Invited review
Sperm DNA integrity and male infertility: current perspectives

The sperm cell is designed to transmit the male DNA to the oocyte. The integrity of this DNA is an obvious requisite for normal embryo development and a successful pregnancy. Nevertheless, DNA quality, mainly the presence of DNA fragmentation, is not habitually assessed as part of sperm analysis due to the technical complexity of such an assessment and misunderstanding about its significance. Controversy still surrounds the relationship between DNA fragmentation rates in the sperm and fecundation, embryo quality and pregnancy. DNA damage may vary in type and degree. After sperm penetration, DNA damage tends to be repaired by the oocyte. The complex relationship between DNA damage and the extent and reliability of the different DNA repair pathways in the oocyte could explain the disparity of correlations with the different fertility parameters, reported in the different studies. The influence of DNA fragmentation on one or several fertility parameters seems clear. Moreover, assessment of DNA fragmentation should be considered not only in the context of infertility but integrated within the seminal study as a complementary parameter of sperm quality. This has been demonstrated in several andrological pathologies such as varicocele, infections and cancer. In addition, studies in various farm animal species show a clear influence of sperm DNA fragmentation on sperm quality and pregnancy outcome. The frequency of sperm cells with fragmented DNA tends to increase with time after sample collection or thawing of frozen straw and vary among species and among individuals within the same species. The evaluation in time may provide relevant information on the topic of sperm DNA fragmentation.