The successful application of current assisted reproductive technologies used for infertile couples requires a precise understanding of the involved genetic factors as one of the important causes of male factor infertility [22]. Therefore, in this study, some common genetic risk factors such as chromosomal abnormalities, Y chromosome microdeletions, CFTR gene mutations, and length of the CAG repeat in the N-terminal transactivation domain of the AR gene in severe oligozoosperimc Iranian men were investigated and compared with fertile men as a control group.
We found chromosomal abnormality at a rate of 4% (8 individuals) of severe oligozoospermic men which is consistent with previous studies reporting the range of occurred abnormalities between 2% -16% in infertile patients [23, 24]. Foresta et al in 2005 studied 750 oligozoospermic men and reported a frequency of 5.6% for chromosomal aberrations, and klinefelter was the most chromosomal abnormality in patients [25]. In the case of klinefelter syndrome as the most common karyotype abnormality in men with severe male factor infertility, four patients (2%) have been identified, while structural chromosomal abnormalities including robertsonian translocations, chromosomal inversions, and translocations 16;17 and 11;14, overall accounted for 2% (Table 2). Our results were consistent with the obtained data of a study on 935 infertile men whose karyotypes were evaluated and the rate of 6.9 % of chromosomal abnormalities was reported [26]. A smaller sample size, different inclusion criteria, and ethnicity may justify the slight differences in the data between the two studies. The probability of producing unbalanced genetic content gametes and abnormal sperm in men with chromosomal translocation is higher, whereas in men with robertsonian translocation a wide range of 3.4%-40% abnormal sperm have been observed [27].Previous studies have reported the frequency of Y chromosome microdeletions as the second leading cause of spermatogenic failure [28], varies from 1 to 58% across the world [29–31]. The most prevalent and frequent deletion occurs in AFZc (approximately 80%) following by those in AZFb (1–5%), AZFa (0.5-4%), and AZFbc (1–3%) [28]. The differences in patients enrollment criteria, sample size, used STS primers, ethnical and geographical and other genetic backgrounds and environmental influences may lead to variation in reported frequencies [29, 31–33].
Inconsistent with most of the previous reports in which AFZc was the most frequent Yq deletion [33–36], our data showed that deletions occurred most frequently in the AZFa sub-region (3%). While it is well documented that men with AZFc deletions and partial deletions in AZFb show different types of fertility status from normal fertility to oligozoospermia and azoospermia [37, 38]. In Kim et al study that was done in Korea, most microdeletion in severe oligozoospermia belongs to AZFc (87.1%) and then AZFb (36%)[5].Screening of Y chromosome microdeletions as a diagnostic, prognostic and preventive tool has great importance.Although the genetic correlation between CFTR gene mutations and male infertility due to CBAVD is well documented, recently, it has been found to play roles in other forms of male infertility besides the CBAVD phenotype. However, the link between the alteration of sperm parameters and CFTR seems to be weak and remains largely unknown [25, 39–41]. There is some evidence about the involvement of CFTR protein in reducing the cytoplasmic volume of sperm during spermiogenesis that is derived from a study on rat testicular tissue in which CFTR mRNA restriction to pre-meiotic round spermatids and principle cells, covering the primary part of the human and rodent epididymis, was observed [42].However, different studies on the frequency of CFTR mutations in infertile males without CBAVD have been reported contradictory results, while in some cohorts it was found that the elevation of CFTR mutation rate is associated with reduced sperm quality [43], male idiopathic infertility [44] and cryptozoospermia [45]. In contrast, others detected no increase in CFTR mutation frequency in males with non-obstructive azoospermia or oligoasthenoteratozoospermia [40, 46]. Therefore, the necessity of CFTR mutations screening in infertile men before intracytoplasmic sperm injection (ICSI) for example, has not been yet fully defined. In the present study, the total frequency of CFTR mutations was 8%, which is in agreement with a study on the male of the German population with reduced sperm quality who were evaluated in the case of CFTR mutation frequency. In Schulz et al study 7.69% of patients with severe oligozoospermia had a single CFTR mutation [47]. It should be noted that other studies have been reported no difference between the two groups in the case of CFTR variants between Italian people cases and controls [16, 25].Regarding androgen receptor-CAG trinucleotide repeat, our findings revealed the association between the increase in CAG-repeat expansion and the risk of severe oligozoospermia in men. There is not any standard relationship between CAG-repeat length and the risk of male infertility due to previous reports [48–50]. The correlation between CAG repeat length and Kennedy’s disease has been reported [51–53]. While this gene is located on the X chromosome, applying ICSI to treat patients with severe oligozoospermia may raise the potential risk of Kennedy disease in 2 generations (54). Also, it has been reported that AR binding activity in infertile male is decreased [55–57]. The mechanism by which CAG repeat length may affect fertility is still unknown. But in studies that have investigated the role of AR-CAG repeats in some diseases, three pathogenic mechanisms including loss of protein function, the gain of protein function, and the gain of function of RNA containing CUG repeats are suggested [58). To find the exact role of the mentioned mechanisms in male infertility future studies are needed. Komori et al reported that mean of CAG repeat in oligozoospermic men was 21.4 and in the control group was 21.2, so their study was inconsistent with our data[59]. In the current study the difference between two groups was significantly and the mean CAG repeat in the case and control group was 25.09 and 23.16 respectively. Our data were consistent with Patrizio et al study that reported CAG- repeat length in oligozoospermic men was 25.04 and in fertile men was 22[54]. In Mobasseri et al study in 2018, there was no significant difference between the two groups (Case 18.34 and control 17.53 CAG repeat length) so inconsistent with our study [22].It is necessary for couples with chromosomal structural abnormalities to have genetic counseling and apply a preimplantation genetic diagnosis test. Unfortunately, we did not assay the abnormal sperm ratio in men with chromosomal abnormalities in comparison with those without and this could be considered as the main limitation of our study.