Genetic contributory factors to infertility
Keywords: Preimplantation genetic screening (PGS)
Unexplained infertility
Aneuploidy
Embryo
Preimplantation genetic diagnosis (PGD)
Infertility
Whole genome sequencing

Introduction: In recent years, the average age of first reproduction has risen significantly, the mean now standing at around 30 years in many countries. The adverse effects of maternal age on fertility and reproduction have been well documented. However, the influence of paternal age on fertility, reproduction and postnatal health is relatively poorly understood, and 50% of all male infertility cases are classed as idiopathic or unexplained infertility.
Methods: The aim of this study was to investigate factors that contribute to male infertility, split into two main parts. The first part focused on analysing data collected from patients who had undergone fertility treatment to assess the influence of different factors on infertility, especially at the genome level. The second part attempted to deal with some of the technical challenges of screening and diagnostic methods to study the genome, with the aim of providing tools that would assist future studies in pinpointing genetic factors responsible for infertility, especially in cases of idiopathic infertility.
Results: Based on data from the first part of the study, it was determined that advanced paternal age can affect sperm progressive motility, sperm DNA integrity and the fertilisation rate of in vitro fertilisation (IVF) cycles, as well as the development of embryos. Direct analysis of sperm DNA fragmentation (SDF) and degradation levels revealed an association between elevated SDF and impaired embryo development. Furthermore, a correlation was shown between chromosome aneuploidy and variance in SDF and sperm DNA degradation. Moreover, aneuploidy can influence abnormal sperm morphology and consequently also progressive motility. Also, embryo development rate of IVF cycles on day three, demonstrated a significant decline in cycles where the sperm used for fertilisation had a high aneuploidy rate, which can highlight the reduced developmental capacity of aneuploid embryos. From the lifestyle factors assessed, only alcohol consumption significantly correlated with the sperm DNA damage. Therefore, poor semen quality may highlight damage that has been incurred by the sperm DNA. When the semen quality is suboptimal, the intracytoplasmic sperm injection (ICSI) technique is suggested as a standard strategy to improve the prognosis of ART. However, when the progressive motility is poor, the ICSI approach is not as effective. Based on our findings and in line with other studies, the only sperm parameter that can be affected by paternal age is sperm motility, which could be an indicator of SDF. Therefore, the decline in ICSI fertilisation rate in patients with impaired sperm progressive motility could be due to sperm DNA damage, and even ICSI cannot improve the fertilisation rate considerably.
Discussion: The aim of the second part of this project was to establish a robust workflow for whole- genome amplification (WGA) and whole-genome sequencing of single cells to improve the coverage rate and fidelity, with the aim of providing means of detecting any mutation in the genome that might be responsible for reduced embryonic developmental competence. Towards this end, the efficiencies of two different WGA protocols (REPLI-g and TruePrime) were compared. Multiple technical factors required optimisation in order to create a suitable protocol. Our results demonstrated the overall superiority of REPLI-g compared to TruePrime in almost all the assessed parameters. The amplification rate of REPLI-g was much faster than that of TruePrime, and prolonged incubation led to overamplification and an increased duplication rate. However, the TruePrime method has a slower amplification rate and therefore, by increasing the incubation time, it was possible to improve the quality of the data. The modified protocol with reduced volume also had the most promising outcome in terms of the data produced, and could fulfil our expectations by being fast, cost-effective and efficient.
Conclusion: In conclusion, the results from the first part of this study confirmed the negative impact of male age on assisted reproductive treatments, which can result in decreased success rates of fertilisation. Other factors such as sperm DNA damage may also contribute to this age effect, suggesting that assessing this parameter prior to fertility treatment, and attempting to mitigate elevated levels of sperm DNA damage, may be of value to older patients. Additionally, overcoming the technical challenges in studying genetic contributory factors in infertility is a promising step toward better understanding of the mutations and variations that are involved in this phenomenon.