The genetic causes of male infertility: a Middle East and North Africa perspective

Introduction

Infertility represents the inability to achieve pregnancy after twelve or more months of regular unprotected sexual intercourse, and it affects about 15% of couples of reproductive age. Of the total cases, 50% are attributable to the male factor (Vander Borght and Wyns 2018). Not until recently, infertility represented a reproductive health disorder that was neglected, especially in the MENA region. In 2012, Mascarenhas et al. reported that infertility prevalence was highest in South Asia, Sub-Saharan Africa, North Africa and the Middle East, Central/Eastern Europe and Central Asia (Mascarenhas et al. 2012). Six years later, Eldib and Tashan (2018) showed that the incidence of primary infertility (inability to conceive after 12 or more months of regular unprotected sexual intercourse) in the Middle East and North Africa region (MENA) region is estimated at 3.8%, and secondary infertility (incapacity to conceive after 5 years of previous live birth) at 17.2%, while demographic infertility (failure to achieve conception with live birth within 5 years of exposure, based on a consistent union status, lack of contraceptive use, non-lactating and maintaining a desire for a child (Mascarenhas et al. 2012)) is estimated at 22.6% (Eldib and Tashani 2018). Recently, Sun et al. reported that the global age-standardized prevalence of infertility has increased by 23.184%, with the prevalence of male infertility estimated at 8.224%. The variations in the prevalence of male infertility across different populations were also noted (Sun et al. 2019). The Western Sub-Saharan African population have the highest rates of age-standardized male infertility at 1800 infertile men per 100,000, whereas Australasia has the lowest rates, approximately 200 infertile men per 100,000 (Sun et al. 2019). According to the same study, infertility rates in the MENA region are well above Central Europe, Western Europe, South-East Asia amongst several others at 800 infertile men per 100,000. Out of the three countries that presented with an increase in the trend of male infertility, two are from the MENA region. One is from the Middle East (Turkey; 1.498%) and the other is from North Africa (1.676%) (Sun et al. 2019). Since demographic infertility in the MENA region is on the high side (Eldib and Tashani 2018), and as well as the trend in male infertility (Sun et al. 2019), it is of utmost importance to investigate the causes.

Utilizing the World Health Organization diagnostic classification for male infertility (Organization 2018), studies have elucidated azoospermia, oligozoospermia, asthenozoospermia, teratozoospermia, or combinations thereof, as part of the causes of male infertility (Ikechebelu et al. 2003, Punab et al. 2017). A study conducted in Turkey revealed that 32% of the infertility cases was due to the male factor, who were either azoospermic or oligozoospermic (Karabulut et al. 2018). Even with the discovery of different causes of male infertility using semen analysis, diagnosing male infertility is complex due to a wide variety of genetic aberrations associated with the condition.

During the past decade, genetic studies have made great progress in elucidating the causes of male infertility, which include chromosomal translocations, azoospermia factor (AZF) deletions, Klinefelter syndrome, cystic fibrosis, and Noonan syndrome (Elsawi et al. 1994, Okada et al. 1999, Sokol and Shapiro 2001, Dhanoa et al. 2016, Kuroda et al. 2020). Some studies have identified chromosomal translocations as the most common structural genetic aberration seen in men, with nearly 1.23 per 1000 (Chen 2007, Kuroda et al. 2020). Until recently, genetic testing for chromosomal aberrations and AZF deletions are the only ways to come to a conclusive diagnosis of genetic abnormality induced male infertility. The optimal treatment plans for treating idiopathic male infertility have remained unclear unlike for established conditions such as hypogonadotropic hypogonadism and retrograde ejaculation. In order to get more informed about the genetic causes of male infertility, especially in the MENA region, the current study aimed to analyse the literature extensively regarding the effect, and the common genetic aberrations leading to male infertility from the MENA region perspectives. The epidemiological relevance of genetic anomalies induced male infertility was also discussed.

Literature search

To explore the common genetic aberrations in the MENA region, a thorough literature search was performed following the methodology of the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) guidelines. Since the MENA countries include Algeria, Bahrain, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman, Palestine, Qatar, Saudi Arabia, Syria, Tunisia, Turkey, United Arab Emirates, and Yemen, the search terms integrated each country with other parameters, such as “male infertility”, and “genetic alteration”. The literature search was performed on PubMed, Google Scholar, and Science Direct databases, retrieving articles that included male patients above the age of 18 from the MENA region, and research articles published between 1999 and 2020.

Following the search, a total of 126 articles was retrieved, of which 12 were duplicates and another 69 articles did not meet the inclusion criteria. Studies excluded were those that had patient populations originating outside the MENA region, review articles, non-English written articles, or studies where the patient population was under 18 years of age (Figure 1).

Figure 1. Schematic representation of the search method.

Following the search from different databases, a total of 126 articles was retrieved, of which 12 were duplicates and another 69 articles did not meet the inclusion criteria. Studies excluded were those that had patient populations originating outside the MENA region, review articles, non-English written articles, or studies where the patient population was under 18 years of age.

Forty-five studies met the inclusion criteria and are reported in the current study (Table 1). After analysing the 45 studies, 24 were performed in Iran, 14 in Turkey, 4 in Saudi Arabia, 2 from Tunisia and 1 in Iraq. Represented in Figure 2 is the distribution of MENA studies according to the genetic abnormalities. From our findings, the following are the common genetic abnormalities found in the MENA region: (i) Y chromosome microdeletion, (ii) deletion or gene mutation, (iii) gene polymorphism or copy number variations, (iv) chromosomal disorders, and (v) mitochondrial mutation. The findings will be discussed under these headings.

Figure 2. Distribution of MENA studies according to the genetic alteration the genetic alteration.

From our findings, the following are the common genetic abnormalities found in the MENA region: (i) Y chromosome microdeletion, (ii) deletion or gene mutation, (iii) gene polymorphism or copy number variations, (iv) chromosomal disorders, and (v) mitochondrial mutation.

Y chromone microdeletion

One of the most common genetic aberrations contributing to infertility is Y chromosome microdeletion. The Y chromosome is one of two sex chromosomes available within the human genome. Structurally, the Y chromosome is composed of a short arm (Yp) and a long arm (Yq) (Ferlin et al. 2006, Gurkan et al. 2013). The long arm of the Y chromosome is made of repetitive elements that leave individuals at a high risk of internal recombination and segmental deletions. The function of the Y chromosome is to drive gonadal differentiation and develop the male phenotype (Gurkan et al. 2013).

Y chromosomal microdeletions can arise in the P or Q arm of the chromosome. If it arises in the p arm, it directly disturbs the differentiation of the testis. Y chromosome microdeletions in the AZF region of the q arm may lead to infertility. The AZF region is made up of multiple genomic loci, including AZFa, AZFb, AZFc, AZFd. These regions are believed to be responsible for spermatogenesis (Gurkan et al. 2013).

Located in the AZFa region is Ubiquitin specific peptidase 9 Y linked (USP9Y), which plays an important role in male reproductive development and spermatogenesis (Colaco and Modi 2018), as studies have shown its absence in infertile men whilst also noting its lack even in normal sperm count fertile men (Colaco and Modi 2018). Dead Box RNA Helicases, Box 3, Y linked (DBY), another functional gene in the AZFa region, encodes an ATP-dependent DEAD-box RNA helicase that is only expressed in germ cells. It has a homologue on the X chromosome (DBX) with 95% similarity, with the former playing a role limited to pre-meiotic male germ cells and the latter on post-meiotic spermatids. Males who did not have the DBY gene exhibited either Sertoli Cell only Syndrome (SCOS) or severe hypospermatogenesis, suggesting the gene’s importance in spermatogenesis (Foresta et al. 2000, Stanton et al. 2012). The functional genes seen in AZFb include Ribosomal protein S4, Y linked (RPS4Y2), which is expressed in the testis and prostate (Stahl et al. 2012). It plays a vital role in post-transcriptional regulation of the spermatogenic process. The Heat Shock Transcription Factor, Y linked (HSFY), exists as two coding copies in AZFb, HSFY1 and HSFY2. HSFY is predominantly present in the nuclei of round spermatids and is also associated with spermatogenesis (Stahl et al. 2012). One of the most important genes located in the AZFb region with 6 copies is the Ribonucleic Acid Binding Motif, Y linked (RBMY) and it is responsible for the regulation of alternating splicing during spermatogenesis (Poongothai et al. 2009). Deleted in Azoospermia (DAZ) genes are located in the AZFc region and have autosomal homologues. There are palindromic duplications of DAZ. These sequences together encode an RNA-binding protein vital for spermatogenesis. Infertile males with loss of DAZ seem to be highly predisposed to azoospermia and oligozoospermia (Al-Janabi et al. 2020). Albeit that the presence of DAZ deletions in both fertile and infertile men question its importance, the former although fertile have lower sperm counts and reduced sperm motility. Basic protein Y linked 2 (BSY2) is expressed in the testis and it is implicated in the process of male germ cell development. This gene is hypothesized to be involved in the cytoskeletal regulation of spermatogenesis. Testis specific protein is a multicopy gene that is only expressed in the testis and is possibly responsible for germ cell proliferation (Ceylan et al. 2009, Dhanoa et al. 2016).

Genetic mutations

Genes control a variety of physiological processes, including reproductive developments. Spermatogonial stem cells must undergo a variety of processes before becoming fully matured spermatozoa; these phases are controlled by genes. Any variation in genes that contribute to sperm maturation may lead to infertility.

Genetic abnormalities account for 15-30% of infertility cases worldwide (Kovac and Alexander W. Pastuszak 2014), hence, identifying and understanding the various genetic mutations is vital. It is important to recognize the genetic basis of infertility to provide better care, as well as an improved prognosis to infertile couples. Several studies have shown how the variation in essential spermatogenesis specific genes led to the impairment of this process and ultimately male infertility (Avenarius et al. 2009, Shahid et al. 2010, Etem et al. 2010, Asadpor et al. 2013, Jamshidi et al. 2014, Alazami et al. 2014, Shaveisi-Zadeh et al. 2017, Al-Agha et al. 2018, Monsef et al. 2018, Akbari et al. 2019, Askari, Karamzadeh, et al. 2019, Askari, Kordi-Tamandani, et al. 2019, Hojati et al. 2019, Alimohammadi et al. 2020). This section will briefly describe some genes that the deletion or mutation thereof led to impaired male fertility.

Single nucleotide polymorphisms (SNPs)

Single nucleotide polymorphisms (SNPs) are the replacement of a nucleotide at a single position within the genome, giving rise to a new allele. A SNP may occur anywhere along the genome, affecting genetic integrity. If it occurs on the sex chromosomes it may hinder the maturation of sperm, leading to infertility (Ben khelifa et al. 2011, Gurkan et al. 2013, Haji Ebrahim Zargar et al. 2015, Yousefi et al. 2015, Najafipour et al. 2016, Kamaliyan et al. 2018, Nasirshalal et al. 2020, Pashaei et al. 2020). Understanding the specifics of where the gene is mutated, and how it can lead to male infertility is vital in the treatment and management plan of the patient.

Chromosomal disorders

The implication of chromosomal disorders on male infertility including numerical, structural, replacement, inversion, insertion and translocational chromosomal abnormalities have been explored and documented (Balkan et al. 2008, Akgul et al. 2009, Alhalabi et al. 2013), especially for the numerical and structural chromosome disorders (Balkan et al. 2008, Alhalabi et al. 2013).

Mitochondrial mutation

The mitochondrion is a double-membrane organelle that generates about 90% of cell energy in the form of adenosine triphosphate by oxidative phosphorylation reaction in mammalian cells. Mitochondria play a crucial role in a series of signal pathways, including tricarboxylic acid cycle, the β-oxidation of fatty acids, regulation of intrinsic apoptosis, and participating in the cell cycle (Arakaki et al. 2006, Finkel and Hwang 2009, Yan et al. 2019). In contrast to the other organelles in a mammalian cell, mitochondria have DNA, known as mitochondrial DNA (mtDNA), which encodes a series of crucial proteins for mitochondrial respiration. The mtDNA is particularly susceptible to certain stress-induced damages due to a lack of histones in the structure and effective repair mechanisms (Kujoth et al. 2005) mtDNA mutation caused by stress-induced damage is highly associated with various human diseases, including male infertility (Venkatesh et al. 2009).

Clinical implications

In vitro fertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI) have allowed couples with fertility problems to achieve success. The success of these procedures varies from couple to couple, due to the fact that different couples present with diverse causes of male infertility. A study by Ocak et al. explored the causes of reproductive failure in a cohort of 500 patients. They found that the causes of infertility ranged from no chromosomal variations to Y-chromosomal variation. Thus, demonstrating the importance of genetic testing before commencing assisted reproductive techniques (ART) (Ocak et al. 2014). With that being said, most patients are still willing to attempt such procedures, as these procedures present as a last hope option.

Y chromosome microdeletion is one of the most common causes of male infertility; many males who suffer from Y chromosome microdeletion undergo IVF and ICSI. Screening for Y chromosome microdeletion has become a standard practice before partaking in either IVF or ICSI, as they may offer a prognostic value, predicting the potential success for ART (Sadeghi-Nejad and Farrokhi 2007). Knowing the type of Y chromosome microdeletion may help offer some prognostic value, as not all types of microdeletions yield the same results with ART. It has been demonstrated that sperm retrieval through testicular sperm extraction was possible in patients with AZFC microdeletion but not possible in AZFA and AZFB (Krausz et al. 2000, Hopps et al. 2003). A more recent study by Abur et al. also demonstrated that ART was possible with AZFC deletion (Abur et al. 2019), marking the importance of differentiating between types of Y-chromosome microdeletion before commencing ART. Other chromosomal abnormalities may affect the success rate of ART; such an example would be 46 XX chromosomal abnormalities. Akar et al. reported that other than the clinical and laboratory findings of 46 XX chromosomal translocation, patients with such a condition may have to resort to a sperm donor as sperm retrieval is not a viable option in such a patient population (Akar et al. 2020). Furthermore, this patient population should opt for testosterone replacement therapy to be protected against the negative effects of testosterone deficiency (Akinsal et al. 2017).

Additionally, high levels of aneuploidy are positively associated with an increased level of male factor infertility (Schulte et al. 2010). As such, sperm with aneuploidy is associated with a higher rate of failure with ART (Harton and Tempest 2012). Sperm relies on energy from the mitochondria for its motility, therefore, any variation in mtDNA leads to altered motility, negatively impacting fertility outcomes. A proposed solution for such infertility is ICSI. Studies now show that although mitochondrial DNA variation has a negative impact on ICSI outcomes, it is still possible (Al Smadi et al. 2021). Sperm DNA integrity is one of the vital prognostic factors of male fertility. Anything that compromises sperm DNA can lead to infertile outcomes. The findings on IVF outcomes in patients with abnormal sperm DNA have been conflicting. Some studies state that variation in the DNA of sperm have no effect on fertility outcomes (Collins et al. 2008), while others state otherwise (Simon et al. 2017). The controversy may be due to the diversity methodological approaches. Hence, it is suggested that a standardized protocol be developed.

Upon achieving success with ART, the main concern shifts to the possible vertical transmission to the offspring. Reports have shown that microdeletions have the capability of transmitting to the offspring by ICSI (Jiang et al. 1999, Zhu et al. 2010). Unfortunately, vertical transmission of Y chromosome microdeletion have been reported to cause infertility in offspring (Kim et al. 2003, Dai et al. 2012). Studies have also shown that males with aneuploidy have a higher chance of giving birth to children with aneuploidy which can translate to a variety of health conditions (Harton and Tempest 2012). This dilemma requires the design of further prospective clinical cohort studies that will assess whether the deleted regions on the Y chromosome are amplified and whether they can cause any significant new health consequences. Investigations on the possible transmission of damaged DNA should also be developed.

Conclusion

In comparison to the data available on the global investigation of infertility, particularly male infertility, findings about this subject in the MENA region is lacking. This may be due to the poorly funded niche-specific research, or social stigmatization. Accessibility to the few studies has revealed that the prevalence of demographic male infertility in the MENA region is on the increase, which makes the investigation of the causes of male infertility important.

In addition to semen analysis derived diagnosis, studies have indicated the role of genetic abnormalities as part of the cause of male infertility. Findings from the current study showed that the prevalent genetic aberration leading to male infertility in the MENA region include Y chromosome microdeletion, the occurrence of gene polymorphism, mitochondrial microdeletion and other genetic deletions or mutations.

The study of male infertility in the MENA region should encompass the investigation of various genetic variations. Diverse clinical genetic tests should also be made available for the proper diagnosis of male infertility. This would furthermore help researchers and clinicians to develop informed treatment strategies. Additionally, before providing couples with ART options, a thorough screening should be performed, and the scope of interest of reproductive medicine physicians should as well include understanding the root cause of infertility rather than just establishing pregnancy.

Data availability

No data is associated with this article.