The significance of sperm nuclear DNA strand breaks on reproductive outcome

Abstract

A growing body of evidence indicates that ejaculated spermatozoa from men being treated with intracytoplasmic sperm injection contain nuclear abnormalities. Many of these nuclear anomalies manifest themselves as breaks in the sperm nuclear DNA. This review examines the mechanisms involved in generating DNA strand breaks during spermatogenesis in the human, the main techniques used to assess the sperm nucleus and the evidence, in relation to assisted reproduction, showing that sperm nuclear DNA strand breaks may impact on reproductive outcome. Techniques such as the TUNEL assay and the sperm chromatin structure assay both show increased levels of DNA abnormalities in spermatozoa from men who have poor semen parameters. The reproductive parameters affected by an increased presence of DNA abnormalities in ejaculated spermatozoa include fertilization, blastocyst development, and pregnancy rates. There is accumulating evidence linking sperm nuclear DNA anomalies to poor reproductive outcome in relation to assisted reproduction technologies. The tests currently available only provide an inkling of the impact of sperm nuclear DNA abnormalities on reproductive outcomes. Although the impact an abnormal paternal genome may have on reproductive outcome is unquestionably less than that of its female counterpart, it cannot be ignored.