Glutamate carboxypeptidase II gene polymorphisms and neural tube defects in a high-risk Chinese population

Polymorphism rs1052536 in Base Excision Repair Gene Is a Risk Factor in a High-Risk Area of Neural Tube Defects in China

Background

DNA Base Excision Repair Gene-DNA LigaseIII (LIG3) is an important repair gene in the repair pathway and plays an important role in maintaining the integrity of mitochondria. Rs1052536 and rs3135967 polymorphisms of the gene are associated with lung cancer, keratoconus, and Fuchs endothelial corneal dystrophy. There is no previously published report on the relationship between the polymorphisms and neural tube defects (NTDs).

Material/Methods

Mass ARRAY iPLEX was used to determine the distribution of the polymorphisms in the case group of 108 NTD pregnant women and a control group of 233 normal healthy pregnant women to examine the relevance of their polymorphisms and NTD occurrence.

Results

The homozygotes of rs1052536 TT were associated with an increased risk for NTDs than CC (P=0.014, OR=2.31, 95%CI [1.17–4.54]), and variants of rs1052536 T were associated with an increased risk of NTDs (P=0.024, OR=1.50, 95%CI [1.06–2.13]). The stratified analysis showed that TT genotype of rs1052536 increased the risk of anencephaly (P=0.016, OR=2.69, 95%CI [1.18–6.10]) and the T allele significantly increased the risk of cranial NTDs (P=0.033, OR=1.56, 95%CI [1.04–2.35]).

Conclusions

Rs1052536 in LIG3 gene might be a potential genetic risk factor in a high-risk area of NTDs in China.

A Cross-Sectional Study of Dietary and Genetic Predictors of Blood Folate Levels in Healthy Young Adults

Since 1998, the U.S. has mandated folic acid (FA) fortification of certain grain products to reduce the risk of neural tube defects. Folate intake and red blood cell (RBC) folate concentrations increased substantially post-intervention, although recent studies raise concerns about the level of ongoing benefit. This study investigated blood folate level determinants in healthy young adults, including intake of naturally occurring food folate, synthetic FA, and the interaction of naturally occurring food folate with a common missense variant in the FOLH1 gene thought to affect absorption. Participants (n = 265) completed the Diet History Questionnaire II, RBC folate testing, and were genotyped for the 484T>C FOLH1 variant. Men reported significantly greater intake of all folate sources except for supplemental FA, but RBC folate levels did not significantly differ by sex. Synthetic FA was a stronger predictor of RBC folate than naturally occurring food folate. In the largest racial group, synthetic FA and the interaction of FOLH1 genotype with naturally occurring food folate significantly predicted RBC folate, with the overall model accounting for 13.8% of the variance in RBC folate levels. Blood folate levels rely on a complex interaction of natural and synthetic folate intake as well as FOLH1 genotype.

Biochemical and genetic predictors and correlates of response to lamotrigine and folic acid in bipolar depression: Analysis of the CEQUEL clinical trial

OBJECTIVES

CEQUEL (Comparative Evaluation of QUEtiapine plus Lamotrigine combination versus quetiapine monotherapy [and folic acid versus placebo] in bipolar depression) was a double-blind, randomized, placebo-controlled, parallel group, 2×2 factorial trial that examined the effect of adding lamotrigine and/or folic acid (FA) to quetiapine in bipolar depression. Lamotrigine improved depression, but its effectiveness was reduced by FA. We investigated the baseline predictors and correlates of clinical response, and the possible basis of the interaction.

METHODS

The main outcome was change in depressive symptoms at 12 weeks, measured using the Quick Inventory for Depressive Symptoms-self report version 16 (QIDS-SR16). We examined the relationship between symptoms and lamotrigine levels, and biochemical measures of one-carbon metabolism and functional polymorphisms in catechol-O-methyltransferase (COMT), methylene tetrahydrofolate reductase (MTHFR) and folate hydrolase 1 (FOLH1).

RESULTS

Lamotrigine levels were unaffected by FA and did not differ between those participants who achieved remission and those with persisting symptoms. When participants with subtherapeutic serum levels were excluded, there was a main effect of lamotrigine on the main outcome, although this remained limited to those randomized to FA placebo. None of the biochemical measures correlated with clinical outcome. The negative impact of FA on lamotrigine response was limited to COMT Met carriers. FOLH1 and MTHFR had no effect.

CONCLUSIONS

Our results clarify that FA's inhibition of lamotrigine's efficacy is not a pharmacokinetic effect, and that low serum lamotrigine levels contributed to lamotrigine's lack of a main effect at 12 weeks. We were unable to explain the lamotrigine-FA interaction, but our finding that it is modulated by the COMT genotype provides a starting point for follow-on neurobiological investigations. More broadly, our results highlight the value of including biochemical and genetic indices in randomized clinical trials.

Genetic polymorphisms and folate status

Moderate hyperhomocysteinemia-induced low folate status is an independent risk factor for cardiovascular disease, dementia, and depression. Folate is an essential cofactor in the one-carbon metabolism pathway and is necessary in amino acid metabolism, purine and thymidylate synthesis, and DNA methylation. In the folate cycle and homocysteine metabolism, folate, vitamin B12, vitamin B6, and vitamin B2 are important cofactors. Many enzymes are involved in folate transport and uptake, the folate pathway, and homocysteine (Hcy) metabolism, and various polymorphisms have been documented in these enzymes. Serum folate and total Hcy (tHcy) levels are influenced by folate intake and genetic polymorphisms in 5,10-methylenetertahydrofolate reductase (MTHFR) such as C677T. The prevalence of the MTHFR 677TT genotype varies across ethnic groups and regions, with a frequency of approximately 15% in Japanese populations. Individuals with the TT genotype have significantly higher tHcy levels and lower folate levels in serum than those with the CT and TT genotypes. However, administration of folic acid has been shown to eliminate these differences. Moreover, data have suggested that interventions based on genotype may be effective for motivating individuals to change their lifestyle and improve their nutrition status. Accordingly, in this review, we discuss the effects of MTHFR C677T polymorphisms on serum tHcy and folate levels with folic acid intervention and evaluate approaches for overcoming folic acid deficiency and related symptoms.

Folate Augmentation of Treatment--Evaluation for Depression (FolATED): randomised trial and economic evaluation

BACKGROUND

Folate deficiency is associated with depression. Despite the biological plausibility of a causal link, the evidence that adding folate enhances antidepressant treatment is weak.

OBJECTIVES

(1) Estimate the clinical effectiveness and cost-effectiveness of folic acid as adjunct to antidepressant medication (ADM). (2) Explore whether baseline folate and homocysteine predict response to treatment. (3) Investigate whether response to treatment depends on genetic polymorphisms related to folate metabolism.

DESIGN

FolATED (Folate Augmentation of Treatment - Evaluation for Depression) was a double-blind and placebo-controlled, but otherwise pragmatic, randomised trial including cost-utility analysis. To yield 80% power of detecting standardised difference on the Beck Depression Inventory version 2 (BDI-II) of 0.3 between groups (a 'small' effect), FolATED trialists sought to analyse 358 participants. To allow for an estimated loss of 21% of participants over three time points, we planned to randomise 453.

SETTINGS

Clinical - Three centres in Wales - North East Wales, North West Wales and Swansea. Trial management - North Wales Organisation for Randomised Trials in Health in Bangor University. Biochemical analysis - University Hospital of Wales, Cardiff. Genetic analysis - University of Liverpool.

PARTICIPANTS

Four hundred and seventy-five adult patients presenting to primary or secondary care with confirmed moderate to severe depression for which they were taking or about to start ADM, and able to consent and complete assessments, but not (1) folate deficient, vitamin B12 deficient, or taking folic acid or anticonvulsants; (2) misusing drugs or alcohol, or suffering from psychosis, bipolar disorder, malignancy or other unstable or terminal illness; (3) (planning to become) pregnant; or (4) participating in other clinical research.

INTERVENTIONS

Once a day for 12 weeks experimental participants added 5 mg of folic acid to their ADM, and control participants added an indistinguishable placebo. All participants followed pragmatic management plans initiated by a trial psychiatrist and maintained by their general medical practitioners.

MAIN OUTCOME MEASURES

Assessed at baseline, and 4, 12 and 25 weeks thereafter, and analysed by 'area under curve' (main); by analysis of covariance at each time point (secondary); and by multi-level repeated measures (sensitivity analysis): Mental health - BDI-II (primary), Clinical Global Impression (CGI), Montgomery-Åsberg Depression Rating Scale (MADRS), UKU side effects scale, and Mini International Neuropsychiatric Interview (MINI) suicidality subscale; General health - UK 12-item Short Form Health Survey (SF-12), European Quality of Life scale - 5 Dimensions (EQ-5D); Biochemistry - serum folate, B12, homocysteine; Adherence - Morisky Questionnaire; Economics - resource use.

RESULTS

Folic acid did not significantly improve any of these measures. For example it gained a mean of just 2.9 quality-adjusted life-days [95% confidence interval (CI) from -12.7 to 7.0 days] and saved a mean of just £48 (95% CI from -£292 to £389). In contrast it significantly reduced mental health scores on the SF-12 by 3.0% (95% CI from -5.2% to -0.8%).

CONCLUSIONS

The FolATED trial generated no evidence that folic acid was clinically effective or cost-effective in augmenting ADM. This negative finding is consistent with improving understanding of the one-carbon folate pathway suggesting that methylfolate is a better candidate for augmenting ADM. Hence the findings of FolATED undermine treatment guidelines that advocate folic acid for treating depression, and suggest future trials of methylfolate to augment ADM.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN37558856.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 18, No. 48. See the HTA programme website for further project information.

Geographical and ethnic distribution of single nucleotide polymorphisms within genes of the folate/homocysteine pathway metabolism

High levels of plasma homocysteine are associated with an increased risk of many health conditions influenced by both environmental and genetic factors. The objective of this study was to provide the geographical distribution of folate pathway genetic polymorphisms in Mexico and the comparison with the reported frequencies in different continental populations. This study included the analysis of the genotypic frequencies of eight polymorphisms in genes of the folate/homocysteine metabolic pathway in 1,350 Mestizo and Amerindian subjects from different regions in Mexico and 836 individuals from European, African and Asian populations of the 1,000 Genomes Project. In Mexican Mestizo and Amerindian populations, the MTHFR C677T risk genotype (TT) was highly prevalent (frequency: 25 and 57 %, respectively). In Mestizos, the frequency showed clear regional variation related to ancestry; the Guerrero subpopulation with the highest Amerindian contribution had the highest TT frequency (33 %). The MTHFD1 G1958A AA risk genotype was also enriched in Mexican Mestizos and Amerindians (frequency: 34 and 58 %, respectively), whereas in African and Asian ancestry populations the frequency for AA was low (~4 %). All together risk genotypes showed regional differences, and Sonora had significantly different genetic frequencies compared with the other regions (P value <0.05). Our study illustrates differential geographical distribution of the risk variants in the folate/homocysteine metabolic pathway relative to ethnic background. This work supports that certain areas of the world have increased needs for folic acid and vitamin B supplementation, and this information needs to be considered in public health guidelines and eventually policies.

Association between PTCH1 polymorphisms and risk of neural tube defects in a Chinese population

BACKGROUND

SHH signaling pathway plays an important role in the formation of the neural plate and is involved in the regulation of the dorsoventral (DV) axis of the neural tube. Some neural tube defects (NTDs) may be caused through overactivation of the SHH signaling pathway. The PTCH1 gene, encoding a negative regulator of SHH signaling, affects neural tube closure in animal models. However, in humans, the relationship between single nucleotide polymorphisms (SNPs) of the PTCH1 gene and neural tube defects remains unclear.

METHODS

MassARRAY®GENOTYPER™ was used to genotype 18 SNPs of the PTCH1 gene in 187 NTDs and 212 control samples, to determine whether PTCH1 polymorphisms are related to NTDs. MassARRAY®EpiTYPER™ was performed to assess whether methylation modifications may be associated with SNP genotypes in this Chinese population.

RESULT

Increased risk for spina bifida was observed with the G allele of c.3944C>T and the T allele of c.1729™2350G>A in female patients when compared to the normal control group. High methylation levels were detected in those controls bearing the G allele of c.3944C>T.

CONCLUSION

In summary, polymorphisms of the PTCH1 gene may be genetic predisposing factors for spina bifida in the population studied. In addition, methylation modifications associated with the c.3944C>T polymorphism, may provide protection.

The maternal folate hydrolase gene polymorphism is associated with neural tube defects in a high-risk Chinese population

Folate hydrolase 1 (FOLH1) gene encodes intestinal folate hydrolase, which regulates intestinal absorption of dietary folate. Previous studies on the association between polymorphisms rs202676 and rs61886492 and the risk of neural tube defects (NTDs) were inconclusive. A case-control study of women with NTD-affected pregnancies (n = 160) and controls (n = 320) was conducted in the Chinese population of Lvliang, a high-risk area for NTDs. We genotyped the polymorphic sites rs202676 and rs61886492 and assessed maternal plasma folate and total homocysteine (tHcy). Our results showed that in case group, plasma folate concentrations were 18 % lower compared with those of control group (8.32 vs. 6.79 nmol/L, p = 0.033) and tHcy concentrations were 17 % higher (10.47 vs. 12.65 μmol/L, p = 0.047). Almost all samples had the rs61886492 GG genotype (99.78 %). The result showed that the frequency of GG genotype in rs202676 was significantly higher in group with multiple NTDs than in controls (p = 0.030, OR = 2.157, 95 % CI, 1.06-4.38). The multiple-NTD group showed higher maternal plasma concentrations of tHcy (10.47 vs. 13.96 μmol/L, p = 0.024). The GG genotype of rs202676 had a lower maternal folate and higher tHcy concentrations than other genotypes with no significant differences. The result of structural prediction indicated that this variation might change the spatial structure of the protein. These results suggested that the maternal polymorphism rs202676 was a potential risk factor for multiple NTDs in this Chinese population. The allele G might affect maternal plasma folate and tHcy concentration.