Association of the MTHFR A1298C variant with unexplained severe male infertility

MTHFR C677T、MTHFR A1298C、MTRR A66G and MTR A2756G polymorphisms and male infertility risk: a systematic review and meta-analysis

BACKGROUND

Epidemiological studies have reported that polymorphisms of folate-metabolizing genes have a significant impact on male infertility. However, the results of published studies have come to different conclusions.

OBJECTIVE

To determine an association between folate-metabolizing gene polymorphisms and the risk of male infertility.

METHODS

The meta-analysis was conducted according to the PRISMA 2020 statement. The protocol was registered with PROSPERO (CRD42023412251). Studies were searched from PubMed, Google Scholar, Embase, Scopus, and the Cochrane Library up to 24st October2023. Articles that satisfied the inclusion criteria were evaluated for their quality using the Newcastle-Ottawa Scale. Data were extracted from the eligible studies and were analyzed for pooled up odds ratio (OR) with 95% confidence interval (CI). Meta-analysis was conducted using STATA 12.

RESULTS

Forty-six case-control studies were included in the meta-analysis which comprised 20,639 participants. The pooled analysis revealed that the MTHFR C677T polymorphism was significantly associated with male infertility and abnormospermia.Three-fifths of the model showed there was a significant association between the MTR A2756G polymorphism and male infertility. Both MTHFR A1298C and MTRR A66G polymorphisms were not significantly associated with male fertility. Furthermore, subgroup analysis revealed a significant association between the MTHFR C677T polymorphism and male fertility in Asian countries.

CONCLUSION

This meta-analysis suggests that the MTHFR C677T and MTR A2756G polymorphisms may be a potential risk factor for male infertility.

Association between methylenetetrahydrofolate reductase C677T polymorphisms and male oligozoospermia, asthenozoospermia or oligoasthenozoospermia: a case-control study

Mutation of methylenetetrahydrofolate reductase (MTHFR) C677T leads to the decrease of folate utilization and the impairment of spermatogenesis. This study attempts to investigate the association between MTHFR C677T polymorphisms and nonobstructive oligozoospermia, asthenozoospermia or oligoasthenozoospermia in the Chinese population. The study cohort comprised 189 patients diagnosed with oligozoospermia, asthenozoospermia or oligoasthenozoospermia, and 626 controls based on clinical examinations. The MTHFR c.677 genotype of all subjects was determined by fluorescence staining in situ hybridization and the significance of different genotype frequencies was further analyzed by Chi-square test. The results showed that the frequency of MTHFR 677 CT genotype in the oligozoospermia, asthenozoospermia and oligoasthenozoospermia group was 33.3%, 38.3% and 44.0% respectively, whereas it was 47.3% in the control group. The P value of Chi-square test was 0.070, 0.103 and 0.654, respectively. The frequency of MTHFR 677 TT genotype in the oligozoospermia, asthenozoospermia and oligoasthenozoospermia group was 31.1%, 11.7% and 18.0% respectively, while that in the control group was 19.5%. The P value of Chi-square test was 0.061, 0.070 and 0.066, respectively. Collectively, there is a weak association between MTHFR C677T polymorphisms and oligozoospermia, asthenozoospermia or oligoasthenozoospermia within the current Chinese population cohort.

Correlation of MTHFR C677T Polymorphism with Male Infertility among Indian Population: Case-Control Study

This case-control study investigated the correlation between male infertility in India and the methylenetetrahydrofolate reductase (MTHFR) C677T variant. Infertile males were utilized as the case group in the study, whereas fertile individuals served as the control group. The C677T polymorphism was genotyped using PCR-RFLP analysis (polymerase chain reaction-restriction fragment length polymorphism). The Chi-square test and odds ratio calculation were implemented in the statistical analysis method for assessing the correlation between the C677T mutation and infertility. The results of this study revealed that the case group (9.4%) had a substantially greater prevalence of the C677T variation than the control group (1.6%). The C677T variation is significantly associated with male infertility by the Chi-square test (P value: 0.006). According to these results, the MTHFR gene›s C677T variation may increase the incidence of male infertility in the Indian population. Additional evaluations were also conducted to investigate the association between the C677T variation and particular infertility indicators. The C677T variation has been demonstrated to have been significantly correlated with a low or missing sperm count (p 0.05). These findings highlight the potential function of the MTHFR gene in reproductive health and advance our understanding of the genetic underpinnings of male infertility. It is encouraged to investigate the underlying mechanisms and additional investigation of the underlying mechanisms and to support the creation of individualized approaches to diagnosing and managing male infertility.

More evidence for widespread antagonistic pleiotropy in polymorphic disease alleles

Introduction

Many loci segregate alleles classified as "genetic diseases" due to their deleterious effects on health. However, some disease alleles have been reported to show beneficial effects under certain conditions or in certain populations. The beneficial effects of these antagonistically pleiotropic alleles may explain their continued prevalence, but the degree to which antagonistic pleiotropy is common or rare is unresolved. We surveyed the medical literature to identify examples of antagonistic pleiotropy to help determine whether antagonistic pleiotropy appears to be rare or common.

Results

We identified ten examples of loci with polymorphisms for which the presence of antagonistic pleiotropy is well supported by detailed genetic or epidemiological information in humans. One additional locus was identified for which the supporting evidence comes from animal studies. These examples complement over 20 others reported in other reviews.

Discussion

The existence of more than 30 identified antagonistically pleiotropic human disease alleles suggests that this phenomenon may be widespread. This poses important implications for both our understanding of human evolutionary genetics and our approaches to clinical treatment and disease prevention, especially therapies based on genetic modification.

Variations in folate prescriptions for patients with the MTHFR genetic polymorphisms: A case series study

Background

Over 48.5 million couples are reported with infertility worldwide. Health policy recommends folic acid in women of childbearing age, particularly in preconception and pregnancy which results in women purchasing over-the-counter prenatal multivitamins containing folic acid through pharmacies and other retail outlets. Emerging studies are investigating whether other forms of supplemental folate are more suitable, particularly for those with methylenetetrahydrofolate reductase (MTHFR) polymorphisms. This case series aimed to document variations in forms and dosage of folate prescribed by Australian practitioners to patients with diagnosed infertility and MTHFR polymorphisms.

Methods

Australian practitioners were invited to complete a retrospective case report form for patients that presented with unexplained infertility. This case report form documented the form and dose of folate that practitioners were prescribing to their infertility patient with MTHFR polymorphisms, together with their fertility history.

Results

Six practitioners submitted case information for 12 patients with diagnosed infertility and MTHFR polymorphisms. All patients had been advised by their practitioner to remove folic acid in supplemental form and were prescribed 5-methyltetrahydrofolate (5-MTHF) or a combination of 5-MTHF and folinic acid, at higher doses than the Australian recommended dose (mean daily maximum prescribed dose: 2325μg). Eleven patients conceived within the treatment period (average treatment of one year) and ten were reported as having a live birth.

Conclusion

This case series has highlighted clinical practices that vary from the recommendations by Australian policy. Further research is required to verify the clinical importance of variations in folate prescriptions for women with MTHFR polymorphisms and how folate recommendations may need to change depending on these polymorphisms. This has direct relevance to those prescribing at the pharmacy and retail level, specifically pharmacists and pharmacy assistants.

Women Taking a Folic Acid Supplement in Countries with Mandatory Food Fortification Programs May Be Exceeding the Upper Tolerable Limit of Folic Acid: A Systematic Review

Background: In preconception and pregnancy, women are encouraged to take folic acid-based supplements over and above food intake. The upper tolerable limit of folic acid is 1000 mcg per day; however, this level was determined to avoid masking a vitamin B12 deficiency and not based on folic acid bioavailability and metabolism. This review’s aim is to assess the total all-source intake of folate in women of childbearing age and in pregnancy in high-income countries with folate food fortification programs. Methods: A systematic search was conducted in five databases to find studies published since 1998 that reported folate and folic acid intake in countries with a mandatory fortification policy. Results: Women of childbearing age do not receive sufficient folate intake from food sources alone even when consuming fortified food products; however, almost all women taking a folic acid-based supplement exceed the upper tolerable limit of folic acid intake. Conclusions: Folic acid supplement recommendations and the upper tolerable limit of 1000 mcg set by policy makers warrant careful review in light of potential adverse effects of exceeding the upper tolerable limit on folic acid absorption and metabolism, and subsequent impacts on women’s health during their childbearing years.

Association of methyltetrahydrofolate reductase gene mutation, homocysteine level with semen quality of Iraqi infertile males

Background

Infertility is very common condition and almost 50% of cases are due to male factors. Several genetic and environmental factors are responsible for the poor quality and reduced number of sperms in several cases of infertility. The present study was designed to investigate the association between semen parameters, homocysteine, and the risk of C677T polymorphism of MTHFR gene in infertile males of Iraqi population.

Methods

This Case–control study has been conducted from February 2019 to July 2021 at a molecular laboratory in the Anatomy and Histology Department/college of Medicine/University of Kufa/Najaf/Iraq. It was composed of 353 infertile male patients. They were divided into five groups: 90 azoospermic, 84 oligospermia, 64 asthenospermic, 50 oligoasthenospermic, and 65 teratospermic with an age range 20–46 years compared with 100 fertile males as control with age range 21–49 years. In order to detect homocysteine levels, we used Hcy ELISA Kit. C677T mutation of MTHFR gene was employed by PCR–RFLP technique.

Results

Our data revealed three genotypes of MTHFR C677T, 167 (47.3%) subjects had CC genotype, 116 (32.9%) subjects had CT genotype and 70 (21.1%) subjects had TT genotype. Furthermore, T allele was associated with higher risk of infertility in all patients groups for any genetic model. In total infertile subjects (codominant model: CT vs. CC, OR = 2.0, 95% C.I = 1.2–3.3, P = 0.011; TT vs. CC, OR = 4.8, 95% C.I = 3.3–8.2, P = 0.0003; dominant model: CT + TT vs. CC, OR = 2.8, 95% C.I = 1.7–4.5, P = 0.0001). Oligoasthenospermic patients associated with higher risk in CT heterozygous genotype (OR = 2.8, 95% C.I = 1.0–4.9, P = 0.03) and TT homozygous of mutant allele (OR = 6.3, 95% C.I = 1.9–9.2, P = 0.002). Homocystein level was elevated in all infertile groups when compared with control group (P < 0.01), but the elevation was marked in oligoasthenospermia group. As well as, the level of Serum Hcy exhibited the highest value in TT mutant genotype (39.7 µmol/ml) followed by CT genotype (28.5 µmol/ml) while the lowest level of Hcy recorded in CC genotype (14.6 µmol/ml) for oligoasthenospermia group.

Conclusions

By relating the MTHFR C677T gene mutation with a higher homocystein level, the results showed that Iraqi males with this mutation are more likely to suffer from infertility.

Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and male infertility risk: An updated meta-analysis

BACKGROUND

18 previous meta-analyses have been published on the methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms with male infertility risk. However, results of the previous meta-analyses were still inconsistent. Moreover, their meta-analyses did not assess false-positive report probabilities except one study. Furthermore, many new studies have been published, and therefore an updated meta-analysis and re-analysis of systematic previous meta-analyses were performed to further explore these issues.

OBJECTIVES

To determine the association between MTHFR C677T and A1298C polymorphisms and male infertility risk.

METHODS

Crude odds ratios and their 95% confidence intervals were used to assess the association between MTHFR C677T and A1298C polymorphisms and male infertility risk. We used the Bayesian false discovery probability (BFDP) to assess the credibility of statistically significant associations.

RESULTS

Fifty-nine studies were included concerning the MTHFR C677T and 28 studies were found on the MTHFR A1298C with male infertility risk. Overall, the MTHFR C677T was associated with increased male infertility risk in overall populations, Africans, East Asians, West Asians, South Asians, azoospermia, and Oligoasthenoteratozoospermia (OAT). In further sensitivity analysis and BFDP test, the positive results were only considered as "noteworthy" in the overall population (TT vs CC: BFDP = 0.294, CT + TT vs CC: BFDP = 0.300, T vs C: BFDP = 0.336), East Asians (TT vs CC: BFDP = 0.089, TT vs CT + CC: BFDP = 0.020, T vs C: BFDP < 0.001), West Asians (TT vs CC: BFDP = 0.584), hospital-based studies (TT vs CC: BFDP = 0.726, TT vs CT + CC: BFDP = 0.126), and OAT (TT vs CT + CC: BFDP = 0.494) for MTHFR C677T. In addition, a significantly increased male infertility risk was found in East Asians and population-based studies for MTHFR A1298C. However, we did not find that the positive results were considered as "noteworthy" in the overall and all subgroup analyses for MTHFR A1298C.

CONCLUSIONS

In summary, this study indicates that the MTHFR C677T is associated with increased male infertility risk in East Asians, West Asians, and OAT. No significant association was observed on the MTHFR A1298C with male infertility risk.

Association of the MTHFR 677C>T and 1298A>C polymorphisms and male infertility risk: a meta-analysis

BACKGROUND AND OBJECTIVES

One of the possible male sterility risk factors are polymorphisms of Methylenetetrahydrofolate reductase (MTHFR). However, the epidemiologic investigations described inconsistent results regarding MTHFR polymorphism and the risk of male infertility. For that reason, we carried out a meta-analysis of published case-control studies to re-examine the controversy.

METHODS

Electronic searches of Cochrane, EMBASE, Google Scholar, and PubMed were conducted to select eligible studies for this meta-analysis (updated to May 2019). According to our exclusion and inclusion criteria, only high-quality studies that remarked the association between MTHFR polymorphisms and male infertility risk were included. The Crude odds ratio (OR) with a confidence interval of 95% (CI) was used to assess the relationship between MTHFR polymorphism and male infertility risk.

RESULTS

Thirty-four case-control studies with 9662 cases and 9154 controls concerning 677C/T polymorphism and 22 case-control studies with 5893 cases and 6303 controls concerning 1298A/C polymorphism were recruited. Both MTHFR polymorphisms had significant associations with male infertility risk (CT + TT vs. CC: OR = 1.37, 95% CI: 1.21-1.55, P = 0.00, I² = 41.9%); (CC vs. CA + AA: OR = 0.82, 95% CI: 0.52-1.30, P = 0.04, I² = 50.1%). Further, when stratified by ethnicity, the significant association results were observed in Asians and Caucasians for 677C/T and just Asians for 1298A/C.

CONCLUSIONS

Some of MTHFR polymorphisms like MTHFR 677C > T are associated with an elevated male infertility risk. To confirm our conclusion and to provide more accurate and complete gene-environment communication with male infertility risk, more analytical studies are needed.

MTHFR polymorphisms as risk for male infertility in Pakistan and its comparison with socioeconomic status in the world

Aim: 5,10-MTHFR-single nucleotide polymorphisms are important for normal functioning of the enzyme that plays a key role in DNA synthesis, folate metabolism and methylation reactions. Methodology & results: Male infertility association of C665T and A1298C polymorphisms was explored, this topic is still debatable. Infertile men (232) and controls (114) were genotyped and statistically analyzed. Comparison of patients (6180) and controls (5744) of Caucasian populations was performed by meta-analysis. Pooled results showed A1298C minor allele and homozygous genotype to be of a significantly higher frequency in the low-income group. Increase in per capita income has shown an increasing trend in the minor allele frequency in various world populations, potentially due to dietry-folate compensation. Conclusion: A1298C seems more relevant marker than C665T for infertility association in Caucasian populations and may be addressed by improving dietary folate.

Detection of candidate nectin gene mutations in infertile men with severe teratospermia

PURPOSE

Approximately 40% of infertile men have an abnormal semen analysis, resulting from either abnormalities of sperm production (defective spermatogenesis) or sperm shape (defective spermiogenesis). This latter process is dependent upon the function of Sertoli cells, which maintain specialized junctional complexes with germ cells. Nectins, members of the immunoglobulin superfamily, participate in formation of these dynamic complexes. Male mice in which the nectin-2 or nectin-3 gene is knocked out are sterile. Their spermatozoa exhibit severe teratospermia, altered motility, and an impaired ability to fertilize eggs. We asked whether mutations in the protein coding regions of the nectin-2 (aka PVRL2) and nectin-3 (aka PVRL3) genes could be detected in men from infertile couples whose semen analysis revealed unimpaired sperm production, judged by normal sperm concentration, but severe abnormalities in sperm shape.

METHODS

Ejaculates were snap frozen in liquid nitrogen and later submitted for Sanger analysis of these two genes, to detect mutations in their protein coding regions.

RESULTS

Eighty-nine of 455 ejaculates (19.5%) met the inclusion criteria for study. Two of the 56 samples that were successfully analyzed for nectin-2 (3.6%) and one of 73 (1.3%) analyzed for nectin-3 possessed possibly damaging mutations.

CONCLUSIONS

Despite the small-scale nature of the study, at least two low-frequency deleterious variants were identified. These results suggest the need for a larger-scale study of sequence variants in the nectins in severe teratospermia.

Association of MTHFR, NFKB1, NFKBIA, DAZL and CYP1A1 gene polymorphisms with risk of idiopathic male infertility in a Han Chinese population

In this study, we investigated the association between six genetic polymorphisms (MTHFR C677T and A1298C, NFKB1 -94ins/del ATTG, NFKBIA 3'UTR A>G, DAZL A386G (T54A) and CYP1A1 T3801C) and the risk of idiopathic male infertility in a Chinese population. A case-control study comprising 1,759 idiopathic male infertile patients of Han Chinese ethnicity and 1,826 healthy fertile control individuals was carried out. Genotypes of all polymorphisms were determined via PCR-RFLP. Chi-squared test and logistic regression modeling were performed to identify the association of the polymorphisms with idiopathic male infertility. It was found that the heterozygous and variant genotypes of the following polymorphisms were significantly associated with an increased idiopathic male infertility risk: MTHFR C677T (heterozygous OR=1.266 [1.089, 1.470], P=0.002; variant OR=1.384 [1.138, 1.684], P=0.001), MTHFR A1298C (heterozygous OR=1.233 [1.071, 1.419], P=0.004; variant OR=1.564 [1.183, 2.068], P=0.002), and CYP1A1 T3801C (heterozygous OR=1.163 [1.007, 1.344], P=0.040; variant OR=1.232 [1.005, 1.510], P=0.045). When genotypes of non-significant polymorphisms were combined and analyzed, it was found that the combination between variant DD genotype of NFKB1 -94ins/del ATTG polymorphism and heterozygous AG genotype of DAZL A386G polymorphism was significantly associated with a reduced idiopathic male infertility risk (OR=0.588 [0.376, 0.919], P=0.02). In summary, we have successfully identified the association (or lack thereof) between the polymorphisms and idiopathic male infertility risk.

Association of C677T transition of the human methylenetetrahydrofolate reductase (MTHFR) gene with male infertility

The human methylenetetrahydrofolate reductase (MTHFR) gene encodes one of the key enzymes in folate metabolism. This gene is located on chromosome 1 (1p36.3), which has 12 exons. The aim of the present study was to investigate the possible association of the two (C677T and A1298C) polymorphisms of this gene with male infertility. In a case-control study, 250 blood samples were collected from IVF centres in Sari and Babol (Iran): 118 samples were from oligospermic men and 132 were from controls. Two single nucleotide polymorphisms of the MTHFR genotype were detected using polymerase chain reaction-restriction fragment length polymorphism. There was no association found between the A1298C variant and male infertility. However, carriers of the 677T allele (CT and TT genotypes) were at a higher risk of infertility than individuals with other genotypes (odds ratio 1.84; 95% confidence interval 1.11-3.04; P=0.0174). Structural analysis of human MTHFR flavoprotein showed that C677T transition played an important role in the change in affinity of the MTHFR-Flavin adenine dinucleotide binding site. Based on our results, we suggest that C677T transition in MTHFR may increase the risk of male infertility, and detection of the C677T polymorphism biomarker may be helpful in the screening of idiopathic male infertility.

Pathogenic landscape of idiopathic male infertility: new insight towards its regulatory networks

Idiopathic male infertility (IMI) affects nearly 10-15% of men in their prime reproductive age. More than 500 target genes were postulated to be associated with this disease condition through various genomic studies. The challenge is to determine the functional role of these genes and proteins that form part of a larger network leading to pathogenesis of the IMI phenotype in humans. In the current study, we have catalogued all of the genes associated with IMI from published studies, as well as looked at reactive oxygen species and antioxidant genes, the two key physiological determinants essential for normal spermatogenesis. Any imbalance in these genes through mutation, single-nucleotide polymorphisms (SNPs) or other forms could result in abnormal regulation of genes leading to infertility. SNPs catalogued in the current study, representing a third of the IMI genes, could possibly explain the various hidden factors associated with this condition. The enriched biological functions in SNPs, as well as functional analysis of IMI genes, resulted in the identification of novel gene pairs, from which we proposed new models to describe the underlying pathogenesis of this disease condition. The outcome of this study will give a new set of genes and proteins that could help explain the disease from a global perspective previously not addressed using standard approaches. Genes corresponding to proteins identified from the current study for spermatozoa and seminal plasma showed functional correlation based on their localization, which gave further confirmation of their roles in defective spermatogenesis as seen in IMI.

Association of the MTHFR C677T (rs1801133) polymorphism with idiopathic male infertility in a local Pakistani population

The present study determined an association between idiopathic sperm disorders in a local Pakistani infertile male population and the MTHFR C677T polymorphism. After ruling out non genetic factors, a total of 437 idiopathic infertile men including 57 azoospermic, 66 oligospermic, 44 asthenozoospermic, 29 teratozoospermic, 20 oligoasthenospermic and 221 infertile normospermic men were recruited. Furthermore, 218 normospermic fertile men, who had two children (or more) were included as controls. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used to determine MTHFR C677T (rs1801133) polymorphism. A significant association of the minor MTHFR 677T allele with male infertility was observed (p <0.05). In addition, men with MTHFR 677 CT and TT genotypes were at a greater risk [odds ratio (OR): 1.81, 95% confidence interval (95% CI): 1.17-2.80, p = 0.008 and OR: 9.24, 95% CI: 1.20-70.92, p = 0.032, respectively] of infertility. All the subgroups of male infertility (azoospermic, oligospermic, asthenospermic, oligoasthenoteratospermic (OAT) and normospermic infertile) had significantly (p <0.05) higher frequencies of CT and TT genotypes when compared to fertile men. The combined genotypes (CT + TT) were also found significantly (OR: 2.01, 95% CI: 1.31-3.08, p <0.001) associated with male infertility. The results suggest that the polymorphism might be a factor of male infertility in the Pakistani population.

Polymorphisms of glutathione S-transferase and methylenetetrahydrofolate reductase genes in Moldavian patients with ulcerative colitis: Genotype-phenotype correlation

Background

Glutathione S-transferases (GSTM1, GSTT1, and GSTP1) and methylenetetrahydrofolate reductase (MTHFR) are important enzymes for protection against oxidative stress. In addition, MTHFR has an essential role in DNA synthesis, repair, and methylation. Their polymorphisms have been implicated in the pathogenesis of ulcerative colitis (UC). The aim of the present study was to investigate the role of selected polymorphisms in these genes in the development of UC in the Moldavian population.

Methods

In a case-control study including 128 UC patients and 136 healthy individuals, GSTM1 and GSTT1 genotypes (polymorphic deletions) were determined using multiplex polymerase chain reaction (PCR). The GSTP1 rs1695 (Ile105Val), MTHFR rs1801133 (C677T), and MTHFR rs1801131 (A1298C) polymorphisms were studied with restriction fragment length polymorphism (RFLP) analysis. Genotype–phenotype correlations were examined using logistic regression analysis.

Results

None of the genotypes, either alone or in combination, showed a strong association with UC. The case-only sub-phenotypic association analysis showed an association of the MTHFR rs1801133 polymorphism with the extent of UC under co-dominant (p corrected = 0.040) and recessive (p corrected = 0.020; OR = 0.15; CI = 0.04–0.63) genetic models. Also, an association between the MTHFR rs1801131 polymorphism and the severity of UC was reported for the over-dominant model (p corrected = 0.023; coefficient = 0.32; 95% CI = 0.10–0.54).

Conclusion

The GST and MTHFR genotypes do not seem to be a relevant risk factor for UC in our sample. There was, however, evidence that variants in MTHFR may influence the clinical features in UC patients. Additional larger studies investigating the relationship between GST and MTHFR polymorphisms and UC are required.

Role of genetic mutations in folate-related enzyme genes on Male Infertility

Several studies showed that the genetic mutations in the folate-related enzyme genes might be associated with male infertility; however, the results were still inconsistent. We performed a meta-analysis with trial sequential analysis to investigate the associations between the MTHFR C677T, MTHFR A1298C, MTR A2756G, MTRR A66G mutations and the MTHFR haplotype with the risk of male infertility. Overall, a total of 37 studies were selected. Our meta-analysis showed that the MTHFR C677T mutation was a risk factor for male infertility in both azoospermia and oligoasthenoteratozoospermia patients, especially in Asian population. Men carrying the MTHFR TC haplotype were most liable to suffer infertility while those with CC haplotype had lowest risk. On the other hand, the MTHFR A1298C mutation was not related to male infertility. MTR A2756G and MTRR A66G were potential candidates in the pathogenesis of male infertility, but more case-control studies were required to avoid false-positive outcomes. All of these results were confirmed by the trial sequential analysis. Finally, our meta-analysis with trial sequential analysis proved that the genetic mutations in the folate-related enzyme genes played a significant role in male infertility.

MTHFR 677C>T polymorphism increases the male infertility risk: a meta-analysis involving 26 studies

Background and Objectives

Methylenetetrahydrofolate reductase (MTHFR) polymorphism may be a risk factor for male infertility. However, the epidemiologic studies showed inconsistent results regarding MTHFR polymorphism and the risk of male infertility. Therefore, we performed a meta-analysis of published case-control studies to re-examine the controversy.

Methods

Electronic searches of PubMed, EMBASE, Google Scholar and China National Knowledge Infrastructure (CNKI) were conducted to select eligible literatures for this meta-analysis (updated to June 19, 2014). According to our inclusion criteria and the Newcastle-Ottawa Scale (NOS), only high quality studies that observed the association between MTHFR polymorphism and male infertility risk were included. Crude odds ratio (OR) with 95% confidence interval (CI) was used to assess the strength of association between the MTHFR polymorphism and male infertility risk.

Results

Twenty-six studies involving 5,575 cases and 5,447 controls were recruited. Overall, MTHFR 677C>T polymorphism showed significant associations with male infertility risk in both fixed effects (CT+TT vs. CC: OR = 1.34, 95% CI: 1.23–1.46) and random effects models (CT+TT vs. CC: OR = 1.39, 95% CI: 1.19–1.62). Further, when stratified by ethnicity, sperm concentration and control sources, the similar results were observed in Asians, Caucasians, Azoo or OAT subgroup and both in population-based and hospital-based controls. Nevertheless, no significant association was only observed in oligo subgroup.

Conclusions

Our results indicated that the MTHFR polymorphism is associated with an increased risk of male infertility. Further well-designed analytical studies are necessary to confirm our conclusions and evaluate gene-environment interactions with male infertility risk.

Lack of association between genetic polymorphisms in three folate-related enzyme genes and male infertility in the Chinese population

PURPOSE

This study explored the possible association of four single nucleotide polymorphisms (SNPs) of the three folate-related enzyme genes: MTHFR C677T and A1298C, MTR A2756G and MTRR A66G, with male infertility in the Chinese population.

METHODS

The polymorphic distributions of the four SNPs (MTHFR C677T and A1298C, MTR A2756G and MTRR A66G) were investigated by the method of SNaPshot in a Chinese cohort including 296 idiopathic infertile males with azoospermia or oligozoospermia and 204 fertile males.

RESULTS

We found no evidence for an association between any of these variants (MTHFR C677T and A1298C, MTR A2756G and MTRR A66G) and male infertility.

CONCLUSIONS

There is no evidence for an association between male infertility and polymorphism of the three folate-related enzyme genes in the Chinese population.

MTHFR C677T and A1298C Genotypes and Haplotypes in Slovenian Couples with Unexplained Infertility Problems and in Embryonic Tissues from Spontaneous Abortions

The objective of this study was to analyze the methylenetetrahydrofolate reductases ( MTHFR s) C677T and A1298C genotype distributions in couples with unexplained fertility problems (UFP) and healthy controls, and to analyze the genotype and haplotype distribution in spontaneously aborted embryonic tissues (SAET) using allele specific polymerase chain reaction (PCR) in 200 probands with UFP, 353 samples of SAET and 222 healthy controls. The analysis revealed a significant overall representation of the 677T allele in male probands from couples with UFP ( p = 0.036). The combined genotype distribution for both MTHFR polymorphisms was also significantly altered (χ ² 21.73, p <0.001) although female probands made no contribution (χ ² 1.33, p = 0.72). The overall representation of the 677T allele was more pronounced in SAET (0.5 vs. 0.351 in controls, p <0.001) regardless of the karyotype status (aneuploidy vs. normal karyotype). In addition, the frequencies of the CA and CC haplotypes were significantly lower than in the control group ( p = 0.021 and p = 0.001, respectively), whereas the frequency of the TC haplotype was significantly higher than in controls ( p <0.0001). The presented findings indicate that only male probands contribute to the association of MTHFR mutations with fertility problems in grown adults and demonstrate a high prevalence of mutated MTHFR genotypes in SAET.

Significant impact of the MTHFR polymorphisms and haplotypes on male infertility risk

Background

Methylenetetrahydrofolate reductase (MTHFR) converts 5,10-methylene tetrahydrofolate to 5-methyl tetrahydrofolate and affects the activity of cellular cycles participating in nucleotide synthesis, DNA repair, genome stability, maintenance of methyl pool, and gene regulation. Genetically compromised MTHFR activity has been suggested to affect male fertility. The objective of the present study was to find the impact on infertility risk of c.203G>A, c.1298A>C, and c.1793G>A polymorphisms in the MTHFR gene.

Methods

PCR-RFLP and DNA sequencing were used to genotype the common SNPs in the MTHFR gene in 630 infertile and 250 fertile males. Chi-square test was applied for statistical comparison of genotype data. Linkage disequilibrium between the SNPs and the frequency of common haplotypes were assessed using Haploview software. Biochemical levels of total homocysteine (tHcy) and folic acid were measured. Meta-analysis on c.1298A>C polymorphism was performed using data from ten studies, comprising 2734 cases and 2737 controls.

Results

c.203G>A and c.1298A>C were found to be unrelated to infertility risk. c.1793G>A was protective against infertility (P = 0.0008). c.677C>T and c.1793G>A were in significant LD (D’ = 0.9). Folic acid and tHcy level did not correlate with male infertility. Pooled estimate on c.1298A>C data from all published studies including our data showed no association of this polymorphism with male infertility (Odds ratio = 1.035, P = 0.56), azoospermia (Odds ratio = 0.97, P = 0.74), or oligoasthenoteratozoospermia (Odds ratio = 0.92, p = 0.29). Eight haplotypes with more than 1% frequency were detected, of which CCGA was protective against infertility (p = 0.02), but the significance of the latter was not seen after applying Bonferroni correction.

Conclusion

Among MTHFR polymorphisms, c.203G>A and c.1298A>C do not affect infertility risk and c.1793G>A is protective against infertility. Haplotype analysis suggested that risk factors on the MTHFR locus do not extend too long on the DNA string.

Geographical distribution of MTHFR C677T, A1298C and MTRR A66G gene polymorphisms in China: findings from 15357 adults of Han nationality

Background

Methylenetetrahydrofolate reductase (MTHFR) C677T, A1298C and methionine synthase reductase (MTRR) A66G polymorphisms are important genetic determinants for homocysteine (Hcy) levels, and are associated with several disorders. These polymorphisms are heterogeneously distributed worldwide. Our objective was to explore the geographical distributions of these polymorphisms in China.

Methodologies

15357 healthy adults were recruited from 10 regions. Buccal samples were collected and genomic DNA was isolated. Genotyping was performed using the fluorogenic 5′-nuclease assay.

Principal Findings

The prevalence of the three polymorphisms among different populations from China varied significantly and showed apparent geographical gradients. For MTHFR C677T, the frequencies of the 677T allele and the 677TT genotype were significantly higher among northern populations and ranged from the lowest values (24.0% and 6.4%, respectively) in Hainan (southern) to the highest values (63.1% and 40.8%, respectively) in Shandong (northern). For MTHFR A1298C, the 1298C allele and the 1298CC genotype frequencies were significantly higher among southern populations and increased from low values (13.1% and 1.4%, respectively) in Shandong to high values (25.7% and 6.7%, respectively) in Hainan. For A66G, the 66G allele and the 66GG genotype frequencies increased from lower values (23.7% and 5.4%, respectively) in Shandong to higher values (29.2% and 8.6%, respectively) in Hainan. The overall frequency of the 677T allele, 677TT genotype, 1298C allele, 1298CC genotype, 66G allele and 66GG genotype in the Chinese Han population was 45.2%, 23.2%, 18.6%, 3.9%, 25.7%, and 6.6%, respectively. No gender differences were found in the prevalence of both the MTHFR C677T and MTRR A66G polymorphisms.

Conclusions

This study indicates that there are marked geographical variations in the prevalence of the three polymorphisms among Chinese Han populations. Our baseline data may be useful for future researches in related fields.