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

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.

Genetic variations as molecular diagnostic factors for idiopathic male infertility: current knowledge and future perspectives

INTRODUCTION

Infertility is a major health problem, worldwide, which affects 10-15% of couples. About half a percent of infertility cases are related to male-related factors. Male infertility is a complex disease that is the result of various insults as lifestyle issues, genetics, and epigenetic factors. Idiopathic infertility is responsible for 30% of total cases. The genetic factors responsible for male infertility include chromosomal abnormalities, deletions of chromosome Y, and mutations and genetic variations of key genes.

AREAS COVERED

In this review article, we aim to narrate performed studies on polymorphisms of essential genes involved in male infertility including folate metabolizing genes, oxidative stress-related genes, inflammation, and cellular pathways related to spermatogenesis. Moreover, possible pathophysiologic mechanisms responsible for genetic polymorphisms are discussed.

EXPERT OPINION

Analysis and assessment of these genetic variations could help in screening, diagnosis, and treatment of idiopathic male infertility.

The distribution in native populations from Mexico and Central America of the C677T variant in the MTHFR gene

OBJECTIVES

To explore evolutionary hypotheses for the high frequencies of a substitution in the methylenetetrahydrofolate reductase (MTHFR) gene, in Mexican and Central American Indigenous populations.

MATERIALS AND METHODS

We obtained allele frequencies for the C677T variant in the MTHFR gene and ecological information for 37 indigenous samples from Mexico and Central America. We calculated Hardy-Weinberg equilibrium and computed Fst statistics. We computed correlations between the samples' allele frequencies and ecological and geochemical variables.

RESULTS

Many of the samples have extremely high frequencies of the T allele ( q ¯  = 0.62, median = 0.66). In this region, the frequency of the T allele decreases from Southeast to Northwest and is significantly correlated with longitude, latitude, altitude, and insolation.

CONCLUSIONS

The native people of Central America and Mexico evolved high frequencies of an allele which has been shown to produce deleterious clinical effects including neural tube effects, cardiovascular events, and cancer. This allele has a clinal distribution in the region, perhaps associated with solar irradiation. As (Contreras-Cubas et al., 2016) noted, the traditional diet of these populations, which is high in folate, has likely mitigated the negative effect of the allele. It is of primary importance that their rights to their homeland and traditional diets be respected. It is a matter of Public Health to investigate whether this allele is a factor in the current wave of cardiovascular diseases affecting the majority population of this region, since it descends from the Native peoples and the Mediterranean population, which also has high frequencies of the allele.

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.

Correlation between methylenetetrahydrofolate reductase gene polymorphism and oligoasthenospermia and the effects of folic acid supplementation on semen quality

Background

The present study investigated the correlation between 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and oligoasthenospermia, as well as the effects of folic acid supplementation on semen quality.

Methods

The present study was a case control study. The PCR-chip assay was applied to analyze the distribution characteristics of the frequencies and genotypes of the MTHFR C677T allele in 167 Han Chinese patients with idiopathic male infertility (including 86 patients with oligospermia and 81 patients with asthenospermia) and in 78 males with normal semen parameters. Moreover, homocysteine (Hcy) levels were assessed for the different groups. Semen quality was measured following three months of folic acid supplementation for the oligospermia and asthenospermia groups.

Results

The cytosine-thymine (CT) genotype (50% vs. 39.5%) and the thymine-thymine (TT) genotype (51.2% vs. 7.7%) carriers in the oligospermia group exhibited significantly higher percentages compared with those of the control group. The percentage of the CT genotype carriers in the asthenospermia group was significantly higher compared with that of the control group (59.3% vs. 50%), while the frequency of the TT genotype was significantly increased (22.2% vs. 7.7%). Furthermore, serum Hcy levels in the oligospermia and asthenospermia groups were significantly higher compared with those of the control group. The data also demonstrated that sperm density increased significantly following three months of folic acid supplementation to patients with oligospermia or asthenospermia. In these patients, the highest increase was noted for the subjects carrying the TT genotype.

Conclusions

The MTHFR C677T mutation and the elevated Hcy levels are important risk factors for the development of oligoasthenospermia. Folic acid supplementation can significantly improve sperm density.

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.

Oxidative Stress and Polymorphism in MTHFR SNPs (677 and 1298) in Paternal Sperm DNA is Associated with an Increased Risk of Retinoblastoma in Their Children: A Case-Control Study

Sperm DNA is considered as the most vulnerable to oxidative stress-induced damage that also impairs global sperm DNA methylation leading to sperm-associated pathologies. C677T and A1298C polymorphisms of the methylene tetrahydrofolate reductase (MTHFR) gene affect MTHFR enzyme activity. This study was planned as a case-control study to determine the MTHFR gene polymorphisms in the fathers of children affected with sporadic nonfamilial heritable retinoblastoma in an Indian population. MTHFR polymorphisms for single nucleotide polymorphisms 677 and 1298 were also determined in sporadic nonfamilial heritable retinoblastoma patients to estimate the risk for retinoblastoma development and to evaluate the role of MTHFR in retinoblastoma pathogenesis.

The susceptibility of FSHB -211G > T and FSHR G-29A, 919A > G, 2039A > G polymorphisms to men infertility: an association study and meta-analysis

BACKGROUND

Male infertility is a complex disorder caused by genetic, developmental, endocrine, or environmental factors as well as unknown etiology. Polymorphisms in the follicle stimulating hormone beta subunit (FSHB) (rs10835638, c.-211G > T) and follicle stimulating hormone receptor (FSHR) (rs1394205, c.-29G > A; rs6165, c.919A > G; rs6166, c.2039 A > G) genes might disturb normal spermatogenesis and affect male reproductive ability.

METHODS

To further ascertain the aforementioned effects, we conducted a case-control study of 255 infertile men and 340 fertile controls from South China using the Mass ARRAY method, which was analyzed by the t-tests and logistic regression analysis using SPSS for Windows 14.0. In addition, a meta-analysis was performed by combining our results with previous reports using STATA 12.0.

RESULTS

In the FSHB or FSHR gene single nucleotide polymorphism (SNP) evaluation, no statistically-significant difference was found in the frequency of allelic variants or in genotype distribution between cases and controls. However, a significant association for the comparison of GAA (P: 0.022, OR: 0.63, 95%CI: 0.43-0.94) was seen between the oligozoospermia and controls in haplotype analysis of rs1394205/rs6165/rs6166. In the meta-analysis, rs6165G allele and rs6166 GG genotype were associated with increased risk of the male infertility.

CONCLUSIONS

This study suggested that FSHR GAA haplotype would exert protective effects against male sterility, which indicated that the combination of three SNP genotypes of FSHR was predicted to have a much stronger impact than either one alone. Then in the meta-analysis, a significant association was seen between FSHR rs6165, rs6166 polymorphisms and male infertility. In terms of male infertility with multifactorial etiology, further studies with larger sample sizes and different ethnic backgrounds or other risk factors are warranted to clarify the potential role of FSHB and FSHR polymorphisms in the pathogenesis of male infertility.

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.

Susceptibility to male infertility: replication study in Japanese men looking for an association with four GWAS-derived loci identified in European men

PURPOSE

A previous genome-wide association study in European men identified four single nucleotide polymorphism (SNP) loci associated with male infertility. Our aim was to replicate, if possible, the association of these SNPs with Japanese male infertility.

METHODS

We genotyped four SNPs (rs5911500, rs10246939, rs2059807, and rs11204546) in 517 Japanese patients with male infertility and 369 fertile controls using SNP-specific real-time polymerase chain reaction TaqMan assays. Subsequently, we divided patients with male infertility into azoospermia (n = 417) and oligospermia subgroups (n = 70).

RESULTS

The four SNPs previously identified in European men showed no significant association with collective male infertility in our Japanese cohort. However, allele frequency analysis did indicate a significantly higher frequency of the rs11204546 C allele of the OR2W3 gene in the oligospermia subset of infertility patients compared with controls (p = 0.0037; odds ratio = 1.74; 95 % confidence interval, 1.21-2.53).

CONCLUSIONS

Although this study was somewhat limited by overall sample size, the OR2W3 gene polymorphism rs11204546 was significantly associated with oligospermia in Japanese men, suggesting that OR2W3 might be involved in genetic susceptibility to Japanese male infertility as well as in European males.

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.

New genetic markers for male infertility

PURPOSE OF REVIEW

The purpose of this review is to highlight the most important advances in the field of genetics of male infertility, with particular attention to primary articles dealing with the identification of new genetic and epigenetic markers that could be translated into clinical practice in the near future.

RECENT FINDINGS

Copy number variations (CNVs) of the Y chromosome (gr/gr) deletions could already be included in the diagnostic workup of infertile men, although confirming studies are needed for CNVs on the X chromosome, as well for polymorphisms in some autosomal genes and telomere length in sperm. Methods need to be further standardized before sperm DNA analysis could be included in clinical practice, although they can help in defining some forms of idiopathic infertility. Epigenetic biomarkers are potentially important in elucidating the cause of idiopathic male infertility. Polymorphisms in FSHB/FSHR could be used in clinical practice to diagnose some forms of male infertility and as a pharmacogenetic marker for FSH treatment.

SUMMARY

New genetic causes and genetic risk factors have been identified in recent years and new technologies for genomic and postgenomic analyses (arrays, next-generation sequencing, proteomics, metabolomics, global methylome analysis and so on) are promising research fields. It is presumed that some of these genetic and epigenetic tests will be introduced in clinical practice in the near future.

Adaptive developmental plasticity in methylene tetrahydrofolate reductase (MTHFR) C677T polymorphism limits its frequency in South Indians

Methylene tetrahydrofolate reductase (MTHFR) C677T polymorphism shows considerable heterogeneity in its distribution in humans worldwide. The current study was conducted to investigate whether this polymorphism exhibited adaptive developmental plasticity in the control of the TT-genotype frequency. We screened 1,818 South Indian subjects (895 males and 923 females) for MTHFR C677T polymorphism using PCR-restriction fragment length polymorphism approach. MTHFR 677T-allele frequency in males and females was 9.1 and 11.0%, respectively. Compared to females, males had lower frequency of TT-genotype [odds ratio 0.31, 95% confidence interval (CI) 0.08-1.01]. The frequency of MTHFR 677T-allele was highest in the age group of 20-40 years and it gradually decreased from 40-60 to 60-80 years (P trend<0.0001). MTHFR 677TT-genotype was associated with 7.02-folds (95% CI: 2.12-25.63, P<0.0001) cumulative risk for recurrent pregnancy loss (RPL), neural tube defects (NTDs) and deep vein thrombosis (DVT). Linear regression model suggested that male gender exhibited increased homocysteine levels by 9.35 μmol/L while each MTHFR 677T-allele contributed to 4.63 μmol/L increase in homocysteine. Plasma homocysteine showed inverse correlation with dietary folate (r=-0.17, P<0.0001), B2 (r=-0.14, P<0.0001) and B6 (r=-0.07, P=0.03). Examination of the spontaneously aborted fetuses (n=35) showed no significant association of fetal genotype on its in utero viability. From the current study, it was concluded that C677T seemed to have acquired adaptive developmental plasticity among South Indians due to environmental influences thus contributing to hyperhomocysteinemia and its associated complications such as RPL, NTDs, DVT, etc.