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
Introduction
Schizophrenia is a chronic and disabling mental disorder with a lifetime prevalence of approximately 1% in the global population (Freedman, 2003). Accumulating evidence suggests that both genetic and environmental factors contribute to the etiology of schizophrenia (Burmeister et al., 2008). Although schizophrenia has a high heritability with rates estimated at 80% (Sullivan et al., 2003), there has been no consistent replication found for the schizophrenia candidate genes (Harrison and Weinberger, 2005). Recent genome-wide association (GWA) studies have demonstrated new promising susceptibility genes for schizophrenia (O'Donovan et al., 2008), as well as for other common diseases (Rioux et al., 2007, The Wellcome Trust Case Control Consortium, 2007, Zeggini et al., 2007). Therefore, use of this methodology can be advantageous when trying to detect potential genetic factors responsible for the development of these disorders. In addition, by focusing on the specific molecular pathway related to the pathophysiology of schizophrenia, this may also be useful when trying to identify susceptibility genes that have a mild contribution to the development of the disease (Kirov et al., 2005).
Dysfunction of homocysteine metabolism has been linked to neurodevelopmental disorders, including neural tube defects (NTDs) (Blom et al., 2006, van der Put et al., 1995), schizophrenia (Allen et al., 2008, Muntjewerff et al., 2006), and depression (Lewis et al., 2006), in addition to other diseases and syndromes (Hobbs et al., 2000, Kluijtmans et al., 1996, Qian et al., 2007). Recent studies have also suggested that elevated plasma homocysteine levels are observed in major psychiatric disorders such as schizophrenia and bipolar disorder (Levine et al., 2005). Plasma homocysteine levels affect the intracellular methylation process of DNA, lipids, proteins, and neurotransmitters (Scott and Weir, 1998). Both elevated homocysteine levels along with physiological levels of its oxidized derivatives, such as homocysteic acid and homocysteine sulfinic acid, have been shown to be toxic for neurons and vascular endothelial cells (Zou and Banerjee, 2005). While levels of homocysteine are affected by various genes involved in the homocysteine metabolic pathway and by environmental factors such as folate or vitamin B12 intake (Refsum et al., 2004), methylenetetrahydrofolate reductase (MTHFR) also plays a major role in this pathway. MTHFR converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, which serves as a carbon donor for the methylation of homocysteine, leading to the generation of S-adenosylmethionine (SAM) (Andreoli and Maffei, 1975). SAM is a major source of methyl groups in the brain (Godfrey et al., 1990) and is involved in catechol-O-methyltransferase (COMT) reactions such as the catabolism of serotonin and other catecholamines (Anguelova et al., 2003, Chen et al., 2004). Freeman et al. (1975) reported there is direct evidence linking decreased MTHFR activity to schizophrenia (Freeman et al., 1975). These findings have led to multiple genetic analyses examining the link between the MTHFR gene (gene symbol: MTHFR, GenBank accession number: NM_005957) and schizophrenia.
MTHFR is composed of twelve exons (Fig. 1) and is localized on chromosome 1p36.3 (Goyette et al., 1994). It has been suggested that this may be a susceptibility locus for schizophrenia, bipolar disorder (Kempisty et al., 2007) and major depressive disorder (McGuffin et al., 2005). Two common functional polymorphisms of MTHFR, C677T (rs1801133) and A1298C (rs1801131), are known to cause a decrease of enzyme activity and affect nucleic synthesis and DNA methylation (van der Put et al., 1998). Several studies have confirmed the possible involvement of these SNPs in psychiatric conditions such as schizophrenia (Regland, 2005) and affective disorders (Arinami et al., 1997). Subjects with homozygosity for the 677 T allele have a mild increase in their plasma homocysteine levels, and these subjects have a higher frequency of neural tube deficits and premature cardiovascular disease as compared to other similar genotype carriers (Bakker and Brandjes, 1997, Matsushita et al., 1997). The impact of this polymorphism varies according to environmental factors, such as folate, vitamin B2 or vitamin B12 (Hustad et al., 2000, Refsum et al., 2004, van der Put et al., 1995). Although some studies have reported that carriers of the 677 T allele in MTHFR are associated with an increased risk of schizophrenia (Arinami et al., 1997, Muntjewerff et al., 2005, Sazci et al., 2003), others have shown contradictive results (Kunugi et al., 1998, Vilella et al., 2005, Yu et al., 2004). The association of the MTHFR C677T variant with schizophrenia may be linked to the excitatory amino acids hypothesis or to decreased plasma concentrations of SAM that have been reported in psychiatric disorders (Andreoli and Maffei, 1975). Another functional polymorphism, A1298C, also has been shown to decrease MTHFR activity, although van der Put et al. (1998) have reported finding no significant effect of this variant on the plasma homocysteine levels.
A recent meta-analysis demonstrated an association between elevated homocysteine levels or carriers of the 677 T allele and an increased risk of developing schizophrenia (Allen et al., 2008, Muntjewerff et al., 2006). It has been suggested that potential associations between genetic variation in folate metabolism and psychiatric disorders could be plausible biological explanations for these disorders (Coppen and Bolander-Gouaille, 2005).
Taken together, MTHFR may be related to the development of schizophrenia. Although a number of studies have demonstrated associations between specific polymorphisms of MTHFR and schizophrenia, there have been no gene-based analysis studies. Therefore, it is still difficult to interpret these types of studies due to the inconsistent results that have been derived from some of the confounding factors, such as population stratifications (ethnic or gender differences) and number of samples. In the present study, we conducted an association study between MTHFR and schizophrenia in the Japanese population that was based on the gene-wide approach. In addition, we also performed a meta-analysis on the updated data currently available.
Section snippets
Subjects
The samples for this association study consisted of 696 patients with schizophrenia and 747 control subjects. The confirmation sample set for four SNPs (rs1801133, rs17421511, rs17037396, and rs9651118), which were positively associated with schizophrenia in the haplotypic analysis and the imputation analysis, consisted of 797 patients with schizophrenia and 1025 control subjects. Detailed demographical data are presented in Supplementary Table 1.
All subjects were unrelated to each other and
Results
Regarding quality control, the genotype calls of the duplicated samples showed complete concordance (data not shown), and all genotype frequencies of the tagging SNPs were consistent with the HWE. There were no significant differences between the schizophrenic patients and the control subjects in both allele and genotype distributions without imputed (untyped) SNP (rs17421511) (Table 1). In the haplotypic analysis, a nominally significant association was observed between the haplotypes
Discussion
Even though we applied the gene-based approach in the present study, we could not confirm any significant associations of the MTHFR polymorphisms with schizophrenia. In the association analysis, we examined the SNPs covering the entire gene, including all of the tagging SNPs that had at least ~ 10% MAF listed on the HapMap database. For all of the genoõtyped SNPs, there were no associations noted between the patients with schizophrenia and the controls in any of the allele frequencies after
Role of the funding source
Funding for this study was provided by research grants from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, the Ministry of Health of Japan, Labor and Welfare, Grant-in-Aid for Scientific Research B (No. 22390223) and C (No. 18591309) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, Mext Academic Frontier, the Japan Health Sciences Foundation (Research on Health Sciences focusing on Drug Innovation) and the Core Research for
Contributors
Authors Akira Yoshimi, Nagahide Takahashi, and Toshiya Inada designed the study and wrote the protocol. Authors Akira Yoshimi and Yukiko Kawamura conducted SNPs genotyping and statistical analyses. Authors Norio Ozaki, Yukihiro Noda, and Kiyofumi Yamada managed the literature searches and analyses. Author Akira Yoshimi wrote the first draft of the manuscript and Branko Aleksic revised. All authors contributed to and have approved the final manuscript.
Conflict of interest
The authors have no conflicts to declare.
Acknowledgements
We sincerely thank the patients and healthy volunteers for participation in our study, and Ryoko Ishihara for her technical assistance. This work was supported in part by research grants from the Ministry of Education, Culture, Sports, Science, and Technology of Japan, the Ministry of Health of Japan, Labor and Welfare, Grant-in-Aid for Scientific Research B (No. 22390223) and C (No. 18591309) from the Ministry of Education, Culture, Sports, Science and Technology of Japan, Mext Academic
References (70)
- et al.
Letter: blood-levels of S-adenosylmethionine in schizophrenia
Lancet
(1975) - et al.
Population stratification and spurious allelic association
Lancet
(2003) - et al.
Functional analysis of genetic variation in catechol-O-methyltransferase (COMT): effects on mRNA, protein, and enzyme activity in postmortem human brain
Am. J. Hum. Genet.
(2004) - et al.
Meta-analysis in clinical trials
Control. Clin. Trials
(1986) - et al.
Association of plasma homocysteine and methylenetetrahydrofolate reductase C677T gene variant with schizophrenia: a Chinese Han population-based case–control study
Psychiatry Res.
(2009) - et al.
Meta-analysis in epidemiology, with special reference to studies of the association between exposure to environmental tobacco smoke and lung cancer: a critique
J. Clin. Epidemiol.
(1991) - et al.
Folate, homocysteine, interleukin-6, and tumor necrosis factor alfa levels, but not the methylenetetrahydrofolate reductase C677T polymorphism, are risk factors for schizophrenia
J. Psychiatr. Res.
(2010) - et al.
Enhancement of recovery from psychiatric illness by methylfolate
Lancet
(1990) - et al.
Polymorphisms in genes involved in folate metabolism as maternal risk factors for Down syndrome
Am. J. Hum. Genet.
(2000) - et al.
Association of 677C > T polymorphism of methylenetetrahydrofolate reductase (MTHFR) gene with bipolar disorder and schizophrenia
Neurosci. Lett.
(2006)
Distribution of 1298A > C polymorphism of methylenetetrahydrofolate reductase gene in patients with bipolar disorder and schizophrenia
Eur. Psychiatry
High homocysteine serum levels in young male schizophrenia and bipolar patients and in an animal model
Prog. Neuropsychopharmacol. Biol. Psychiatry
The frequency of the methylenetetrahydrofolate reductase-gene mutation varies with age in the normal population
Am. J. Hum. Genet.
Meta-analysis of genetic association studies
Trends Genet.
PLINK: a tool set for whole-genome association and population-based linkage analyses
Am. J. Hum. Genet.
Schizophrenia and single-carbon metabolism
Prog. Neuropsychopharmacol. Biol. Psychiatry
Methylenetetrahydrofolate reductase gene polymorphisms in patients with schizophrenia
Brain Res. Mol. Brain Res.
Association of the C677T and A1298C polymorphisms of methylenetetrahydrofolate reductase gene with schizophrenia: association is significant in men but not in women
Prog. Neuropsychopharmacol. Biol. Psychiatry
Support for association of schizophrenia with genetic variation in the 6p22.3 gene, dysbindin, in sib-pair families with linkage and in an additional sample of triad families
Am. J. Hum. Genet.
A highly significant association between a COMT haplotype and schizophrenia
Am. J. Hum. Genet.
Mutated methylenetetrahydrofolate reductase as a risk factor for spina bifida
Lancet
A second common mutation in the methylenetetrahydrofolate reductase gene: an additional risk factor for neural-tube defects?
Am. J. Hum. Genet.
Further evidence that hyperhomocysteinemia and methylenetetrahydrofolate reductase C677T and A1289C polymorphisms are not risk factors for schizophrenia
Prog. Neuropsychopharmacol. Biol. Psychiatry
The interpretation of random-effects meta-analysis in decision models
Med. Decis. Making
A method and server for predicting damaging missense mutations
Nat. Methods
Systematic meta-analyses and field synopsis of genetic association studies in schizophrenia: the SzGene database
Nat. Genet.
A systematic review of association studies investigating genes coding for serotonin receptors and the serotonin transporter: II. Suicidal behavior
Mol. Psychiatry
Methylenetetrahydrofolate reductase variant and schizophrenia/depression
Am. J. Med. Genet.
Hyperhomocysteinaemia and associated disease
Pharm. World Sci.
Case–control association study of 59 candidate genes reveals the DRD2 SNP rs6277 (C957T) as the only susceptibility factor for schizophrenia in the Bulgarian population
J. Hum. Genet.
Neural tube defects and folate: case far from closed
Nat. Rev. Neurosci.
Deconstructing schizophrenia: an overview of the use of endophenotypes in order to understand a complex disorder
Schizophr. Bull.
Psychiatric genetics: progress amid controversy
Nat. Rev. Genet.
Population genetics—making sense out of sequence
Nat. Genet.
Treatment of depression: time to consider folic acid and vitamin B12
J. Psychopharmacol.
Cited by (31)
Association study of methylenetetrahydrofolate reductase genetic polymorphism 677C>T with schizophrenia in hospitalized patients in population of European Russia
2018, Asian Journal of PsychiatryCitation Excerpt :But later Saetre et al. (2012) in a larger study of “northern” population reported a different result: polymorphism MTHFR677C>T did not affect the age at onset of schizophrenia (n = 2198, not specified whether in- or outpatients). Yoshimi et al. (2010) got conflicting results and reported that further research was needed in this area (patients with schizophrenia = 696, control subjects = 747). Thus, a lot of unclear issues remain in the investigation of MTHFR 677C>T polymorphism association with schizophrenia.
Role of MTHFR C677T gene polymorphism in the susceptibility of schizophrenia: An updated meta-analysis
2016, Asian Journal of PsychiatryMethylenetetrahydrofolate reductase (MTHFR) C677T polymorphism: Epidemiology, metabolism and the associated diseases
2015, European Journal of Medical GeneticsSpecific and common genes implicated across major mental disorders: A review of meta-analysis studies
2015, Journal of Psychiatric ResearchCitation Excerpt :For the other MTHFR variant (A1298C), five studies supported the role of the C allele or CC genotype in SZ in mixed (Shi et al., 2008b; Zintzaras, 2006), Asian (Kim et al., 2011), or Caucasian cohorts (Allen et al., 2008; Gilbody et al., 2006; Shi et al., 2008b) (Supplementary Table 1). The role of the C allele in mixed ethnic cohorts was conflicted by null effects reported by three studies (Supplementary Table 3), one of which was in a larger cohort (Peerbooms et al., 2011) than the confirmed study (Shi et al., 2008b); the other two conflicting studies did not report total sample size (Kim et al., 2011; Yoshimi et al., 2010), so the reasons for this discrepancy is not definitive. The role of C allele was also conflicted by null effects reported by three studies in Caucasian cohorts (Supplementary Table 3); in this case, the conflicting null study used a smaller cohort (Zintzaras, 2006) than the confirmed study (Shi et al., 2008b), and the other two studies again failed to report total sample size (Kim et al., 2011; Yoshimi et al., 2010) so the reason for the discrepancy is unclear.
B vitamin polymorphisms and behavior: Evidence of associations with neurodevelopment, depression, schizophrenia, bipolar disorder and cognitive decline
2014, Neuroscience and Biobehavioral ReviewsMeta-analysis of MTHFR gene variants in schizophrenia, bipolar disorder and unipolar depressive disorder: Evidence for a common genetic vulnerability?
2011, Brain, Behavior, and ImmunityCitation Excerpt :Fifth, the generalizability of the present meta-analysis is limited to the ethnic groups investigated, i.e. White and Asian. In line with the current results, the meta-analysis of Yoshimi et al. (2010) supported an association between MTHFR C677T with schizophrenia (Yoshimi et al., 2010), similar to earlier meta-analyses (Yoshimi: random effects OR = 1.17, 95% CI: 1.07–1.29) (Allen et al., 2008; Gilbody et al., 2007; Jonsson et al., 2008; Lewis et al., 2005; Muntjewerff et al., 2006; Shi et al., 2008; Zintzaras, 2006). Regarding MTHFR A1298C, Zintzaras (2006) concluded in his meta-analysis on 2.565 subjects that this SNP was associated with the diagnosis of schizophrenia, however not in all genetic models examined (fixed effects ORCvA = 1.16, 95% CI: 1.03–1.31; ORAC/CCvAA = 1.19, 95% CI: 1.02–1.40; OR CCvAA = 1.37, 95% CI 1.03–1.82; random effects OR CCvAC/AA = 1.33, 95% CI: 0.94–1.88) (Zintzaras, 2006).