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

Early-Onset Schizophrenia: A Special Phenotype of the Disease Characterized by Increased MTHFR Polymorphisms and Aggravating Symptoms

BACKGROUND

Patients with early-onset schizophrenia usually exhibit more severe symptoms, revealing a potentially distinctive disease phenotype. Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in folate conversion and methylation modification associated with the disease. We aimed to investigate the potential effects of MTHFR polymorphisms and related methylation patterns in patients with early-onset schizophrenia, which implies special phenotypes of schizophrenia.

METHODS

In 177 patients with schizophrenia, MTHFR polymorphism at three sites (C677T, A1298C, and G1793A) and the Positive and Negative Syndrome Scale (PANSS) were tested. Differential methylation positions (DMPs) and enrichment of genes and related pathways were analyzed by testing the genomic methylation level. Catechol-O-methyltransferase (COMT), solute carrier family 6 member 4 (SLC6A4), neuregulin1 (NRG1), and brain-derived neurotrophic factor (BDNF) were selected to evaluate the methylation levels of specific CpG regions by pyrosequencing.

RESULTS

Higher levels of symptom severity and MTHFR polymorphisms and lower levels of global DNA methylation in patients with early-onset schizophrenia were observed in this study. SLC6A4 was hypermethylated, and BDNF was hypomethylated in specific regions of patients with early-onset schizophrenia.

CONCLUSION

Aggravating symptoms, increased MTHFR polymorphisms, and reduced genomic methylation levels may be characteristics and underlying mechanisms of early-onset schizophrenia, which implies a special disease phenotype. Beyond that, specific genes and biological pathways may imply the potential phenotype of schizophrenia.

Methylenetetrahydrofolate reductase and psychiatric diseases

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme for the critical process of one-carbon metabolism involving folate and homocysteine metabolisms. It is known that some polymorphism of MTHFR would result in reduction of MTHFR enzyme activity as well as DNA methylation process, later shown to have significant impacts in various psychiatric diseases. However, it is unclear whether the polymorphism of MTHFR could be an independent or an add-on risk factor for specific psychiatric symptoms, such as anxiety, depression, positive, or negative symptoms of schizophrenia, or acts as risk factor for specific psychiatric disorders, such as schizophrenia, major depression, autisms, and bipolar disorders. It is also understudied on whether folate supplements could be an effective treatment for psychiatric patients with defect MTHFR activity. In this review, we not only gathered the most recent discoveries on MTHFR polymorphism and related DNA methylation in various psychiatric disorders, but also highlighted the potential relationships between MTHFR activity and implication of folate-related function in specific mental diseases.

Advanced paternal age is associated with earlier schizophrenia onset in offspring. Results from the national multicentric FACE-SZ cohort

The association between advanced paternal age (APA) and increased risk of schizophrenia (SZ) is well established. The objectives of the present study were to further determine if SZ participants with APA (APA+), versus those without (APA-), had: (i) different illness characteristics; (ii) different responses to antipsychotic medication; and (iii) different cognitive characteristics. Participants were a non-selected representative multicentric sample of stabilized community-dwelling people diagnosed with SZ included in the FACE-SZ cohort. 389 participants (73% males, mean aged 32.7 years, mean illness duration 10.8 years) formed the study sample, with each comprehensively evaluated, clinically and neuropsychologically, over 2 days. 118 participants (30.3%) were defined as APA+ according to their father's age at birth (≥35 years). APA+ was associated with a wide range of cognitive dysfunctions in univariate analyses. In multivariate analyses, the only significant difference was the age at onset, with a mean 1.6 year earlier in APA+, compared to APA- (20.7 vs. 22.3 years; p=0.02). This difference is independent of sociodemographic characteristics and I.Q. No association with clinical symptomatology and treatment response was found. The present study supports the neomutation hypothesis and confirms APA as a relevant clinical variable to discriminate potential schizophrenia subtypes. Potential underlying pathophysiological mechanisms are discussed.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: epidemiology, metabolism and the associated diseases

The Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism is associated with various diseases (vascular, cancers, neurology, diabetes, psoriasis, etc) with the epidemiology of the polymorphism of the C677T that varies dependent on the geography and ethnicity. The 5,10-Methylenetetrahydrofolate reductase (MTHFR) locus is mapped on chromosome 1 at the end of the short arm (1p36.6). This enzyme is important for the folate metabolism which is an integral process for cell metabolism in the DNA, RNA and protein methylation. The mutation of the MTHFR gene which causes the C677T polymorphism is located at exon 4 which results in the conversion of valine to alanine at codon 222, a common polymorphism that reduces the activity of this enzyme. The homozygous mutated subjects have higher homocysteine levels while the heterozygous mutated subjects have mildly raised homocysteine levels compared with the normal, non-mutated controls. Hyperhomocysteinemia is an emerging risk factor for various cardiovascular diseases and with the increasing significance of this polymorphism in view of the morbidity and mortality impact on the patients, further prevention strategies and nutritional recommendations with the supplementation of vitamin B12 and folic acid which reduces plasma homocysteine level would be necessary as part of future health education. This literature review therefore focuses on the recent evidence-based reports on the associations of the MTHFR C677T polymorphism and the various diseases globally.

Elevated homocysteine level in first-episode schizophrenia patients--the relevance of family history of schizophrenia and lifetime diagnosis of cannabis abuse

Accumulating evidence indicates that elevated homocysteine (Hcy) level occurs in first-episode schizophrenia (FES) patients. We included 56 FES patients and 53 healthy controls (HC). Plasma level of Hcy was significantly higher in FES patients than HC (p = 0.044). In addition, plasma levels of high-density lipoproteins (HDL) and folate were significantly lower in FES than in HC (p < 0.001). Positive family history of schizophrenia was associated with lower plasma HDL (p = 0.041) and vitamin B12 (p = 0.017), as well as higher level of Hcy (p = 0.017). Patients with FES, who abused cannabis, had higher levels of Hcy (p = 0.017), as well as lower levels of vitamin B12 (p = 0.017) and HDL (p = 0.041). Plasma Hcy negatively correlated with duration of untreated psychosis (r = -0.272, p = 0.042). There was a positive correlation between Hcy level and the severity of negative symptoms (r = 0.363, p = 0.006) and general psychopathology (r = 0.349, p = 0.008) assessed using Positive and Negative Syndrome Scale (PANSS). Vitamin B12 level was negatively associated with the severity of negative symptoms (r = -0.406, p = 0.002), while folate level negatively correlated with general psychopathology score (r = -0.365, p = 0.006) in PANSS. These results indicate that the severity of one-carbon metabolism alterations and HDL deficiency might be associated with family history of schizophrenia and cannabis abuse. Lower vitamin B12 and folate along with elevated Hcy may influence the severity of FES psychopathology.

MTHFR gene polymorphism and age of onset of schizophrenia and bipolar disorder

Objective. Several studies with contradictory results from different cultures about association of methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism in schizophrenia and bipolar disorders. Little is known about this association in Arab culture and Egypt. So the present study aimed to assess the association of MTHFR C677T polymorphism in bipolar disorder (BD) and schizophrenia in comparison to control group. The association between MTHFR C677T polymorphism and the age at onset in schizophrenia or BD was also studied. Methods. Polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) were used to examine the genotype and allele frequencies of MTHFR C677T polymorphism in 149 healthy subjects and 134 bipolar and 103 schizophrenia patients. Results. In BD and schizophrenia, there was a higher prevalence of MTHFR C677T polymorphism than healthy subjects. Earlier age at onset was found in patients with BD, carrying one copy of the T allele or CT genotypes but not in patients with schizophrenia. Conclusion. The present findings suggest that the MTHFR C677T polymorphisms are likely to be associated with the risk of developing BD and schizophrenia and influence the age at onset of BD but not the age at onset of schizophrenia.

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.

Elevated homocysteine level in siblings of patients with schizophrenia

Increased homocysteine plasma levels were reported in patients with schizophrenia and Levine et al. (2002) suggested that such increase characterizes mainly males. In the following study we examined whether such increased levels also characterize male siblings of schizophrenia patients. Forty-four pairs of schizophrenia patients and their corresponding healthy male siblings were recruited and sampled for homocysteine. We also had age-matched controls for each of the sibling. The median homocysteine plasma level for patients was 13.0 µMol/L and 11.7 µMol/L for their male siblings compared with a median of 10.9 µMol/L for the siblings' controls. There was no significant difference between homocysteine plasma level in patients and their siblings. Significant difference was found for homocysteine plasma level between the siblings' group and their matched controls. A partial correlation of Ln plasma homocysteine level between patients and their siblings was found to be close to a zero correlation of -0.089, p=0.57 for the whole study group and -0.15, p=0.38 in the male-male patient-sibling pairs. Our results show that elevated homocysteine plasma level may characterize schizophrenia patients' male siblings, a finding that seems to agree with previous studies suggesting elevated homocysteine level as a risk factor for developing schizophrenia.

Neurocognitive function in long-term treated schizophrenia: a five-year follow-up study

Neurocognitive deficits are a core feature of schizophrenia. Deficits covering a wide range of functions have been well documented. However there is still a lack of longitudinal studies regarding the development of neurocognitive impairment. The current study examined the effect of time in long-term treated patients with schizophrenia and healthy controls on cognitive functions. A neurocognitive test-battery was administered to 36 patients and 46 controls on two occasions with approximately 4.5 years interval. Patients performed significantly worse on all measures on both occasions. The only significant decline over time was the ability to shift mental set between different rules or categories (measured by Trail Making Test B). This decline was present in both patients and controls. Improvement on attention (tested by Continuous Performance Test) was found in patients only and improvement on verbal learning (tested by Rey Auditory Verbal Learning Test) was found only in controls. Education was significantly related to outcome in patients and age was related to outcome in controls. We conclude that neurocognitive function is relatively stable over 4.5 years in patients with long-term treated schizophrenia, in line with previous scientific research. The authors discuss the impact of age and education and limitations of the study.

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and age at onset of schizophrenia: no consistent evidence for an association in the Nordic population

Methylenetetrahydrofolate reductase (MTHFR) is an enzyme involved in metabolic pathways of importance for nucleotide synthesis and methylation of DNA, membranes, proteins and lipids. The MTHFR gene includes a common polymorphism (rs1801133 or C677T), which is associated with enzyme activity. The T-allele of the C677T polymorphism has been associated with earlier age at onset of schizophrenia in a Scandinavian population, although no association was found in replication attempts in other populations. Extending the study to five Nordic samples consisting of 2,198 patients with schizophrenia, including the original Scandinavian samples, there was no significant association between MTHFR C677T polymorphism and age at onset in schizophrenia. The present results do not suggest that the investigated MTHFR polymorphism has any significant influence on age at onset of schizophrenia in the Nordic population.

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.

Is C677T polymorphism in methylenetetrahydrofolate reductase gene a risk factor for diabetic nephropathy or diabetes mellitus in a Chinese population?

BACKGROUND AND AIMS

To date, case-control studies on the association between C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR) gene and diabetes mellitus (DM) or diabetic nephropathy (DN) in different populations have provided inconclusive results. To clarify the effect of the C677T polymorphism on the risk of both DM and DN in a Chinese population, a meta-analysis was performed.

METHODS

A comprehensive literature search was conducted to collect data from all case-control observational studies that investigated association of C677T polymorphism in MTHFR gene with DM or DN in a Chinese population.

RESULTS

Overall, 12 studies in a Chinese population published up to 2011 were combined, and the heterogeneity among them varied from none to moderate. The 677T allele showed significant association with DN (OR = 1.97, 95% CI [1.71, 2.28], p <0.00001), but no relationship with DM (OR = 1.03, 95% CI [0.89, 1.18], p = 0.70) compared with the 677C allele in a Chinese population. Similarly, evidence of significant association with DN was detected in the additive model, the recessive model and the dominant model for allele T (additive model: OR = 3.26, 95% CI [2.46, 4.31], p <0.00001; recessive model: OR = 2.32, 95% CI [1.81, 2.97], p <0.00001; dominant model: OR = 2.35, 95% CI [1.89, 2.91], p <0.00001); however, no relationship with DM was found (additive model: OR = 1.01, 95% CI [0.76, 1.35], p = 0.94; recessive model: OR = 0.98, 95% CI [0.76, 1.26], p = 0.87; dominant model: OR = 1.23, 95% CI [0.91, 1.65], p = 0.18). There were no sources of bias in the selected studies, and the sensitivity analysis (exclusion of studies not in Hardy-Weinberg equilibrium) suggested stability of this meta-analysis.

CONCLUSIONS

C677T polymorphism in MTHFR gene may be a risk factor for DN, but not for DM, in a Chinese population.