Fertility problems in men carrying chromosome 7 inversion: A retrospective, observational study

Abstract

Infertility is a worldwide public health issue. Fifty percent of infertile couples are male-only. A number of male infertility etiologies are significantly influenced by chromosomal abnormalities. Clinical manifestations, however, differ according to the presence of aberrant chromosomes and distinct breakpoints. The reproductive effects of inversion are evident in those who carry it. The influence of inverted carriers on male infertility may be explained by the interchromosomal effect, although further research is still needed to determine the precise mechanism. Furthermore, selecting clinical reproductive technology presents difficulties for both physician and patients. The aim of this study is to determine the clinical characteristics of 4 males who have an inversion of chromosome 7, and to investigate the connection between the breakpoints of this chromosome and male infertility. For each patient, cytogenetic and semen analyses were carried out. Using PubMed or Online Mendelian Inheritance in Man, relevant research and genes on breakpoints on chromosome 7 were found. This study includes 4 male infertile patients, all of whom had chromosome 7 inversions. 46,XY,inv(7)(p22q22), 46,XY,inv(7)(p21q11.2), 46,XY,inv(7)(p21q21), and 46,XY,inv(7)(p15q36) were the results of the cytogenetic analysis. Three cases of aberrant semen parameters were detected by semen detection. After a literature search, 21 cases of chromosome 7 inversion carriers were found. These carrier couples have varying reproductive histories. Among the 5 cases where semen parameters are available, 1 is azoospermia and 1 is oligoasthenozoospermia. Five significant genes on chromosome 7 have been linked to male infertility. Changes in semen parameters may be connected to the breakpoints 7q11, 7q21, 7q22, and 7q36. Physicians should take into account the relevant breakpoints when offering genetic counseling to patients who have chromosome 7 inversion.

1. Introduction

Fifty percent of infertile couples are male-only. Infertility is a worldwide public health issue.^[1–3] The number of cases of male infertility has been rising annually in recent years.^[4,5] Genetic factors play a crucial role in various etiologies of male infertility.^[6,7] Chromosome abnormalities are a major genetic factor that is directly associated with male infertility. The various manifestations of male carriers are azoospermia, oligozoospermia, asthenozoospermia, teratospermia, repeated spontaneous miscarriages of the spouse, and birth abnormalities in the offspring.^[8–11] Clinical characteristics can also differ according to the presence of aberrant chromosomes and distinct breakpoints.^[12–14] Because of this, genetic counseling is still challenging in clinical settings.

Carriers of chromosomal inversions clearly experience reproductive consequences.^[15] The influence of inverted carriers on male infertility may be explained by the interchromosomal effect, although further research is still needed to determine the precise mechanism. But, recent studies have shown that infertile carriers with chromosome inversions are not affected by interchromosomal effects.^[16] Moreover, inverted carriers display a variety of clinical symptoms along with different chromosomes and breakpoints. As a result, selecting clinical reproductive technology presents difficulties for both physicians and patients. Whether natural conception combined with prenatal diagnosis or assisted reproductive technology accompanying preimplantation genetic diagnosis can be a choice in fertility counseling.^[17]

The fertility issue of multiple chromosomes has been discussed. The most debated and extensively discussed link is that of chromosome 9 inversion and male infertility.^[18–21] The reproductive problems associated with male chromosome 1, 2, 6, and 10 inversion carriers have been reviewed.^[22–26] It is yet unknown, nevertheless, how the inversion of chromosome 7 and its breakpoint affect male infertility.

In order to better understand the connection between male infertility and chromosome 7 inversion breakpoints, this study looked at the clinical characteristics of 4 men who had the inversion and reviewed relevant cases reported in the literature.

2. Materials and methods

2.1. Study design and settings

An observational, retrospective study was conducted at the First Hospital of Tsinghua University and was approved by the Ethics Committee of the First Hospital of Tsinghua University. The need for informed consent was waived due to the retrospective study design of this study.

2.2. Patients

This study included 4 male carriers of chromosomal inversion. Three patients came to the hospital for a checkup due to their wives not being pregnant after many years of marriage. Another man went to the doctor because his wife had often had spontaneous abortions. A questionnaire survey was completed by each patient, covering pertinent daily behaviors, environmental data, and a thorough family medical history. With their informed agreement, all patients underwent cytogenetic and semen analysis. Their spouses were also requested to provide gynecologic histories, karyotype results, and gynecological examinations at the same time.

2.3. Semen analysis

The World Health Organization’s recommended method for semen analysis was followed, and our published literature provides a thorough description of the operating methods.^[14] For each patient, semen samples were collected following 3 to 7 days of sexual abstinence. Samples were obtained through masturbation and deposited into sterile containers. After a 30-minute liquefaction period at 37°C, semen parameters were analyzed. These parameters were detected using the computer-aided semen analysis (CASA) system (Beion S3, Shanghai Beion Medical Technology Co., Ltd, Shanghai, China). Sperm motility was evaluated in at least 200 spermatozoa by analyzing various real-time images captured by the CASA system, with each sperm cell categorized as progressive motile, non-progressive motile, or immotile. No sperm in semen was diagnosed as azoospermia. Sperm concentrations below 1 × 10⁶/mL were considered as severe oligozoospermia. Asthenospermia was identified when the percentage of sperm with progressive motility was <32%.

2.4. Cytogenetic analysis

We conducted a cytogenetic analysis using our published literature as a guide.^[14] 2 mL of peripheral blood was extracted from each patient and placed in heparin anticoagulant tubes. 1 mL of heparin-anticoagulated peripheral blood was inoculated into lymphocyte culture medium, and sterile procedures were performed during this process. The inoculated culture medium was placed in a 37°C incubator and cultured for 72 hours. Then, colchicine at a concentration of 50 μg/mL was added, and continued to culture for 1 hour. The process of chromosome harvesting included hypotonic treatment, prefixation, triple fixation, preparation of cell suspension, and droplet preparation. Then, after trypsin treatment, Giemsa staining was performed for 5 to 10 minutes, followed by rinsing with water and air drying. G-banding was performed, followed by microscopic examination, counting 20 cells per case, and analyzing 6 karyotypes. Abnormal chromosomes were described according to the International System of Nomenclature for Human Cytogenetics (ISCN, 2020).^[27]

2.5. Literature review

We searched PubMed for pertinent papers concerning the inversion of chromosome 7. Reproductive-age male cases were gathered, with instances involving women, malignancies, and prenatal diagnosis excluded. Online Mendelian Inheritance in Man (https://www.omim.org) was used to search for relevant genes on several breakpoints of chromosome 7 (7p12, 7q11, 7q21, 7q22, and 7q36) in order to examine the connection between chromosome 7 inversion and male infertility.

3. Results

Four male infertile patients who all had chromosome 7 inversions were included in this investigation. Male Case 1 was 26 years old and had a typical phenotype. His spouse experienced 3 successive unplanned miscarriages. Sperm parameters were found to be within the usual reference value range based on the results of the semen study. 46,XY,inv(7)(p22q22) was the result of the karyotype study (Fig. 1A). Case 2 had a normal phenotypic and was 29 years old. Semen analysis revealed severe oligozoospermia. 46,XY,inv (7)(p21q11.2) was the karyotype (Fig. 1B). Case 3 had a 28-year-old male patient with asthenospermia and a normal phenotype. 46,XY,inv (7)(p21q21) was the karyotype (Fig. 1C). The individual in Case 4 was 32 years old and had a typical phenotype. According to the results of the semen study, the patient had azoospermia. His karyotype, according to cytogenetic analysis, was 46,XY,inv(7)(p15q36) (Fig. 1D). Results from the spouses’ routine clinical genetic and gynecological examinations revealed no unusual changes.

Figure 1.

G-banding karyotypes of the 4 patients in this study.

By doing a literature search, 21 male carriers of the chromosome 7 inversion were found, allowing us to investigate the connection between this mutation and male infertility. Table 1 displays the clinical characteristics that were gathered for these instances. There were only 2 cases discovered: 1 with azoospermia and 1 with oligozoospermia. These 2 cases have karyotypes 46,XY,inv(7)(q22q31) and 46,XY inv(7)(q11.2; q22),respectively. The reproductive histories of these carrier spouses differed throughout the 21 cases. Seven of the cases had infertility, while the remaining ones had stillbirths, deformed children, or recurrent spontaneous miscarriages.

Table 1.

Clinical features of inversion carriers involving chromosome 7.

Case	Karyotype	Seminal parameters	Reproductive history of the couple	Reference
1	inv(7)(p22q22)	N/A	Miscarriage	Demirhan et al[28]
2	inv(7)(p22q32)	N/A	A miscarriage	Winsor et al[29]
3	inv(7)(p21q34)	N/A	Reproductive failure	Gada Saxena et al[30]
4	inv(7)(p15q21)	N/A	Recurrent abortion	Portnoï et al[31]
5	inv(7)(p15q22)	N/A	Paternally inherited, 2 miscarriages	Dong et al[32]
6	inv(7)(p15q11.2)	N/A	Infertility	Yuan et al[33]
7	inv(7)(p13q21.1)	N/A	Infertility, PGT	Young et al[16]
8	inv(7)(p13q36)	Normozoospermia	Five first-trimester spontaneous abortions	Navarro et al[34]
9	inv(7)(p13q36)	N/A	Stillbirth	Li et al[35]
10	inv(7)(p13q36)	N/A	Recurrent spontaneous abortion	Zhang et al[36]
11	inv(7)(p12q32)	N/A	N/A	Rouen et al[37]
12	inv(7)(p11q21.1)	N/A	A malformation child	Vorsanova et al[38]
13	inv(7)(q11q22)	N/A	Fetus carrying the same inversion	Martin[39]
14	inv(7)(q11q36)	N/A	Recurrent spontaneous abortion	Tunç et al[40]
15	inv(7)(p11.2q11.2)	N/A	Infertility, ART	Jesus et al[41]
16	inv(7)(q11.2q22)	N/A	Recurrent fetal wastage	Fryns and Van Buggenhout[42]
17	inv(7) (q11.2;q22)	Oligoasthenozoospermia	Paternal	Peschka et al[43]
18	inv(7)(q22q34)	N/A	Infertility	Li et al[44]
19	inv(7)(q22q34)	Normozoospermia	Infertility, paternally inherited	Faed et al[45]
20	inv(7)(q22q31)	Azoospermia	Infertility	Ichioka et al[46]
21	inv(7)(q22.1q31.2)	Normozoospermia	Infertility, paternally inherited	Matsuda et al[47]

ART = assisted reproductive technology, N/A = not applicable, PGT = preimplantation genetic testing.

Relevant genes at these breakpoints were examined in order to explore more about the connection between male infertility and these chromosome 7 breakpoints related to inversion (Table 2). There were 5 significant genes linked to male infertility identified. The ZPBP gene is associated with globozoospermia and is found on chromosome 7p12. Extreme oligozoospermia is tightly associated with the 7q11 gene FKBP6. The CFAP69 gene is associated with asthenospermia and is found on chromosome 7q21. The genes STAG3 and XRCC2, which are strongly associated with azoospermia, are found on chromosomes 7q22 and 7q36, respectively.

Table 2.

Important genes and its functions related to the breakpoints on chromosome 7.

Breakpoint	Gene	Full name of gene	Loci	Expression or Function	Clinical findings
7p12	ZPBP (608,498)	Zona pellucida-binding protein	7p12.2	Localization of ZPBP to the acrosome in human spermatids	Globozoospermia
7q11	FKBP6 (604,839)	Fk506-binding protein 6	7q11.23	Exceptionally high expression in testis	Extreme oligozoospermia
7q21	CFAP69 (617,949)	Cilia- and flagella- associated protein 69	7q21.13	CFAP69 localized to the midpiece of human sperm flagellum	Asthenospermia
7q22	STAG3 (608,489)	Stromal antigen 3	7q22.1	STAG3 is essential for proper pairing and segregation of chromosomes during meiosis	Nonobstructive azoospermia
7q36	XRCC2 (600,375)	X-ray repair cross complementing 2	7q36.1	XRCC2 involved in homologous recombination repair of DNA damage	Azoospermia

N/A = not applicable.

4. Discussion

Worldwide, cytogenetic technology is still a highly effective and reasonably priced clinical diagnostic method.^[48,49] Before introducing infertile males to therapy, this technique is advised.^[50] The carrier’s fertility is thought to be impacted by the chromosomes and breakpoints implicated in the rearrangement.^[51] A chromosomal breakpoint may indicate an imbalance in the genome or result in modifications to the gene dosage, both of which might impact spermatogenesis.^[52] Male infertility has been linked to many chromosomal inversion breakpoints, however, it is yet unknown how chromosome 7 inversion carriers will fare in terms of fertility.

On chromosome 7, there are several significant genes whose expressed proteins are linked to different human disorders. For instance, it is previously known that male infertility is linked to the CFTR gene. The gene, which is located on chromosome 7, is necessary for the cystic fibrosis transmembrane conductance regulator protein to be produced and transported in its intact and functional form.^[53] PDE1C is abundantly expressed in the human heart and some areas of the brain and is in charge of hydrolyzing the second messenger chemicals cyclic adenosine monophosphate and cyclic guanosinc monophosphate. The inversion of chromosome 7 disrupts PDE1C, leading to developmental delay in the carrier.^[54] Four male infertile patients who all have chromosome 7 inversions are reported in this study. Three of these 4 patients had aberrant semen parameters. Chromosome 7 inversion was found in a patient with azoospermia according to Ichioka et al.^[46] This led to the hypothesis that chromosomes 7q22-31 could be the cause of the patient’s defective spermatogenesis. Thus, more study is required to determine whether chromosome 7 inversion and male infertility are related.

We discovered that these carriers had a variety of clinical characteristics by compiling the instances that have been described in the literature. Seven of the cases had infertility,^{[16,33,41,44–47]} while the remaining ones included stillbirth, recurrent spontaneous miscarriages, or children with deformities.^{[28–32,34–40,42,43]} Regretfully, the semen quality in most cases is not available (Table 1). One is azoospermia and 1 is oligoasthenozoospermia. There were only 2 cases discovered: 1 with azoospermia and 1 with oligozoospermia. The karyotypes of the 2 patients are linked to the 7q22 chromosomal breakpoint. Case 1 in this study had a karyotype that includes 7q22, but the semen values are within normal limits. Therefore, it remains challenging to provide genetic counseling to patients based only on chromosomal inversion breakpoints.

Relevant genes at some breakpoints of chromosome 7 were summarized (Table 2). There are some genes on chromosomes 7p12, 7q11, 7q21, 7q22, and 7q36 that correspond to ZPBP, FKBP6, CFAP69, STAG3, and XRCC2, respectively. ZPBP protein plays an early structural role during spermiogenesis.^[55] According to Oud et al,^[56] a Moroccan male patient had homozygosity for a nonsense mutation in the ZPBP gene, which resulted in globozoospermia. Male fertility and meiotic homologous chromosomal pairing are significantly impacted by the FKBP6 gene.^[57] According to Wyrwoll et al,^[58] 3 male patients with homozygous mutations in the FKBP6 gene experience severe oligozoospermia. The construction and stability of flagella in sperm cells depend on the CFAP69 protein.^[59] According to He et al,^[60] asthenospermia is linked to the CFAP69 gene mutation because of several sperm flagella morphological defects. For the chromosomes to properly pair and segregate during meiosis, the STAG3 protein is necessary.^[61] Meiotic arrest renders a male German carrier of a compound heterozygous condition in the STAG3 gene infertile.^[62] The RAD51 gene family, which includes the XRCC2 gene, codes for proteins that aid in the repair of DNA damage through homologous recombination.^[63] According to Yang et al,^[64] azoospermia resulting from meiotic arrest was seen in 2 male carriers who possessed homozygous mutations in the XRCC2 gene. Male infertility may result from structural chromosomal abnormalities that impair the activity of variant genes.^[65] We hypothesize that the disruption of associated genes at these breakpoints may be connected to the variations in semen parameters seen in the 3 patients in our investigation. Undoubtedly, additional clinical case data needs to be gathered.

The limitation of this study is that the number of cases is small, and semen parameters of the retrieved cases in the literature are mostly not applicable. No molecular genetics experiments were conducted.

5. Conclusions

In conclusion, this study discussed the reproductive problems of these carriers while reporting 4 cases and recovering 21 males with chromosome 7 inversion. Breakpoints 7q11, 7q21, 7q22, and 7q36 have been found to have variable final reproductive results, which may be related to variations in semen characteristics. Physicians should take into account the relevant breakpoints when offering genetic counseling to patients who have chromosomal 7 inversion.

Author contributions

Conceptualization: Zhiqiang Song, Ranwei Li.

Data curation: Zhiqiang Song, Jianchen Wu.

Investigation: Qiuyu Wang, Ranwei Li.

Writing – original draft: Zhiqiang Song.

Writing – review & editing: Ranwei Li.