Studies have found that the expression of syncytin-1 and its receptor SLC1A5 have significantly decreased in samples with asthenozoospermic, oligozoospermic and oligoasthenozoospermic than normozoospermic samples [90], suggesting that decreased expression of syncytin-1 and SLC1A5 could be a cause of infertility. This evidence concerns the gene ERVW-1 and Infertility.