[Genetics and male infertility]

Infertility is a problem affecting many couples with a child wish. In about half of these couples a male factor is (co-) responsible for the fertility concern. For part of these patients a genetic factor will be the underlying cause of the problems. This paper gives an overview of the studies performed in the Department of Embryology and Genetics of the Vrije Universiteit Brussel and the Centre for Medical Genetics of UZ Brussel in order to gain more insight into the genetic causes of male infertility. The studies, focusing on men with fertility problems, can be subdivided into three groups: studies on deletions on the long arm of the Y chromosome, studies on X-linked genes and studies on autosomal genes. It is obvious that Yq microdeletions should be considered as a cause of male infertility. Only for patients with a complete AZFc deletion, a small number of spermatozoa can be retrieved. However, even for these patients assisted reproductive technologies are necessary. Complete AZF deletions are found in 4.6% of the patients visiting the centres for Reproductive Medicine and Medical Genetics of the UZ Brussel and for whom no other cause of the fertility problems have been detected. Taken into consideration this low prevalence of Yq microdeletions, it is obvious that also other factors, including genetic factors, must be causing fertility problems. Potentially, gr/gr deletions (partial deletions of the AZFc region) might influence the fertility status of the patients. It remains, however, unclear which of the genes located in the deleted regions are important for the progression of spermatogenesis, in case of partial or complete AZF deletions. In our studies we have also investigated mutations in genes located on the X chromosome. In analogy to the Y chromosome, the X chromosome is interesting in view of studying male infertility since men only have a single copy of the sex chromosomes. As a consequence, mutations in genes crucial for spermatogenesis will have an immediate impact on the sperm production. The genes NXF2, USP26 and TAF7L were investigated for the presence of mutations. All observed single nucleotide changes were also present in control samples, questioning their relationship with male infertility. We also studied five autosomal genes: SYCP3, MSH4, DNMT3L, STRA8 and ETV5. Only for the genes STRA8 and ETV5, changes were detected that were absent in a control population existing of men with normozoospermia. Functional analysis of the changes in ETV5 and the localization of the change observed in STRA8 showed that also these alterations were probably not the cause of the fertility problems in these men. It can be concluded that mutations are rarely detected in men with fertility problems. This low frequency of mutations has also been confirmed in several published studies. Therefore, further research is necessary to determine the impact of genetic causes on male infertility.