PIWIL2 and Azoospermia: Other studies have shown that SNPs in PIWIL2 (rs4871990 and rs13259097 in the promoter) were not associated with the risk of azoospermia and oligozoospermia, but SNPs in the other two members of PIWI family, PIWIL4 (rs508485) and PIWIL3 (rs11703684), were significantly associated with the risk of oligozoospermia [41–43].