ABSTRACT
Neural tube defects (NTD) are likely to result from an interaction of several genes and environmental factors. Because periconceptional folate intake reduces the NTD risk in the fetus, and because mothers of children with NTD showed elevated plasma homocysteine levels, gene polymorphisms of the folate and homocysteine pathway, such as 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C-->T, MTHFR 1298A-->C and cystathionine beta-synthase (CBS) 844ins68, have been implicated in the etiology of NTD. Several studies have demonstrated that these polymorphisms may indeed be associated with NTD in some populations. In order to evaluate the role of these polymorphisms and their interaction in NTD, we genotyped 417 individuals for case-control studies and 129 families for transmission disequilibrium tests. We are the first to present detailed data on MTHFR haploid genotypes in combination with CBS 844ins68. The MTHFR risk genotype 677CT/1298AC, known to be associated with decreased enzyme activity and increased homocysteine, was found significantly more often in patients than in controls (P = 0.02). A CBS insertion allele in addition to MTHFR 677CT/ 1298AC heterozygosity or MTHFR 677TT/1298AA homozygosity did not result in an increased risk for NTD. This is in agreement with the recently reported homocysteine-lowering effect of the CBS 844ins68 allele in carriers of MTHFR variants.
Subject(s)
Folic Acid/metabolism , Homocysteine/metabolism , Neural Tube Defects/genetics , Neural Tube Defects/metabolism , Alleles , Case-Control Studies , Cystathionine beta-Synthase/genetics , Female , Gene Frequency , Genotype , Germany , Humans , Male , Methylenetetrahydrofolate Reductase (NADPH2) , Neural Tube Defects/etiology , Oxidoreductases Acting on CH-NH Group Donors/genetics , Polymorphism, Genetic , Risk FactorsABSTRACT
BACKGROUND: Very little is known about the identity of genetic factors involved in the complex etiology of nonsyndromic neural tube defects (NTD). Potential susceptibility genes have emerged from the vast number of mutant mouse strains displaying NTD. Reasonable candidates are the human homologues of mice exencephaly genes Tfap2alpha and Msx2, which are expressed in the developing neural tube. METHODS: A single-strand conformation analysis (SSCA) mutation screen of the coding sequences of TFAP2alpha and MSX2 was performed for 204 nonsyndromic NTD patients including cases of anencephaly (n = 10), encephalocele (n = 8), and spina bifida aperta, SBA (n = 183). A selected number of SBA patients was additionally tested for specific mutations in MTHFD, FRalpha, and PAX1 already shown to be related to NTD. RESULTS: Two TFAP2alpha point mutations in individual SBA patients were silent on the amino acid level (C308C, T396T). On nucleic acid level, these mutations change evolutionary conserved codons and thus may influence mRNA processing and translation efficiency. One SBA patient displayed an exonic 9-bp deletion in MSX2 leading to a shortened and possibly less functional protein. None of these mutations was found in 222 controls. Seven polymorphisms detected in TFAP2alpha and MSX2 were equally distributed in patients and controls. Patients with combined heterozygosity of an exonic MSX2 and an intronic TFAP2alpha polymorphism were at a slightly increased risk of NTD (OR 1.71; 95% CI 0.57-5.39). CONCLUSIONS: Although several new genetic variants were found in TFAP2 and MSX2, no statistically significant association was found between NTD cases and the new alleles or their combinations. Further studies are necessary to finally decide if these gene variants may have acted as susceptibility factors in our individual cases.
Subject(s)
DNA-Binding Proteins/genetics , Mutation , Neural Tube Defects/genetics , Receptors, Cell Surface , Transcription Factors/genetics , Alleles , Anencephaly/genetics , Animals , Base Sequence , Carrier Proteins/genetics , Codon , DNA, Complementary/metabolism , Encephalocele/genetics , Exons , Folate Receptors, GPI-Anchored , Folic Acid/metabolism , Gene Deletion , Genotype , Homeodomain Proteins , Humans , Mice , Molecular Sequence Data , Pedigree , Point Mutation , Polymorphism, Genetic , Polymorphism, Single-Stranded Conformational , Spinal Dysraphism/genetics , Transcription Factor AP-2ABSTRACT
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.