**Conflict of interest**

*Innovations in Assisted Reproduction Technology*

biopsy to obtain a sample.

explored.

**7. Conclusions**

Obviously, further studies are needed to assess whether any effects of male age and

In order to be able to distinguish between "benign" paternal epigenetic alterations that can be repaired spontaneously, on the one hand, and clinically relevant alterations that can cause negative effects on the embryonic, fetal and offspring health, studies are needed to relate DNA methylation status of specific genes and the expression pattern of specific small RNAs with specific developmental abnormalities. This work can be done by analyzing nucleic acids extracted directly from sperm cells or by using the "liquid biopsy" approach, based on the use of soluble nucleic acids isolated from blood plasma or seminal fluid. This latter approach is particularly interesting in azoospermic men so as to avoid the need for testicular

The identification of the developmentally relevant sperm epigenetic abnormalities is a necessary pre-requisite to design possible therapeutic interventions. These may go from relatively simple to more complex ones. It has been shown in the mouse that several waves of microRNAs and tRNA fragments are shipped to sperm during post-testicular maturation in the epididymis [98]. If some pathogenic paternal epigenetic signals are conveyed to sperm essentially during epididymal passage, ICSI with spermatozoa retrieved surgically from the testis, the technique already used with success in men with elevated levels of sperm DNA fragmentation [99, 100], might be a relatively simple and immediately available solution. If this approach is not possible, other, more sophisticated technologies, such as injecting specific microRNA molecules, capable of repairing specific epigenetic defects, into the early zygote [98] or induction of DNA methylation of the genes of interest by a Dnmt3-type *de novo* DNA methyltransferase targeted to the corresponding sperm DNA sequence by a nuclease-inactivated CRISPR variant (dCas9) [101], may be

Since the availability of cell micromanipulation technologies enabling fertilization of human oocytes by ICSI with immature (testicular) spermatozoa and by round spermatid injection (ROSI), the role of paternal factors on embryonic, fetal, and offspring health needed a profound revision. While genetic abnormalities contributed by injected spermatozoa or spermatids can be controlled by preimplantation genetic testing and usually lead to a miscarriage, sperm-borne epigenetic abnormalities are much more difficult to detect and may be at the origin of different health problems throughout the offspring life. The current knowledge of the origin, nature, and mechanism of action of these sperm-borne epigenetic factors is outlined in this chapter. Surprisingly, in spite of multiple types of sperm epigenetic abnormalities associated with defective spermatogenesis and male aging, the current clinical experience is reassuring. In fact, no significant increase in the prevalence of diseases attributable to abnormal genomic imprinting was detected in children conceived by testicular spermatozoa or spermatids, probably because of the existence of efficient

repair mechanisms acting in postfertilization stages of development.

applicable in these cases are discussed.

By contrast, there is increasing evidence suggesting that transgenerational inheritance of paternally acquired epigenetic abnormalities via spermatozoa is more frequent than previously thought and can occur even in cases with normal conventional sperm parameters and during natural conception. The known pathologies transmitted in this way include neurological disorders, obesity, and diabetes, and their list is in continuous expansion. Future diagnostic and therapeutic possibilities

sperm parameters on the offspring health status can be detected later in life.

**82**

The author declares no conflict of interest related to this chapter.
