Assessment of Sperm DNA Integrity and Implications for the Outcome of ICSI Treatments

Germline mutations are a driving force behind genome evolution and genetic disease. We investigated genome-wide mutation rates and spectra in multi-sibling families. Mutation rate increased with paternal age in all families, but the number of additional mutations per year differed more than two-fold between families. Meta-analysis of 6,570 mutations showed that germline methylation influences mutation rates. In contrast to somatic mutations, we found remarkable consistency of germline mutation spectra between the sexes and at different paternal ages. 3.8% of mutations were mosaic in the parental germline, resulting in 1.3% of mutations being shared between siblings. The number of these shared mutations varied significantly between families. Our data suggest that the mutation rate per cell division is higher during both early embryogenesis and differentiation of primordial germ cells, but is reduced substantially during post-pubertal spermatogenesis. These findings have important consequences for the recurrence risks of disorders caused by de novo mutations.

The earliest stages of development in most animals, including the few mammalian species that have been investigated, are regulated by maternally inherited information. Dependence on expression of the embryonic genome cannot be detected until the mid two-cell stage in the mouse, the four-cell stage in the pig (J. Osborn & C. Polge, personal communication), and the eight-cell stage in the sheep. Information about the timing of activation of the embryonic genome in the human is of relevance not only to the therapeutic practice of in vitro fertilization and embryo transfer (IVF), but more importantly for the successful development of techniques for the preimplantation diagnosis of certain inherited genetic diseases. We describe here changes in the pattern of polypeptides synthesized during the pre-implantation stages of human development, and demonstrate that some of the major qualitative changes which occur between the four- and eight-cell stages are dependent on transcription. In addition, it appears that cleavage is not sensitive to transcriptional inhibition until after the four-cell stage.

The sperm chromatin structure assay (SCSA) has been suggested as a predictor of fertility in vivo as well as in vitro. The available data however, have been based on limited numbers of treatments. We aimed to define the clinical role of SCSA in assisted reproduction. A total of 998 cycles [387 intrauterine insemination (IUI), 388 IVF and 223 ICSI] from 637 couples were included. SCSA results were expressed as DNA fragmentation index (DFI) and high DNA stainable (HDS) cell fractions. Outcome parameters were biochemical pregnancy (BP), clinical pregnancy (CP) and delivery (D). For IUI, the odds ratios (ORs) for BP, CP and D were significantly lower for couples with DFI >30% as compared with those with DFI 30% group, the results of ICSI were significantly better than those of IVF. DFI can be used as an independent predictor of fertility in couples undergoing IUI. As a result, we propose that all infertile men should be tested with SCSA as a supplement to the standard semen analysis. When DFI exceeds 30%, ICSI should be the method of choice.