• When a couple is affected by infertility, the male factor is usually ignored. However, it’s the origin of more than half of fertility problems. 

• CREA’s Clinical Andrology Department has developed a new method for sperm DNA fragmentation analysis to detect alterations in the integrity of the sperm’s genetic material.

 

At least half of the couples referred for infertility, have a male factor problem. However, when pregnancy is not achieved, most of the tests are performed to the female patient, whilst the male factor treatment is limited to a routine sperm analysis. Depending on its result, the assisted reproduction technique is chosen, ignoring the reason for which the semen quality is poor. 

In this context, specialists of CREA’s Clinical Andrology Department, assisted reproduction medical centre in Valencia, have found out how to detect alterations linked to sperm DNA integrity. Specifically, alterations linked to damages affecting both strands of this molecule containing the genetic information that the sperm must transport to the ooocyte. 

Among other consequences, these damages can give rise to recurrent miscarriages or implantation failures after assisted reproduction techniques have been performed. “The existence of double-stranded DNA breaks in a high rate of sperm is related to worst fertilization rates, even with sperm micro-injection (ICSI), as well as to higher chances of embryonic development arrest”, as pointed out by Dr. Miguel Ruiz Jorro, CREA’S co-director and Head of Clinical Andrology’s Department. 

He continues: “Nowadays we are aware of certain pathologies provoking damages in the sperm DNA. The higher the number of damages, the lower will be the integrity of the material genetic, as well as the chances of having a full-term pregnancy, especially if the breaks are affecting both DNA strands. In this case it might entail a genetic risk for the descendants. In order to improve pregnancy chances in couples with male infertility it’s fundamental to detect the cause of the fragmentation and to analyze the type of damage.  

DNA damages and its relation with mutations and cancer 

DNA damages are a natural event. Human body cells identify them and either the damage is repaired, or the cell is eliminated. This is part of the physiological process of cells renovation and control of those cells presenting alterations. 

DNA is the molecule carrying the genetic information and it’s made of two identical strands. When one strand is fragmented, the cell identifies the damage and repairs it copying the information of the identical strand. When the damage affects both strands, repair can be more complicated, although in most cases the cell can copy it from the other chromosomes of the pair, as in all the cells chromosomes are doubled. 

“However”, - Dr. Ruiz Jorro points out- “this is not happening in eggs and sperm, as they only have one pair of each chromosome. For this reason, when double-stranded breaks take place, it’s more likely that repair is defective and that, once both damaged DNA extremes join together, part of the genetic information is missing and mutations take place.” 

Cells DNA integrity, repair of damages and their consequences, are being increasingly investigated, especially for their linkage with cancer. The origin of many tumours is the lack of identification of these damages that give rise to the fact that cells are not eliminated properly and grow without control. “When fragmentation is affecting both strands, there will be more cells with mutations, thus cancer will be more heterogeneous and will have worst prognosis. Therefore it’s important to research and differentiate between simple-stranded and double-stranded DNA damages in oncology”, Doctor explains. 

The spermatozoa, a part from having one copy of each chromosome, has all its DNA in a more reduced space than the rest of cells, therefore it can transport all its genetic information to the oocyte. This size loss implies that also part of the necessary mechanisms for DNA repair are lost, in case of damages. The spermatozoa is unable to fix the damages, but it can identify them so that, once it enters into the oocyte, the egg will detect and try to repair them. 

“Depending on how much DNA has been lost in the damage, the uncorrect repair, joining both damaged extremes, can give rise to an embryo carrier of genetic alterations, such as deletions (loss of part of the DNA information), mutations (changes in the DNA organization) or aneuploidies (presence of an abnormal number of chromosomes)”, Dr. Ruiz Jorro explains. 

Sperm DNA fragmentation: the need of a simple and safe method of detection 

Sperm DNA fragmentation can be evaluated through different methods. However, most of them are very expensive and require highly specialized and qualified staff. “For this reason at CREA we have embarked on researching and developing a simple, reliable and reproducible method to detect double-stranded sperm DNA break”, Dr. Ruiz Jorro added. 

Procedure developed by CREA is based on the marking of the sperm histones, a component of its DNA that is modified when a double-stranded damage happens in that DNA area. It’s a marking system frequently used in other body’s cells, “but doing it on sperm represented a major complication for the extreme compression of its DNA,  a hundred times more than in other somatic cells. Until we finally discovered the way to do it, after a long time and a big effort from all the team”, argues Dr. Ruiz. 

This new analysis was presented by CREA’s specialists to the scientific community at the end of last year during ASEBIR’s (Association for Reproductive Biology Study) Congress  and will be exposed during the next days at the 32nd National Congress of SEF (Spanish Society for Fertility), 16th-18th May. It allows improving detection of fertility problems due to male factor and to carry out more effective and safe treatments. 

“Through the analysis performed at our lab we intend not only to achieve a simple method to detect the rate of sperm with double-stranded damages, but also to evaluate the possible relation between these damages and the presence of aneuploidies and the results of assisted reproduction treatments, regarding different concepts such as initation of oocyte activation, fertilization rate, division rate, blastocyst formation rate, embryonic euploidy, implantation rate, clinical pregnancy rate, miscarriage rate, live birth rate and rate of abnormalities in the fetus”, concluded Dr. Ruiz.