Genetic factors are one of the critical factors leading to male infertility, including chromosome karyotype abnormality, gene copy number variation, single gene mutation, and Y chromosome microdeletion, among which the most common are karyotype abnormality and Y chromosome microdeletion [12]. The findings of several studies indicate that approximately 8–10% of infertile males in China exhibit Y chromosome microdeletions [13,14,15,16]. However, no studies with a substantial sample size have been published in the southernmost region of China.

In this study, we evaluated the prevalence of Y chromosome microdeletions in male infertility among the Hainan population, China’s sole tropical island province. A total of 897 infertile men from Hainan Province, diagnosed with oligozoospermia or azoospermia and excluding chromosomal abnormalities, were included in the study. Y chromosome microdeletions were detected in 64 patients, with an overall incidence of 7.13% (64/897). The rate of Y chromosome microdeletion in infertile males in Hainan was generally lower than in other regions of China [8] and the world, including Iraqi (47.8%) [17], Morocco (18.82%) [18], India (10.02%) [8] and Korea (10.93%) [19] but higher than in Turkey (6.82%) [20] (Table 4). It may be a unique group characteristic of the Hainan population in China. The deletion of the AZF region is typically regarded as Y chromosome microdeletion and is being gradually considered by specialists. The incidence of Y chromosome microdeletion in infertile men varies significantly among different laboratories due to the utilization of diverse population methodologies and STSs [21,22,23]. Therefore, it is imperative to integrate multiple influencing factors to comprehensively describe and elucidate the occurrence of Y chromosome microdeletions across diverse regions.

The AZF region of the Y chromosome is further divided into three subregions: AZFa, AZFb, and AZFc. Regarding localization, the AZFa region is situated at the proximal end of the long arm of the Y chromosome, closest to the centromere. The AZFc region is located at the distal end, while the AZFb region lies between these two subregions (Fig. 1). Additionally, specific fragments within the AZFb region overlap with those in the AZFc region [24]. The deletion of distinct subregions results in varying sterility phenotypes. The present study investigated the effects of single and combined subregion deletion in infertile males. We found that the most common type of AZF microdeletion in infertile men in Hainan Province was AZFc deletion (4.91%), and there was a significant difference in incidence between oligozoospermia and azoospermia, i.e., infertile men with AZFc deletion were more frequently found to have oligozoospermia. The previous data indicated that the highest incidence of AZF microdeletion in infertile men was AZFc deletion [18, 20, 25,26,27]. However, some studies have reported different results. The recent study revealed a higher prevalence of AZFa subregion deletion in microdeletion infertile men, significantly correlated with the oligozoospermia phenotype [28]. Although much of the present data still suggests that AZFa deletions are not the most common type in male infertility patients compared with other kinds of AZF deletion [29, 30], it has been reported that AZFa deletion can lead to the most severe phenotype, which in the case of complete AZFa region deletion occurs as Sertoli Cell Only Syndrome (SCOS), in which there are no sperm cells at all in the testicular convoluted tubules, and only Sertoli cells are seen [31,32,33]. The reported prevalence of SCOS in azoospermia patients ranges from 26.3–57.8% [34, 35]. The etiologies of human SCOS are diverse, encompassing Y chromosome microdeletions, cryptorchidism, chromosomal disorders, cytotoxic drugs, radiation exposure, and viral infections [36].

In our study, we identified four infertility patients with AZFa deletions. Two patients exhibited complete AZFa deletions (i.e., deletions at both sY84 and sY86 STS sites) and consistently presented with azoospermia. The other two patients showed deletions only at the sY86 STS site, without the sY84 deletion, which was considered partial AZFa deletion and exhibited oligozoospermia. A recent study reported that approximately 61.3% of 75 males with severe oligozoospermia or azoospermia had AZFa region deletions, confirming a significant association between partial or complete AZFa deletions and male infertility and spermatogenic failure, with partial AZFa deletions occurring more frequently than complete deletions [37]. However, another study reported that microdeletions in the AZFa region are associated with diverse phenotypes, including azoospermia, oligozoospermia, and normozoospermia [38]. Patients with complete AZFa deletions and Sertoli cell-only syndrome (SCOS) cannot retrieve sperm via microdissection testicular sperm extraction (mTESE) for assisted reproductive techniques such as intracytoplasmic sperm injection (ICSI). Thus, mTESE is not recommended clinically [39]. Instead, donor sperm should be considered for assisted reproductive treatments of these patients. However, for patients with partial deletions who may present with oligozoospermia, mTESE followed by ICSI is a viable option. Still, the patient must be fully informed of the potential of inheriting the same deletion in the male of his offspring.

This study found two types of co-deletion of AZF subregions, AZFb + c and AZFa + b + c. The incidence of AZFb + c subregion combined deletion is higher in infertile men, followed by AZFa + b + c deletion. These two types of combined microdeletion were only detected in patients with azoospermia, not in oligozoospermia, consistent with previous reports [19]. It was shown that AZFb + c subregion deletion may be most closely related to the azoospermia phenotype. Azoospermia and oligozoospermia patients should perform Y chromosome deletion screening before testicular sperm extraction (TESE) or intracytoplasmic sperm injection (ICSI). If they are found in the region of AZFa, AZFb + c, or AZFa + b + c complete deletion, TESE should not be recommended. If these partial deletion patients have a strong desire for fertility, can we perform mTESE to win some opportunities for patients? This question is worth discussing and analyzing. Hainan Island has more than 30 ethnic groups, including Han, Li, Miao, and Hui, among which ethnic minorities account for 18.02% of the province’s population. Minority groups have more traditional ideas and a strong desire to have children. With fully informed consent, can we take some proactive ways to assist sperm retrieval in patients with AZF deletion? We need more scientific evidence and support.

The hypothalamic-pituitary-testicular axis mainly regulates testicular spermatogenesis and changes in reproductive hormones will affect male reproductive function [40]. This study further analyzed the sex hormone levels of infertile men with AZF microdeletion in Hainan. It aimed to explore the relationship between sex hormone levels and different sterility phenotypes caused by AZF microdeletion. We found a significant increase in serum FSH (21.63 ± 2.01 U/L vs. 10.15 ± 0.96 U/L) and LH (8.96 ± 0.90 U/L vs. 4.58 ± 0.42 U/L) levels in AZF microdeletion azoospermia patients compared to AZF microdeletion oligospermia patients. This finding is consistent with hormonal analysis results from the previous report [28]. Normal spermatogenesis depends on the synergistic regulation of multiple sex hormones. Elevated FSH levels suggest a decline in testicular function [41]. Previous studies have also shown that infertile patients with microdeletions have significantly higher FSH and LH levels than those without [19]. In addition, we found that compared with oligozoospermia patients, the serum PRL levels of AZF microdeletion in azoospermia men were also significantly higher. A previous study revealed that serum PRL levels were significantly elevated in patients with azoospermia compared to healthy men, while patients with oligozoospermia were in between [42]. In the male reproductive system, the prominent role of PRL is to regulate the FSH receptor on the supporting cells and the LH receptor on the testicular interstitial cells to affect the reproductive function of the testis [43]. At the same time, serum PRL can inhibit the release of GnRH and decrease the secretion of both FSH and LH [44]. FSH, LH, and PRL levels may have specific diagnostic and predictive values for infertile men with AZF microdeletion.