Distribution of 1298A > C polymorphism of methylenetetrahydrofolate reductase gene in patients with bipolar disorder and schizophrenia

Association between variants of MTHFR genes and psychiatric disorders: A meta-analysis

Background

Psychiatric disorders have seriously affected human life, one of the risk genes related to psychosis is the methylenetetrahydrofolatereductase (MTHFR) gene. This gene has a potential role in psychiatric disorders. Therefore, a meta-analysis is conducted to investigate the correlations between two prevalent MTHFR single nucleotide polymorphisms (SNPs), MTHFR C677T, A1298C, severe psychological disorders (schizophrenia, major depression, bipolar disorder).

Methods

A total of 81 published studies were screened and selected by a search of electronic databases up to April 2022. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the association between MTHFR polymorphism and psychiatric disorders susceptibility by using random effect models.

Results

We found that MTHFR C677T polymorphism is significantly related to schizophrenia and major depression in the overall population. MTHFR C677T has been linked to an increased risk of bipolar disorder in the recessive model (TT vs. CT + CC). Ethnic subgroup analysis shows that schizophrenia and major depression significantly correlate with MTHFR C677T and A1298C in Asian populations but not Caucasians. Besides, schizophrenia is correlated substantially with MTHFR C677T in the African population. However, the MTHFR A1298C polymorphism is only marginally linked to major depression.

Conclusion

Findings of the current study revealed that MTHFR may contribute to the common pathogenesis of psychiatric diseases and that its variants may be essential in controlling the expression of psychosis-related genes. This study could help the researchers and health specialists in the early diagnosis and treatment of psychiatric disorders.

Association between MTHFR (677C>T and 1298A>C) polymorphisms and psychiatric disorder: A meta-analysis

Recent studies showed that genetic polymorphism of 5,10-methylenetetrahydrofolate reductase (MTHFR) is related to attention-deficit hyperactivity disorder (ADHD), bipolar disorder (BD) and schizophrenia (SCZ). However, no consistent conclusion has been determined. This meta-analysis aims to interrogate the relationship between MTHFR gene polymorphisms (677C>T and 1298A>C) and the occurrence of ADHD, BD and SCZ. We retrieved case-control studies that met the inclusion criteria from the PubMed database. Associations between MTHFR polymorphisms (677C>T and 1298A>C) and ADHD, BD and SCZ were measured by means of odds ratios (ORs) using a random effects model and 95% confidence intervals (CIs). Additionally, sensitivity analysis and publication bias were performed. After inclusion criteria were met, a total of five studies with ADHD including 434 cases and 670 controls, 18 studies with BD including 4167 cases and 5901 controls and 44 studies with SCZ including 16,098 cases and 19913 controls were finally included in our meta-analysis. Overall, our meta-analytical results provided evidence that the MTHFR 677C>T was associated with occurrence of BD and SCZ, while the 1298A>C polymorphism was related to ADHD and BD, and additionally the sensitivity analysis indicated these results were stable and reliable. This may provide useful information for relevant studies on the etiology of psychiatric disorders.

MAD1L1 and TSNARE gene polymorphisms are associated with schizophrenia susceptibility in the Han Chinese population

BACKGROUND

Schizophrenia (SCZ) is a severe mental illness with high heritability. This study aimed to explore the correlation between MAD1L1, TSNARE polymorphisms and SCZ susceptibility.

METHODS

A total of 493 SCZ patients and 493 healthy controls were included. The genotypes of MAD1L1 and TSNARE polymorphisms were identified by Agena MassARRAY platform. Odds ratio (OR) and 95% confidence intervals (CIs) were tested via logistic regression analysis in multiple genetic models and different subgroups.

RESULTS

We observed that AG genotype of rs1107592, AG genotype of rs4976976, and CA genotype of rs67756423 decreased the susceptibility to SCZ (p < 0.05). Age stratification analysis showed that the TC genotype of rs12666575, AG genotype of rs1107592, and AG genotype of rs4976976 decreased the risk of SCZ individuals older than 36 years (p < 0.05). In addition, the AG and AA genotype of rs4976976, the CA genotype of rs67756423 were associated with a lower risk of SCZ in males (p < 0.05). In females, the TT genotype of rs12666575 in recessive model, the AG and AA-AG genotype of rs1107592 in heterozygote and dominant model, could reduce the susceptibility to SCZ (p < 0.05). However, no significant association was found after Bonferroni correction.

CONCLUSIONS

Our results suggest that MAD1L1 and TSNARE genetic polymorphisms exert a protective role in the risk of SCZ. These findings provide evidence that MAD1L1 and TSNARE may serve as potential biomarkers of SCZ. However, a replication experiment in a cohort with large sample size are required to confirm our findings. Trial registration Not applicable.

Homocysteine as a peripheral biomarker in bipolar disorder: A meta-analysis

Background:

Bipolar disorder (BD) is a psychiatric disorder with an uncertain aetiology. Recently, special attention has been given to homocysteine (Hcy), as it has been suggested that alterations in 1-carbon metabolism might be implicated in diverse psychiatric disorders. However, there is uncertainty regarding possible alterations in peripheral Hcy levels in BD.

Methods:

This study comprises a meta-analysis comparing serum and plasma Hcy levels in persons with BD and healthy controls. We conducted a systematic search for all eligible English and non-English peer-reviewed articles.

Results:

Nine cross-sectional studies were included in the meta-analyses, providing data on 1547 participants. Random-effects meta-analysis showed that serum and plasma levels of Hcy were increased in subjects with BD in either mania or euthymia when compared to healthy controls, with a large effect size in the mania group (g= 0.98, 95% CI: 0.8–1.17,P< 0.001,n= 495) and a small effect in the euthymia group (g= 0.3, 95% CI: 0.11–0.48,P= 0.002,n= 1052).

Conclusions:

Our meta-analysis provides evidence that Hcy levels are elevated in persons with BD during mania and euthymia. Peripheral Hcy could be considered as a potential biomarker in BD, both of trait (since it is increased in euthymia), and also of state (since its increase is more accentuated in mania). Longitudinal studies are needed to clarify the relationship between bipolar disorder and Hcy, as well as the usefulness of peripheral Hcy as both a trait and state biomarker in BD.

Genetic association of GWAS-supported MAD1L1 gene polymorphism rs12666575 with schizophrenia susceptibility in a Chinese population

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with high heritability. A recent European genome-wide association study has reported that mitotic arrest deficient-like 1 (MAD1L1) polymorphism rs12666575 is associated with SCZ susceptibility. This study aims to test the association of MAD1L1 variant rs12666575 with SCZ susceptibility in a Chinese population. A total of 1400 participants, which include 700 SCZ patients and 700 sex- and age-matched controls (Zhuang: 300, Han: 400, respectively), were genotyped using the Sequenom MassARRAY iPLEX platform. 591 SCZ patients underwent positive and negative syndrome scale (PANSS) assessment. Genetic association analysis was performed using the PLINK program. The results showed MAD1L1 rs12666575 polymorphism was significantly associated with SCZ susceptibility in the recessive model (p(adj)=0.013). Also, rs12666575 was significantly associated with general psychopathology sub-scale score (p(adj)=0.043) and thought disturbance factor score (p(adj)=0.045). Our data suggested that MAD1L1 rs12666575 polymorphism may play a protective role against SCZ in the Chinese population. Furthermore, rs12666575 may be associated with general psychopathology and thought disturbance in SCZ patients.

Homocysteine as a potential biomarker in bipolar disorders: a critical review and suggestions for improved studies

INTRODUCTION

Homocysteine levels have been associated with major depression, but associations with bipolar disorder remain less clear. Some data suggest homocysteine levels have potential as a biomarker of treatment response; however the literature is mixed.

AREAS COVERED

Oxidized forms of homocysteine can be potentially neurotoxic leading to glutamate toxicity, apoptotic transformation and neurodegenerative processes. High homocysteine may be a risk biomarker for bipolar disorders, but the empirical base remains too weak for firm conclusions. This review discusses the current literature for homocysteine levels as a biomarker.

EXPERT OPINION

It is premature to foreclose the utility of homocysteine levels as a biomarker for bipolar disorder due the methodological inadequacies in the existing literature. These methodological design issues include lack of control for the confounding variables of concurrent medication, phase of bipolar disorder, gender, age, nutritional status, thyroid, liver and renal function, smoking or lean body mass. Well-powered association studies with confounder control could help shed more light on the important clinical question of homocysteine's utility as a biomarker in bipolar disorder. Future experiments are needed to examine the outcome of interventions modulating homocysteine for treating bipolar disorder. Only prospective randomized control trials will provide definitive evidence of the utility of homocysteine as a biomarker or therapeutic target.

Are genes connected with homocysteine metabolism associated with bipolar disorder?

BACKGROUND

Increased levels of homocysteine have been observed in various psychiatric disorders, among them in schizophrenia, depression and bipolar mood disorder. Of the genes connected with homocysteine metabolism, some studies have found an association between polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene and bipolar disorder. The aim of this study was to investigate a possible association between 5 polymorphisms of 4 genes coding enzymes of homocysteine metabolism and bipolar disorder.

METHOD

A total of 120 patients with bipolar disorder (24 male, 96 female) and 167 subjects from the general population (81 male, 86 female) were included in the study. Genotyping was performed for the C677T (rs1801133) and A1298C (rs1801131) polymorphisms of the MTHFR gene, for the T833C polymorphism (rs5742905) of the cystathionine-β-synthase (CBS) gene, for the A2756G polymorphism (rs1805087) of the homocysteine methyltransferase gene, and for the A66G polymorphism (rs1801394) of the methionine synthase reductase (MTRR) gene.

RESULTS

An association with bipolar disorder was found for the T833C polymorphism (rs5742905) of the CBS gene. However, in the patient sample, the genotypes of this polymorphism were not in Hardy-Weinberg equilibrium. No relationship to bipolar disorder was obtained for the remaining polymorphisms studied.

CONCLUSIONS

These results are the first suggesting a possible association between T833C polymorphism (rs5742905) of the CBS gene and bipolar disorder. We were unable to confirm an association between bipolar disorder and C677T polymorphism (rs1801133) of the MTHFR gene, as suggested in some previous studies.

Methylenetetrahydrofolate reductase (MTHFR) polymorphism susceptibility to schizophrenia and bipolar disorder: an updated meta-analysis

Previous studies examining the possible role of the methylenetetrahydrofolate reductase (MTHFR) polymorphisms in the development of schizophrenia (SZ) and bipolar disorder (BPD) have provided inconclusive findings, this meta-analysis was therefore designed to get a more reliable assessment. A total of 38 articles were identified through a search of electronic databases, up to 27 February 2014. Odds ratios (ORs) with 95% confidence interval (CIs) were calculated using random effects models. Meta-analysis showed that MTHFR C677T was significantly associated with SZ, the highest OR was found for the recessive model (for TT vs. CT + CC: OR = 1.34, 95% CI: 1.18-1.53); a marginal association of MTHFR C677T with increased risk of BPD has also been found for the recessive model (OR = 1.26, 95% CI: 1.00-1.59). Subgroup analysis by ethnicity indicated that the significant association with SZ and BPD existed among Asian and African populations, but not for the white. MTHFR A1298C was significant associated with SZ, the highest OR for the dominant model (OR = 1.13, 95% CI: 1.03-1.24). Subgroup analysis indicated a significant association with SZ existed in Asian populations, not among the white populations and no significant association was detected between the MTHFR A1298C and BPD in all groups. We conclude that MTHFR polymorphism is associated with SZ and BPD among Asian, African populations, but not the white.

Homocysteine and MTHFR C677T polymorphism in children and adolescents with psychotic and mood disorders

BACKGROUND

High level of homocysteine (Hcy) is risk factor of schizophrenia and mood disorders.

AIM

The aim was to detect a serum level of Hcy, examine the associations between the level of Hcy, methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism and clinical properties for patients with schizophrenia, mood disorders and in a control group.

MATERIAL AND METHODS

There were 88 patients with schizophrenia, 28 with affective disorders and 94 from the control group. The Hamilton Anxiety Scale (HAM-A) was performed to study anxiety, the Hamilton Depression Scale (HAM-D) to study depression and the Brief Psychiatric Rating Scale (BPRS) to study severity of schizophrenia. The level of Hcy was stated by isocratic high-performance liquid chromatography (HPLC) system with fluorometric detection. DNA isolation from venous blood was performed by the phenol-chloroform method.

RESULTS

The levels of B12 vitamin and folic acid were within normal limits for all the patients. The average level of Hcy was 11.94 ± 5.6 μmol/l for patients with schizophrenia and 11.65 ± 3.3 μmol/l for patients with affective disorders, vs. 6.80 ± 2.93 μmol/l in a control group. The highest level of Hcy has been observed in patients with an episodic-recurrent course of schizophrenia, paranoid schizophrenia-continuous, particularly in patients with CT genotype (r = - 0.58; P < 0.01). In the given diagnostic groups, the highest level of anxiety was observed.

CONCLUSIONS

The level of Hcy is higher in the blood of a heterozygotic person who becomes ill with schizophrenia, and the process of the illness is more serious and with more typical affective disorders.

Implication de la mutation A1298C du gène MTHFR dans la survenue de la schizophrénie

Introduction

La schizophrénie (scz) est un problème majeur de santé publique, puisqu’il s’agit d’une pathologie redoutable du sujet jeune, qui atteint 1 % de la population générale. Le terme schizophrénie désigne une psychose marquée par l’altération de la vie psychique dans les secteurs de la pensée, de l’affectivité et du dynamisme vital. Il s’agit d’une maladie multifactorielle, et malgré l’absence de description claire d’un modèle de vulnérabilité, certains facteurs de risque génétiques tels que la mutation A1298C du gène MTHFR est à l’heure actuelle étudiée.

Patients et méthodes

Notre étude a porté sur 51 patients schizophrènes recrutés au service de psychiatrie et 100 témoins. La mutation A1298C du gène MTHFR a été étudiée par la technique de PCR-RFLP. La digestion enzymatique a été effectuée avec MboII.

Résultat et discussion

Notre étude suggère une association positive entre le génotype hétérozygote AC (Δ2 = 91,15, p < 10−3) et CC (Δ2 = 9,36, p = 0,002) et la scz. Les généotypes AC et CC semblent de ce fait prédisposer à la maladie. Le rôle de la mutation demeure jusqu’à maintenant ambigu, cependant, l’hypothèse la plus probable relie les génotypes AC et CC avec une diminution de la concentration en S-adénosylméthionine induisant des troubles neuropsychiatriques.

Conclusion

La mutation A1298C semble être impliquée dans l’apparition de la scz, cependant, l’augmentation du nombre des patients révèlera mieux le rôle du gène MTHFR dans la physiopathologie de la scz.

Association between MTHFR C677T and A1298C, and MTRR A66G polymorphisms and susceptibility to schizophrenia in a Syrian study cohort

The folate-homocystiene metabolic pathway has been shown to be involved in the susceptibility for developing schizophrenia by several studies. In the present study we investigated the role of three common polymorphisms of the folate-homocysteine metabolic pathway in an Arab population from Syria consisting of 85 schizophrenic patients and 126 healthy controls. The studied polymorphisms included the MTHFR C677T and A1298C, and MTRR A66G, all of which result into amino acid changes, and were previously shown to yield decreased enzymatic activity and alter plasma homocysteine concentration. While MTHFR C677T and A1298C polymorphisms were not previously studied in an Arab population with respect to the susceptibility for developing schizophrenia, the MTRR A66G was not previously investigated in any population around the world. Our results indicated a strong association between MTHFR A1298C and schizophrenia. The variant C allele frequency was significantly higher in the patients group (40% vs 29.4%, OR=1.6, 95% CI (1.06-2.41), p=0.023). A statistically significant association was found for MTHFR 677TT genotype under the recessive model in the male patients subgroup (OR=2.6, 95% CI (1.04-6.5), p=0.036), and MTHFR 677CT genotype under the overdominant model in the total patients group (OR=0.52 95% CI (0.29-0.92), p=0.024). No statistically significant association was found for MTRR A66G polymorphism on an individual basis. However, a borderline association was found for the CC/GG (C677T/A66G) compound genotype (OR=2.24, 95% CI (0.97-5.15), p=0.053). Our results support the hypothesis of association between schizophrenia and folate-homocystiene metabolic pathway genes.

Elevated serum levels of homocysteine as an early prognostic factor of psychiatric disorders in children and adolescents

Background and Goal. The aim was to examine the serum levels of homocysteine (Hcy) and their associations with the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism in patients with schizophrenia and mood disorders as well as controls. Materials and Methods. There were 198 patients: 82 with schizophrenia spectrum disorders, 22 with mood disorders, and 94 controls. The level of Hcy was determined by an isocratic high-performance liquid chromatography system. MTHFR C677T polymorphism was analysed using the restriction fragment length polymorphism-polymerase chain reaction method. Results. The average level of Hcy was 11.94 ± 5.6 μmol/L for patients with schizophrenia, 11.65 ± 3.3 μmol/L for patients with affective disorders, versus 6.80 ± 2.93 μmol/L in a control. The highest level of Hcy has been observed in patients with episodic-recurrent course of schizophrenia (11.30 ± 7.74 μmol/L), paranoid schizophrenia continuous (12.76 ± 5.25 μmol/L), and in patients with affective disorders (11.65 ± 3.26 μmol/L). An association between the MTHFR gene C677T polymorphism and Hcy level was found by linear regression analysis (r = 1.41, P = 0.029). Conclusions. The data indicate a link between Hcy levels and schizophrenia and mood disorders. No associations between the level of Hcy in patients with schizophrenia and mood disorders and the MTHFR C677T polymorphism were found.

Hyperhomocysteinemia in Tunisian bipolar I patients

AIMS

The aim of the present study was to investigate hyperhomocysteinemia in Tunisian bipolar I patients according to 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism.

METHODS

The subjects consisted of 92 patients with bipolar I disorder diagnosed according to DSM-IV, and 170 controls. Plasma total homocysteine, folate and vitamin B12 were measured. MTHFR C677T polymorphism was determined by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Compared with controls, patients had a significantly higher homocysteine level (16.4 ± 9.8 vs 9.6 ± 4.5 µmol/L; P < 0.001) and a significantly lower folate level (3.2 ± 0.9 vs 6.5 ± 3.2 µg/L; P < 0.001). C677T MTHFR polymorphism genotype frequencies were in Hardy-Weinberg equilibrium. After adjustment for MTHFR C677T genotypes, hypofolatemia, hypovitamin B12 and for potential confounding factors, the odds ratio (OR) of hyperhomocysteinemia associated with bipolar disorder remained significant (OR, 5.53; 95% confidence interval: 1.92-15.86; P = 0.001). In patients, there was no significant change in hyperhomocysteinemia, hypofolatemia and hypovitamin B12 with regard to the clinical and therapeutic characteristics, whereas the highest prevalence of hyperhomocysteinemia was found in depressive patients and when illness duration was >12 years. Hypofolatemia was seen in all patients on lithium and in the majority of patients on carbamazepine, and the highest prevalence of hypovitamin B12 was noted in patients taking carbamazepine.

CONCLUSION

Hyperhomocysteinemia was more frequent in bipolar I patients independent of C677T polymorphism. Patients had reduced levels of folate, which modulates homocysteine metabolism. Indeed, this finding indicates that folate supplementation may be appropriate for bipolar patients with hyperhomocysteinemia.

Meta-analysis of MTHFR gene variants in schizophrenia, bipolar disorder and unipolar depressive disorder: evidence for a common genetic vulnerability?

Past analyses examining the relationship between genetic variation in the 5, 10-methylenetetrahydrofolate reductase (MTHFR) gene and psychiatric disorders have provided mixed and largely inconclusive findings. MTHFR is involved in the one-carbon metabolic pathway which is essential for DNA biosynthesis and the epigenetic process of DNA methylation. We conducted a meta-analysis of all published case-control studies investigating associations between two common MTHFR single nucleotide polymorphisms (SNPs), MTHFR C677T (sample size 29,502) and A1298C (sample size 7934), and the major psychiatric disorders (i) schizophrenia (SZ), (ii) bipolar disorder (BPD), and (iii) unipolar depressive disorder (UDD). In order to examine possible shared genetic vulnerability, we also tested for associations between MTHFR and all of these major psychiatric disorders (SZ, BPD and UDD) combined. MTHFR C677T was significantly associated with all of the combined psychiatric disorders (SZ, BPD and UDD); random effects odds ratio (OR)=1.26 for TT versus CC genotype carriers; confidence interval (CI) 1.09-1.46); meta-regression did not suggest moderating effects of psychiatric diagnosis, sex, ethnic group or year of publication. Although MTHFR A1298C was not significantly associated with the combination of major psychiatric disorders, nor with SZ, there was evidence for diagnostic moderation indicating a significant association with BPD (random effects OR=2.03 for AA versus CC genotype carriers, CI: 1.07-3.86). Meta-analysis on UDD was not possible due to the small number of studies available. This study provides evidence for shared genetic vulnerability for SZ, BPD and UDD mediated by MTHFR 677TT genotype, which is in line with epigenetic involvement in the pathophysiology of these psychiatric disorders.

No association of functional polymorphisms in methlylenetetrahydrofolate reductase and the risk and minor physical anomalies of schizophrenia in Korean population

Methylenetetrahydrofolate reductase (MTHFR), a critical enzyme in folate metabolism, plays an important role in DNA methylation. It has been suggested that abnormal DNA methylation contributes to the pathogenesis of schizophrenia and congenital anomalies. The previous findings regarding the genetic relationship between MTHFR and schizophrenia are controversial. This study investigated the association of the two functional polymorphisms of MTHFR, C677T and A1298C, with the risk for schizophrenia. Furthermore, we conducted an updated meta-analysis on the two polymorphisms. In addition, we investigated the relationship between the polymorphisms and minor physical anomaly (MPA), which may represent neurodevelopmental aberrations in 201 schizophrenia patients and 350 normal control subjects. There was no significant association between either of the two polymorphisms and the risk of schizophrenia (chi-square = 0.001, df = 1, P = 0.971 for C677T; chi-square = 1.319, df = 1, P = 0.251 for A1298C). However, in meta-analysis, the C677T polymorphism showed a significant association in the combined and Asian populations (OR = 1.13, P = 0.005; OR = 1.21, P = 0.011, respectively) but not in the Korean and Caucasian populations alone. Neither polymorphism was associated with MPAs measured by the Waldrop scale (chi-square = 2.513, df = 2, P = 0.285). In conclusion, the present findings suggest that in the Korean population, the MTHFR polymorphisms are unlikely to be associated with the risk for schizophrenia and neurodevelopmental abnormalities related to schizophrenia.

Methylenetetrahydrofolate reductase gene polymorphisms in Turkish children with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common, multifactorial genetic disorder. The aim of the present study was to evaluate a possible association between 5,10-methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms and ADHD. There is evidence to suggest that MTHFR C677T and A1298C polymorphisms alter the function of the enzyme, causing reduced folate and increased homocysteine levels in plasma. Two polymorphisms of the MTHFR gene, C677T (rs1801133) and A1298C (rs1801131), were analyzed in a sample of 100 Diagnostic and Statistical Manual of Mental Disorders-IV-diagnosed ADHD and 300 healthy controls using a polymerase chain reaction-restriction fragment length polymorphism method. We did not find any association between MTHFR 677T allele, MTHFR 1298C allele, and ADHD. In addition, there was no genotype association between the MTHFR gene and ADHD (χ(2)=1.711; df=2; p=0.425; χ(2)=2.946; df=2; p=0.229). Our data suggest that neither the MTHFR C677T polymorphism nor the MTHFR A1298C polymorphism was associated with ADHD in Turkish children. Thus, the MTHFR gene does not seem to play a role in the etiopathogenesis of ADHD in the cohort studied.

Methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C polymorphisms and age of onset in schizophrenia: a combined analysis of independent samples

Methylenetetrahydrofolate reductase (MTHFR) is involved in the one-carbon cycle, which is of importance for nucleotide synthesis and methylation of DNA, membranes, proteins and lipids. The MTHFR gene includes two common polymorphisms (rs1801133 or C677T; rs1801131 or A1298C) which both alter enzyme activity. The T-allele of the C677T polymorphism has recently been associated with earlier age at onset of schizophrenia. In the present study we examined the association between the MTHFR C677T and A1298C polymorphisms and age at onset of schizophrenia in twelve samples consisting of 3,213 unrelated schizophrenia patients, including the original Scandinavian sample. There was no consistent relationship between MTHFR C677T, A1298C or combined 677T/1298C carriers and age of onset in schizophrenia when the results of each study were combined using meta-analysis. The present results suggest that the investigated MTHFR polymorphisms do not influence age of onset in schizophrenia.

Gene-wide association study between the methylenetetrahydrofolate reductase gene (MTHFR) and schizophrenia in the Japanese population, with an updated meta-analysis on currently available data

Methylenetetrahydrofolate reductase (MTHFR) is a critical molecule for single-carbon transfer reactions. Recent evidence suggests that polymorphisms of MTHFR are related to neural tube deficits and the pathogenesis of schizophrenia. While several studies have demonstrated associations between the gene encoding the MTHFR (MTHFR) polymorphisms and schizophrenia, these studies lack consistency. Therefore, we conducted a gene-wide association study (patients with schizophrenia = 696, control subjects = 747) and performed imputation analysis. Additionally, we performed meta-analysis on currently available data from 18 studies for two common functional polymorphisms (rs1801131 and rs1801133). There were no significant associations with schizophrenia in the single marker analysis for the seven tagging SNPs of MTHFR. In the haplotypic analysis, a nominally significant association was observed between the haplotypes, which included four SNPs (rs1801133, rs17421511, rs17037396, and rs9651118) and the schizophrenic patients. Additionally, the imputation analysis demonstrated there were several associated markers on the MTHFR chromosomal region. However, confirmatory analyses of three tagging SNPs (rs1801133, rs17037396, and rs9651118) and the top SNP (rs17421511) for the imputation results (patients with schizophrenia = 797, control subjects = 1025) failed to replicate the haplotypic analysis and the imputation results. These findings suggest that MTHFR polymorphisms are unlikely to be related to the development of schizophrenia in the Japanese population. However, since our meta-analysis results demonstrated strong support for association of rs1801133 with schizophrenia, further replication studies based on a gene-wide approach need to be considered.

Association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and age of onset in schizophrenia

Different lines of evidence indicate that methylenetetrahydrofolate reductase (MTHFR) functional gene polymorphisms, causative in aberrant folate-homocysteine metabolism, are associated with increased vulnerability to several heritable developmental disorders. Opposing views are expressed considering the possible association between MTHFR and susceptibility for schizophrenia. In order to evaluate if age of onset could explain some of this discrepancy we investigated the relationship between two functional MTHFR gene polymorphisms and age at onset in this disorder. Scandinavian patients (n = 820) diagnosed with schizophrenia, schizoaffective disorder, and schizophreniform disorder were investigated. Two functional MTHFR single nucleotide polymorphisms (SNPs; rs1801131 and rs1801133) were genotyped and the effect of MTHFR polymorphisms on the age of onset was examined with survival analysis. In an attempt to replicate the findings from the Scandinavian sample, the association between rs1801133 and age at onset was also analyzed in Chinese high-risk families, with two or more affected siblings (n = 243). Among the Scandinavian patients the functional MTHFR SNP rs1801133 (C677T) significantly affected age at onset of schizophrenia in a dose-dependent manner (P = 0.0015), with lower age of onset with increasing numbers of the mutant T-allele. There was no evidence of rs1801131 (A1298C) affecting age of onset in schizophrenia. Within the Chinese high-risk families carriers of the MTHFR 677T allele showed earlier age at onset than siblings being homozygous for the wild-type allele (P = 0.008). The MTHFR C677T polymorphism may play a role as a modifying factor for age of onset in schizophrenia.

Folic acid fortification: a double-edged sword

PURPOSE OF REVIEW

To examine the impact of folic acid fortification, including its use as a functional food component, on human health.

RECENT FINDINGS

There is a consensus view that folic acid supplementation has numerous health benefits, many of which are significant in their impact. However, emerging evidence suggests that increased population exposure to folic acid may also have a negative impact with respect to certain developmental and degenerative disorders. As examples, presently much attention is focused on the role of folic acid fortification augmenting colon cancer risk, whereas earlier in the life cycle, the vitamin may additionally influence insulin resistance. Without question, conditions that are influenced by folic acid are both diverse and many - from concerns relating to cognitive decline, breast cancer and vascular disease through to preconceptional issues where maternal folate levels might conceivably alter the phenotype of offspring via epimutations.

SUMMARY

The highly complex and critical biological importance of folic acid-related molecular nutrition makes it a difficult micronutrient to deploy as a simple intervention at a population level - it has far too many biochemical spheres of influence to predict effects in a generalized way. Additionally, several gene variants and other nutrients are interactive factors. It is, therefore, hardly surprising that the scientific community does not have a true consensus view on whether mandatory fortification is appropriate as a population measure. This latter point not withstanding, any ultimate decisions on fortification should be well rooted in scientific fact rather than political expediency.

Two methylenetetrahydrofolate reductase gene (MTHFR) polymorphisms, schizophrenia and bipolar disorder: an association study

Recent meta-analyses of the methylenetetrahydrofolate reductase gene (MTHFR) have suggested association between two of its functional single gene polymorphisms (SNPs; C677T and A1298C) and schizophrenia. Studies have also suggested association between MTHFR C677T and A1298C variation and bipolar disorder. In a replication attempt the MTHFR C677T and A1298C SNPs were analyzed in three Scandinavian schizophrenia case-control samples. In addition, Norwegian patients with bipolar disorder were investigated. There were no statistically significant allele or genotype case-control differences. The present Scandinavian results do not verify previous associations between the putative functional MTHFR gene polymorphisms and schizophrenia or bipolar disorder. However, when combined with previous studies in meta-analyses there is still evidence for association between the MTHFR C677T polymorphism and schizophrenia. Additional studies are warranted to shed further light on these relationships.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

Effect of the methylenetetrahydrofolate reductase gene polymorphisms on homocysteine, folate and vitamin B12 in patients with bipolar disorder and relatives

We investigated the effect of polymorphic variants of c.1298A>C (Glu429Ala) and c.677C>T (Ala222Val) in methylenetetrahydrofolate (MTHFR) gene on the total homocysteine (tHcy), folate and B12 levels in patients with bipolar disorder, first-degree relatives of patients, and controls. The c.677C>T and c.1298A>C polymorphisms in MTHFR were determined by polymerase chain reaction-restriction fragment length polymorphism in 197 bipolar patients, 278 relatives and 238 controls. tHcy and folate and vitamin B12 levels were measured by Fluorescence Polarization Immunoassay and Electrochemiluminescence, respectively. The tHcy was significantly increased in patients and relatives. In contrast, folate and B12 were significantly lower in patients and relatives. Gender was not considered as a significant determinant in the multivariate analysis. Genotypes of c.1298A>C and c.677C>T were correlated with tHcy, folate and B12. Patients and relatives carrying TT and/or AA and AC genotypes had elevated tHcy and reduced folate and B12 levels. High tHcy but low folate and vitamin B12 levels may be a risk factor for development of bipolar disorder.