Analysis of the MTHFR 1298A-->C and 677C-->T polymorphisms as risk factors for neural tube defects

The thermolabile variant (677TT) of methylenetetrahydrofolate reductase (MTHFR) is a known risk factor for neural tube defects (NTDs). The relationship between a second MTHFR polymorphism (1298A→C) and NTD risk has been inconsistent between studies. We genotyped 276 complete NTD triads (mother, father and child affected with an NTD) and 256 controls for MTHFR 1298A→C. Our findings do not support a role for the 1298A→C polymorphism in NTDs (OR 0.85 (95% CI 0.49–1.47), p= 0.55), nor do we observe a combined effect with the 677C→T polymorphism. Electronic Publication     

Study of MTHFR and MS polymorphisms as risk factors for NTD in the Italian population

 Homozygosity for the C677T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is a risk factor for neural tube defects (NTDs) in many populations, including Italians. Another common mutation on the MTHFR gene, A1298C, has also been described as a risk mutation. Furthermore, several studies have suggested that a defective methionine synthase (MS) enzyme could be a critical defect in folate-related NTDs. An A-to-G transition at bp 2756 on the MS gene has also been reported. In this case-control study, we studied the frequencies of these two polymorphisms in 203 Italian probands with non-syndromic NTDs: 98 mothers, 67 fathers, and 210 control individuals. Although the A1298C polymorphism is common in the Italian population (0.25), the allelic frequency was significantly higher among NTD cases and their parents. Heterozygous patients and mothers have an odds ratio (OR) of 1.98 and 2.11, respectively. The risk associated with the 1298CC genotype was higher for cases (OR = 3.67), for fathers (OR = 3.28), and, above all, for mothers (OR = 6.23). The prevalence of the A2756G polymorphism of the MS gene was determined (0.15). No increased prevalence of the mutated G allele was found in NTD families. This study shows that the MTHFR A1298C polymorphism is a genetic determinant for NTD risk in Italy. No association between the MS A2756G and NTD susceptibility was found. Received: January 17, 2002 / Accepted: March 8, 2002     

Association of methylenetetrahydrofolate reductase (MTHFR) polymorphisms with genetic susceptibility to gastric cancer: a meta-analysis

To clarify the influence of MTHFR C677T and A1298C polymorphisms on gastric cancer (GC), a meta-analysis of eight case-control studies (1,584/2,785 cases/controls) was carried out. Overall, there was moderate heterogeneity among studies, and the C677T allele T was associated with a 27% increased risk of GC compared with C allele: the random effects (RE) OR (95% confidence interval in parenthesis) was significant [OR=1.27 (1.13–1.44)]. In East Asians, the association was significant: RE OR=1.28 (1.14–1.44), whereas, in Caucasians it was not significant. Regarding gastric cancer adenocarcinoma (GCA), an association for the allele contrast in East Asians was detected: fixed effects (FE) OR=1.36 (1.18–1.56). The recessive model for allele T produced significant results overall and in East Asians for GC [FE OR=1.47 (1.26–1.72) and FE OR=1.61 (1.32–1.96), respectively] and for GCA [RE OR=1.53 (1.13–2.05) and FE OR=1.70 (1.36–2.12)]. The A1298C polymorphism was associated with GCA in East Asians: the FE OR for the allele contrast (C vs. A) was 1.38 (1.18–1.62), and under a recessive model for allele C, OR=1.62 (1.28–2.06). There were no sources of bias in the selected studies; the differential magnitude of effect in large versus small studies was not significant. In conclusion, there is evidence of association between MTHFR polymorphisms and GC, mainly in East Asians.     

High prevalence of the thermolabile methylenetetrahydrofolate reductase variant in Mexico: a country with a very high prevalence of neural tube defects

Neural tube defects (NTD) are highly prevalent in the Mexican population. According to data from the Registry and Epidemiological Surveillance of External Congenital Malformations (RYVEMCE), at least 1 in 250 conceptions that reach 20 weeks of pregnancy or more has a NTD. This number is three to four times higher than that observed in other related ethnic groups. A common novel mutation (C677T) in the methylenetetrahydrofolate reductase (MTHFR) gene is considered an associated risk factor for NTD and other malformations. Studies in different populations agree that the prevalence of the homozygote for the mutated allele is higher in cases of NTD than in controls. In a meta-analysis recently published, the mean prevalence of the homozygote for the mutation was 9.2% for different groups of European controls and 16.4% in NTD cases from the same populations. This prompted us to investigate the frequency of the normal (C) and the mutant (T) alleles and the prevalence of the expected (CC, CT and TT) genotypes in 250 healthy Mexican women from different parts of the country. The proportion of CC (17.6%), CT (47.6%), and TT (34. 8%) genotypes found, and the gene frequencies of 0.414 and 0.586% for the C and T alleles, respectively, confirmed the very high prevalence of the mutant allele and the TT genotype in the sample studied. Comparisons with studies done in Holland, Ireland, the United States, Japan, and other ethnic groups showed highly significant differences, with an average OR of 5.8 (95% Cl 3.4-10.3) for a Mexican being homozygous for the mutation. These findings may explain an important part of the high prevalence of NTD observed in our population.     

Frequency of the thermolabile variant C677T in the MTHFR gene and lack of association with neural tube defects in the State of Yucatan,Mexico

The C677T variant in the MTHFR gene is considered to be an associated risk factor for neural tube defects. However, the association has not been found in some ethnic groups. In order to assess the association between neural tube defects and the C677T variant, we determined the frequency of this variant in the MTHFR gene in the State of Yucatan, Mexico, where neural tube defects are highly prevalent. The study was performed on 65 subjects with spine bifida, 60 of their mothers and 110 control subjects. The presence of the C677T variant was determined by amplification and digestion with HinF1 of each subject's DNA. Genotypic and allelic frequencies were calculated for all groups. We did not observe any statistically significant difference in the genotypic or allelic frequencies between cases and controls for any of the groups studied (p > 0.05), suggesting that the thermolabile variant C677T is not an associated risk factor neither for the development of neural tube defects nor for mothers to have affected offspring in the population from Yucatan. Interestingly, the frequency of the C677T variant (54%) obtained in the Yucatan population is one of the highest reported (p < 0.01) and confirmed the high frequency of this allele throughout Mexico.     

Linkage disequilibrium of MTHFR genotypes 677C/T-1298A/C in the German population and association studies in probands with neural tube defects(NTD)

A number of studies have demonstrated that the common polymorphism 677C→T in the gene encoding 5, 10-methylenetetrahydrofolate reductase (MTHFR) leads to a thermolabile variant with decreased enzyme activity and to mildly elevated plasma homocysteine. 677TT homozygosity was shown to be more frequent in NTD probands compared with controls in some studies. Recently, another polymorphism, 1298A→C, in the MTHFR gene was described and combined heterozygosity 677CT/1298AC was suggested to be an additional risk factor for NTD. The present study examines the genotype and haplotype distribution of the two polymorphisms in the German population and evaluates the impact on NTD individuals and their relatives. To determine the haplotype of all individuals tested, we developed an easy-to-perform ARMS-RFLP test. Our data show that the two polymorphisms are in linkage disequilibrium in the general population and in NTD individuals. There was no statistically significant difference in allele and genotype frequency between probands (patients, fetuses) and controls (P > 0.10) and between observed and expected values for mother–child pairs (P > 0.80). Taking into account gender, an increased rate of 677CT heterozygotes was found in affected and unaffected males compared to affected and unaffected females. A family-based association study using a multiallelic transmission disequilibrium test (TDT) also shows that transmission rates do not deviate significantly from equilibrium (P > 0.50). Thus, our data provide no evidence for an association between NTD phenotype and MTHFR 677C/T-1298A/C genotypes and haplotypes. Am. J. Med. Genet. 87:23–29, 1999. © 1999 Wiley-Liss, Inc.     

Genotype and haplotype distributions of <Emphasis Type="Italic">MTHFR </Emphasis>677C>T and 1298A>C single nucleotide polymorphisms: a meta-analysis

 Common single nucleotide polymorphisms (SNPs; 677C>T and 1298A>C) in the methylenetetrahydrofolate reductase gene (MTHFR) decrease the activity of the enzyme, leading to hyperhomocysteinemia, particularly in folate-deficient states. We calculate herein the haplotype frequencies of the MTHFR 677 and 1298 polymorphisms in pooled general populations derived from published data. We selected 16 articles that provided reliable data on combined MTHFR genotypes in general populations (n = 5389). The combined data comprised the following totals for each genotype at nucleotide positions 677 and 1298: 838 CC/AA (i.e., 677CC/1298AA), 1225 CC/AC, 489 CC/CC, 1120 CT/AA, 1093 CT/AC, 8 CT/CC, 606 TT/AA, 10 TT/AC, and 0 TT/CC. The estimated haplotype frequencies, and the fractional contribution of each, were 677C/1298A, 0.37; 677C/1298C, 0.31; 677T/1298A, 0.32; and 677T/1298C, 0.0023 to 0.0034. Thus, a vast majority of 677T alleles and 1298C alleles are associated with 1298A alleles and 677C alleles, respectively. There may be an increased frequency of the very rare cis 677T/1298C haplotype in some parts of the United Kingdom and Canada, possibly due to a founder effect. Further studies on both SNPs are needed to determine their exact role in various clinical settings. Received: August 22, 2002 / Accepted: October 7, 2002 Correspondence to:S. Ogino     

孕中期产前筛查11716例分析

目的评价妊娠中期（AFP/β-hCG）唐氏综合征/神经管缺陷产前筛查系统产前筛查唐氏综合征和神经管缺陷的临床应用价值。方法采用酶联免疫分析11716例孕龄为14-20周,年龄为20-45岁妊娠妇女AFP/β-hCG,并结合孕妇年龄、孕周等其它因素,用唐氏综合征产前筛查风险估算和管理软件综合评价孕中期妇女妊娠唐氏综合征和神经管缺陷的风险度。结果检出唐氏综合征高危妊娠650例,筛查阳性率为5.54%,经过羊水染色体核型分析、出生缺陷监测和新生儿外周血染色体核型分析,共筛查出16例唐氏综合征患儿,而在低高危妊娠中发现1例唐氏综合征患儿。检出神经管缺陷高危妊娠60例,筛查阳性率为0.51%,均经过B超检查,共检出20例神经管缺陷胎儿;在11656例神经管缺陷低危妊娠中,未发现神经管缺陷患儿。结论AFP/β-hCG产前筛查扩大了孕妇人群,提高了唐氏综合征和神经管缺陷患儿的检出率,最大可能避免了这些缺陷儿的出生,同时也减少了因唐氏综合征和神经管缺陷导致的围产儿死亡,具有明显的经济效益和社会效益,也是落实优生优育政策非常有效的技术手段。     

PRKCI基因单核苷酸多态性与神经管畸形的相关性研究

目的探讨PRKCI基因单核苷酸多态性（SNP）与中国山西省神经管畸形（NTDs）发生的相关性。方法采用病例对照研究,利用MassARRAY分子量阵列分析平台,检测133例NTDs标本和135例非病理性胎儿标本PRKCI基因中17个标签SNPs的基因分型,分析其与NTDs发生的相关性。结果 17个SNPs位点中,16个的微效等位基因频率（MAF）与HapMap或dbSNP数据库的结果基本一致。除rs9876082外,其余SNPs位点的基因型分布和等位基因频率在病例组和对照组均无明显差异。rs9876082位点为纯合的微效等位基因A时,NTDs的发病率增加（P=0.035,比值比=2.135,95%可信区间=1.846-2.471）,但是调整其它变量后进行logistic回归分析,这种相关性不再明显（P=0.057）。结论 PRKCI基因rs9876082位点与NTDs的发生有弱的相关性,这种相关性需进一步加大样本进行验证,PRKCI基因可能不是通过其SNPs影响NTDs的易感性。     

Possible interaction of genotypes at cystathionine β-synthase and methylenetetrahydrofolate reductase (MTHFR) in neural tube defects

Neural tube defects are a common, complex disorder with genetic and environmental components to risk. We investigated the previously reported interaction between homozygosity for the thermolabile variant at the methylenetetrahydrofolate reductase and heterozygosity for the 844ins68 allele at the cystathionine beta-synthase loci in cases with lumbosacral myelomeningocele and their parents. Using control allele frequencies from our sample pooled with those published in the literature, we confirm a marginally significant interaction at these two loci. This finding suggests that additional, larger studies are warranted to investigate this possible interaction in more detail.