenous retroviruses (HERVs) represent footprints of previous retroviral infection and have been termed “fossil viruses”

HERVs possess a similar genomic organisation to present day exogenous retroviruses such as human immunodeficiency virus (HIV) and human T cell leukaemia virus (HTLV)

Retroviruses in effect are retrograde, because the flow of genetic information is reversed compared with the normal pathway of molecular biosynthesis—DNA → RNA → protein. Indeed, all retroviruses necessitate the conversion of viral RNA into a cDNA intermediary, which is catalysed by the enzyme reverse transcriptase

Overall, human endogenous retroviruses constitute about 1% of the human genome”

some HERVs have been implicated in certain autoimmune diseases and cancers

A unit of sugar, phosphate, and base is strictly termed a nucleotide

human genes are composed of exons, which are transcribed and translated into amino acids

introns, which are interspersed between exons and represent non-translated regions that contribute to the large size of some genes

convincing argument for the possible involvement of HERVs in malignancy

HERVs may be involved in carcinogenesis by virtue of the expression of HERV mRNA,26 functional proteins,27 or retroviral-like particles

They may also be associated with the generation of new promoters29 or the activation of proto-oncogenes

inhibition of an effective immune response,

encode immunosuppressive proteins

“It has been suggested that HERV-K may be important in the progression of testicular germ cell tumours through inhibition of an effective immune response”

HERV-K might be important in the pathogenesis of human breast cancer

activation of proto-oncogenes of the ras family is common in many tumour types, and some studies have suggested a potential role for HERVs in ras activation