Spermatids as gametes: indications and limitations.

The feasibility of achieving viable embryos, developing to term after transfer into the uterus, by fertilizing oocytes with spermatids has been demonstrated both in animal studies and in preliminary human clinical trials. Here we review the current clinical indications of spermatid conception and discuss the predictable success rates associated with each of these indications. Potential health hazards relating to the use of spermatids for conception are updated taking into account the risk of abnormal or incomplete epigenetic modifications of newly discovered human imprinted genes. We also add new experimental data showing the occurrence of spermatids in patients lacking spermatozoa and demonstrating that round spermatids recovered from patients with complete spermiogenesis failure (no elongated spermatids or spermatozoa ever detected in the patient's history) are often deficient in the factor(s) responsible for oocyte activation. The possible consequences of this deficiency for the occurrence of abnormal fertilization patterns and for the impairment of further preimplantation and post-implantation development are discussed. It is concluded that the development of diagnostic tests to assess the intrinsic quality of spermatids, with regard to their ability to act as gametes, is urgently needed as part of pre-treatment diagnosis before infertile couples are included in a spermatid conception programme. Centres wishing to use spermatids in human assisted reproduction should also be prepared to offer adequate diagnostic methods to control genomic imprinting abnormalities in the progeny.