Lack of association between the MTHFR (C677T) polymorphism and atopic disease

Methylene-tetrahydrofolate reductase contributes to allergic airway disease

Rationale

Environmental exposures strongly influence the development and progression of asthma. We have previously demonstrated that mice exposed to a diet enriched with methyl donors during vulnerable periods of fetal development can enhance the heritable risk of allergic airway disease through epigenetic changes. There is conflicting evidence on the role of folate (one of the primary methyl donors) in modifying allergic airway disease.

Objectives

We hypothesized that blocking folate metabolism through the loss of methylene-tetrahydrofolate reductase (Mthfr) activity would reduce the allergic airway disease phenotype through epigenetic mechanisms.

Methods

Allergic airway disease was induced in C57BL/6 and C57BL/6^Mthfr-/- mice through house dust mite (HDM) exposure. Airway inflammation and airway hyperresponsiveness (AHR) were measured between the two groups. Gene expression and methylation profiles were generated for whole lung tissue. Disease and molecular outcomes were evaluated in C57BL/6 and C57BL/6^Mthfr-/- mice supplemented with betaine.

Measurements and main results

Loss of Mthfr alters single carbon metabolite levels in the lung and serum including elevated homocysteine and cystathionine and reduced methionine. HDM-treated C57BL/6^Mthfr-/- mice demonstrated significantly less airway hyperreactivity (AHR) compared to HDM-treated C57BL/6 mice. Furthermore, HDM-treated C57BL/6^Mthfr-/- mice compared to HDM-treated C57BL/6 mice have reduced whole lung lavage (WLL) cellularity, eosinophilia, and Il-4/Il-5 cytokine concentrations. Betaine supplementation reversed parts of the HDM-induced allergic airway disease that are modified by Mthfr loss. 737 genes are differentially expressed and 146 regions are differentially methylated in lung tissue from HDM-treated C57BL/6^Mthfr-/- mice and HDM-treated C57BL/6 mice. Additionally, analysis of methylation/expression relationships identified 503 significant correlations.

Conclusion

Collectively, these findings indicate that the loss of folate as a methyl donor is a modifier of allergic airway disease, and that epigenetic and expression changes correlate with this modification. Further investigation into the mechanisms that drive this observation is warranted.

Folate status, regulatory T cells and MTHFR C677T polymorphism study in allergic children

PURPOSE

This study aimed to investigate early-life folate serum concentrations in children with food, inhalant or mixed type allergy. The influence of folate levels on the FoxP₃ expression in Treg (regulatory T) cells in the studied children, taking into account the MTHFR (5,10-methylenetetrahydrofolate reductase) genotypes was also analyzed.

MATERIAL AND METHODS

The study was performed in 83 allergic children (study group) and 49 healthy children (control group), aged 2-72 months. Medical history of each child was obtained and laboratory tests (serum folic acid concentrations and MTHFR C677T polymorphism) were carried out. The percentage of Treg cells was evaluated in almost a half of the examined subjects (48.5%).

RESULTS

Significantly higher serum folate levels in the group of children with food allergy than in those with inhalant allergy was confirmed (P=0.037). In the study group the TT homozygotes were characterized by significantly lower folate concentrations than CC homozygotes (P=0.045). A negative correlation was demonstrated between the FoxP₃ expression in CD4⁺CD25^highFoxP₃⁺ peripheral blood lymphocytes and serum folic acid concentrations. The correlation was more pronounced in the group of allergic children and it was statistically significant (r=-0.339, P<0.05).

CONCLUSIONS

The results of the study indicate a possibility of some effects of folate status on Treg cells, thus suggesting their potential role in the development and course of allergy in children.

Methylenetetrahydrofolate Reductase gene polymorphism in children with allergic rhinitis

BACKGROUND

Methylenetetrahydrofolate Reductase (MTHFR) polymorphisms by impairing folate metabolism may influence the development of allergic diseases. The results of studies evaluating the relationship between MTHFR polymorphisms and atopic disease are controversial. The aim of this study was to investigate the association between the polymorphisms of C677T and A1298C for MTHFR gene and allergic rhinitis (AR) in children.

METHODS

Ninety patients followed up with diagnosis of allergic rhinitis in our clinic and 30 children with no allergic diseases were included in the study. All participants were genotyped for the MTHFR (C677T) and (A1298C) polymorphisms. Vitamin b12, folate and homocysteine levels were measured.

RESULTS

The mean age of patients was 9.2±2.9 years; 66.7% of the patients were male. There was no significant difference between patient and control groups regarding gender, age and atopy history of the family (p>0.05). The frequency of homozygotes for MTHFR C677T polymorphism in the patient and control groups was 3.3% and 10%, respectively. The frequency of homozygotes for MTHFR A1298C polymorphism among groups was 26.7% and 16.7%, respectively. The association between allergic rhinitis and polymorphisms of C677T and A1298C for MTHFR gene was not statistically significant in patients compared with controls (p>0.05). There were no statistically significant differences between the patients and the control group in terms of serum vitamin b12, folate and homocysteine levels (p>0.05).

CONCLUSION

We found no evidence for an association between allergic rhinitis and polymorphisms of C677T and A1298C for MTHFR gene in children. Further studies investigating the relationship between MTHFR polymorphism and AR are required.

Is Folate Status a Risk Factor for Asthma or Other Allergic Diseases?

PURPOSE

It is controversial whether folate status is a risk factor for the development of asthma or other allergic diseases. This study was conducted to investigate whether indirect or direct exposure to folate and impaired folate metabolism, reflected as methylene-tetrahydrofolate reductase (MTHFR) C677T polymorphism, would contribute to the development of asthma and other allergic diseases.

METHODS

Electronic databases were searched to identify all studies assessing the association between folate status and asthma or other allergic diseases. Two reviewers independently assessed the eligibility of studies and extracted data. The relative risk (RR) or odds ratio (OR) with 95% confidence intervals (CI) was calculated and pooled.

RESULTS

Twenty-six studies (16 cohort, 7 case-control, and 3 cross-sectional studies) were identified. Maternal folic acid supplementation was not associated with the development of asthma, atopic dermatitis (AD), eczema, and sensitization in the offspring, whereas exposure during early pregnancy was related to wheeze occurrence in the offspring (RR=1.06, 95% CI=[1.02-1.09]). The TT genotype of MTHFR C677T polymorphism was at high risk of asthma (OR=1.41, 95% CI=[1.07-1.86]).

CONCLUSIONS

It is indicated that maternal folic acid supplementation during early pregnancy may increase the risk of wheeze in early childhood and that the TT genotype of MTHFR C677T polymorphism impairing folic acid metabolism would be at high risk of asthma development. These results might provide additional information for recommendations regarding forced folate consumption or folic acid supplements during pregnancy based on its well-established benefits for the prevention of congenital malformations. However, currently available evidence is of low quality which is needed to further elucidate.

Mendelian randomization studies: a review of the approaches used and the quality of reporting

BACKGROUND

Mendelian randomization (MR) studies investigate the effect of genetic variation in levels of an exposure on an outcome, thereby using genetic variation as an instrumental variable (IV). We provide a meta-epidemiological overview of the methodological approaches used in MR studies, and evaluate the discussion of MR assumptions and reporting of statistical methods.

METHODS

We searched PubMed, Medline, Embase and Web of Science for MR studies up to December 2013. We assessed (i) the MR approach used; (ii) whether the plausibility of MR assumptions was discussed; and (iii) whether the statistical methods used were reported adequately.

RESULTS

Of 99 studies using data from one study population, 32 used genetic information as a proxy for the exposure without further estimation, 44 performed a formal IV analysis, 7 compared the observed with the expected genotype-outcome association, and 1 used both the latter two approaches. The 80 studies using data from multiple study populations used many different approaches to combine the data; 52 of these studies used some form of IV analysis; 44% of studies discussed the plausibility of all three MR assumptions in their study. Statistical methods used for IV analysis were insufficiently described in 14% of studies.

CONCLUSIONS

Most MR studies either use the genotype as a proxy for exposure without further estimation or perform an IV analysis. The discussion of underlying assumptions and reporting of statistical methods for IV analysis are frequently insufficient. Studies using data from multiple study populations are further complicated by the combination of data or estimates. We provide a checklist for the reporting of MR studies.

Ethnic-specific associations of rare and low-frequency DNA sequence variants with asthma

Common variants at many loci have been robustly associated with asthma but explain little of the overall genetic risk. Here we investigate the role of rare (<1%) and low-frequency (1-5%) variants using the Illumina HumanExome BeadChip array in 4,794 asthma cases, 4,707 non-asthmatic controls and 590 case-parent trios representing European Americans, African Americans/African Caribbeans and Latinos. Our study reveals one low-frequency missense mutation in the GRASP gene that is associated with asthma in the Latino sample (P=4.31 × 10(-6); OR=1.25; MAF=1.21%) and two genes harbouring functional variants that are associated with asthma in a gene-based analysis: GSDMB at the 17q12-21 asthma locus in the Latino and combined samples (P=7.81 × 10(-8) and 4.09 × 10(-8), respectively) and MTHFR in the African ancestry sample (P=1.72 × 10(-6)). Our results suggest that associations with rare and low-frequency variants are ethnic specific and not likely to explain a significant proportion of the 'missing heritability' of asthma.

Asthma, allergy, and responses to methyl donor supplements and nutrients

After a brief period of stabilization, recent data have shown that the prevalence of asthma and allergic diseases continues to increase. Atopic diseases are major public health problems resulting in significant disability and resource use globally. Although environmental factors influence the development of atopic disease, dietary changes might partially explain the high burden of atopic disease. Potential mechanisms through which diet is suspected to effect asthma and allergy susceptibility are through epigenetic changes, including DNA methylation. Dietary methyl donors are important in the one-carbon metabolic pathway that is essential for DNA methylation. Findings from both observational studies and interventional trials of dietary methyl donor supplementation on the development and treatment of asthma and allergy have produced mixed results. Although issues related to the differences in study design partially explain the heterogeneous results, 2 other issues have been largely overlooked in these studies. First, these nutrients affect one of many pathways and occur in many of the same foods. Second, it is now becoming clear that the human intestinal microbiome is involved in the metabolism and production of the B vitamins and other methyl donor nutrients. Future studies will need to account for both the interrelationships between these nutrients and the effects of the microbiome.

MTHFR C677T genotype and cardiovascular risk in a general population without mandatory folic acid fortification

PURPOSE

Meta-analyses have suggested an effect of MTHFR C677T genotype (rs1801133), a proxy for blood total homocysteine, on cardiovascular disease (CVD) in populations with low population dietary folate. The aim was to examine the association and effect modification by serum folate and vitamin B12 levels between MTHFR and CVD-related outcomes in a general population with no mandatory folic acid fortification policy.

METHODS

The study population included 13,748 adults retrieved from pooling of four population-based studies conducted in Denmark. MTHFR genotype, serum folate (measured in approximately 9,356 individuals), and serum vitamin B12 (9,215 individuals), hypertension, and dyslipidemia were measured at baseline, and participants were followed for a mean of 10.5-11.7 years in central registries for diagnoses of stroke (623 incidents), ischaemic heart disease (IHD) (835 incidents), and all-cause mortality (1,272 incidents).

RESULTS

The MTHFR genotype (TT vs. CC/CT) was not associated with hypertension [OR (95% CI) 1.09 (0.95-1.25)], dyslipidemia [OR (95% CI) 0.97 (0.84-1.11)], stroke [HR (95% CI) 0.92 (0.69-1.23)], and all-cause mortality [HR (95% CI) 0.94 (0.77-1.14)], either overall, or in participants with low serum folate or B12 status (P values for interactions 0.15-0.94). Individuals with the MTHFR TT genotype had a higher risk of IHD (HR (95% CI) 1.38 (1.11-1.71)), but this association was not modified by folate status (P value for interaction 0.45).

CONCLUSIONS

Our results do not support a causal relationship between homocysteine and CVD. However, we cannot exclude a direct causal effect of MTHFR C677T genotype on IHD.

Folic acid use in pregnancy and the development of atopy, asthma, and lung function in childhood

BACKGROUND

Recently, folic acid supplementation during pregnancy was implicated as a potential risk factor for atopic diseases in childhood.

OBJECTIVE

To investigate whether folic acid supplementation and higher intracellular folic acid (ICF) levels during pregnancy increase the risk of childhood atopic diseases.

METHODS

In the KOALA Birth Cohort Study (N=2834), data on eczema and wheeze were collected by using repeated questionnaires at 3, 7, 12, and 24 months, 4 to 5 years, and 6 to 7 years after delivery. Atopic dermatitis and total and specific immunoglobulin E levels were determined at age 2 years and asthma and lung function at age 6 to 7 years. We defined folic acid use as stand-alone and/or multivitamin supplements according to the period of use before and/or during pregnancy. ICF levels were determined in blood samples taken at ∼35 weeks of pregnancy (n=837). Multivariable logistic and linear regression analyses were conducted, with generalized estimating equation models for repeated outcomes.

RESULTS

Maternal folic acid supplement use during pregnancy was not associated with increased risk of wheeze, lung function, asthma, or related atopic outcomes in the offspring. Maternal ICF level in late pregnancy was inversely associated with asthma risk at age 6 to 7 years in a dose-dependent manner (P for trend=.05).

CONCLUSIONS

Our results do not confirm any meaningful association between folic acid supplement use during pregnancy and atopic diseases in the offspring. Higher ICF levels in pregnancy tended, at most, toward a small decreased risk for developing asthma.

Study of folate status among Egyptian asthmatics

OBJECTIVE

To compare serum folate levels between atopic asthmatics, non-atopic asthmatics, and healthy controls.

METHODS

This case-control study included 60 asthmatics with at least one positive skin prick test (SPT) reaction (atopic asthma group), 60 asthmatics with negative SPT reactions (non-atopic asthma group), and 60 healthy controls with no history of asthma or other allergic diseases, and with negative SPT reactions. Serum folate and total IgE levels were measured in all subjects. In addition, lung functions were assessed by spirometry.

RESULTS

Serum folate levels were significantly lower among the atopic asthma group [9.1 (4.9, 12.1) ng/mL] as compared to the non-atopic asthma group [11.3 (7.5, 14.8) ng/mL] and the control group [12.0 (8.3, 15.1) ng/mL], p= 0.001. Among atopic asthmatics, serum folate levels were inversely correlated with total serum IgE levels (r=-0.483, p<0.001), and the number of positive SPT reactions (r=-0.442, p<0.001). Atopic asthmatics with a total serum IgE ≤200 IU/mL had significantly higher levels of serum folate than those with a total serum IgE >200 IU/mL. Regression analysis showed that higher folate levels independently predicted lower total serum IgE levels. Folate was not found to be an independent predictor of asthma. No association was observed between serum folate levels and values of forced expiratory volume in 1s.

CONCLUSION

Among asthmatics, serum folate levels are significantly lower among atopics, and correlate inversely with the degree of atopy.

Atopy, asthma, and lung function in relation to folate and vitamin B(12) in adults

BACKGROUND

Recent studies suggested low serum folate and impaired folate metabolism as potential risk factors for development of asthma and atopic disease, but the results are inconsistent. The aim of this study was to investigate the relations of markers of folate and vitamin B₁₂ (B₁₂) deficiency with different phenotypes of asthma and atopy.

METHODS

A random sample of 6784 persons from a general population aged 30-60 years participated in a health examination in 1999-2001, and 4516 (66.6%) of those also participated in a follow-up examination 5 years later. The examinations included spirometry, measurements of serum folate and B₁₂, specific IgE to inhalant allergens, total IgE, and genotyping of the MTHFR-C677T polymorphism - a genetic marker of impaired folate metabolism. Information about dietary intake of folate and B₁₂, asthma diagnosis, and airway symptoms was obtained by questionnaires.

RESULTS

Low serum folate levels and the TT genotype of the MTHFR-C677T polymorphism were associated with increased prevalence of self-reported doctor-diagnosed asthma [odds ratio (OR) 1.37, 95% confidence interval (CI) 1.05-1.79 and OR 1.52; 95% CI 1.12-2.06, respectively] and attacks of shortness of breath (OR 1.43, 95% CI 1.14-1.79 and OR 1.47; 95% CI: 1.14-1.91, respectively). We found no significant associations with lung function or atopic outcomes. Serum levels of B₁₂ and dietary intake of folate and B₁₂ were not associated with asthma or atopy.

CONCLUSIONS

We found that two objective markers of folate deficiency were associated with self-reported doctor-diagnosed asthma and attacks of shortness of breath, but not with lung function or atopy.