Neural Tube Defects and Folate Pathway Genes: Family-Based Association Tests of Gene–Gene and Gene–Environment Interactions

BACKGROUND: Folate metabolism pathway genes have been examined for association with neural tube defects (NTDs) because folic acid supplementation reduces the risk of this debilitating birth defect. Most studies addressed these genes individually, often with different populations providing conflicting results. OBJECTIVES: Our study evaluates several folate pathway genes for association with human NTDs, incorporating an environmental cofactor: maternal folate supplementation. METHODS: In 304 Caucasian American NTD families with myelomeningocele or anencephaly, we examined 28 polymorphisms in 11 genes: folate receptor 1, folate receptor 2, solute carrier family 19 member 1, transcobalamin II, methylenetetrahydrofolate dehydrogenase 1, serine hydroxymethyl-transferase 1, 5,10-methylenetetrahydrofolate reductase (MTHFR), 5-methyltetrahydrofolate-homo-cysteine methyltransferase, 5-methyltetrahydrofolate-homocysteine methyltransferase reductase, betaine-homocysteine methyltransferase (BHMT), and cystathionine-beta-synthase. RESULTS: Only single nucleotide polymorphisms (SNPs) in BHMT were significantly associated in the overall data set; this significance was strongest when mothers took folate-containing nutritional supplements before conception. The BHMT SNP rs3733890 was more significant when the data were stratified by preferential transmission of the MTHFR rs1801133 thermolabile T allele from parent to offspring. Other SNPs in folate pathway genes were marginally significant in some analyses when stratified by maternal supplementation, MTHFR, or BHMT allele transmission. CONCLUSIONS: BHMT rs3733890 is significantly associated in our data set, whereas MTHFR rs1801133 is not a major risk factor. Further investigation of folate and methionine cycle genes will require extensive SNP genotyping and/or resequencing to identify novel variants, inclusion of environmental factors, and investigation of gene–gene interactions in large data sets

High Density SNP Screen in A Large Multiplex Neural Tube Defect Family Refines Linkage to Loci at 7p21-Pter And 2q33.1-35

Neural tube defects (NTDs) are considered complex with both genetic and environmental factors implicated. To date, no major causative genes have been identified in humans despite several investigations. The first genomewide screen in NTDs (Rampersaud et al. 2005) demonstrated evidence of linkage to chromosomes 7 and 10. This screen included forty-four multiplex families and consisted of 402 microsatellite markers spaced approximately 10 cM apart. Further investigation of the genomic screen data identified a single large multiplex family, pedigree 8776, as primarily driving the linkage results on chromosome 7

High-density single nucleotide polymorphism screen in a large multiplex neural tube defect family refines linkage to loci at 7p21.1-pter and 2q33.1-q35

BACKGROUND: Neural tube defects (NTDs) are considered complex with both genetic and environmental factors implicated. To date, no major causative genes have been identified in humans despite several investigations. The first genomewide screen in NTDs (Rampersaud et al. 2005) demonstrated evidence of linkage to chromosomes 7 and 10. This screen included forty-four multiplex families and consisted of 402 microsatellite markers spaced approximately 10 cM apart. Further investigation of the genomic screen data identified a single large multiplex family, pedigree 8776, as primarily driving the linkage results on chromosome 7. METHODS: To investigate this family more thoroughly, a high-density single nucleotide polymorphism (SNP) screen was performed. Two-point and multipoint linkage analyses were performed using both parametric and nonparametric methods. RESULTS: For both the microsatellite and SNP markers, linkage analysis suggested the involvement of a locus or loci proximal to the telomeric regions of chromosomes 2q and 7p, with both regions having nonparametric lod* scores of ~3.0, yielding very similar evidence in favor of linkage. CONCLUSIONS: The regions of strongest evidence for linkage map proximal to the telomeres on these two chromosomes. In addition to mutations and/or variants in a major gene, these loci may harbor a microdeletion and/or translocation; potentially, polygenic factors may also be involved. This single family may be promising for narrowing the search for NTD susceptibility genes

Refinement of 2q and 7p loci in a large multiplex NTD family

NTDs are considered complex disorders that arise from an interaction between genetic and environmental factors. NTD family 8776 is a large multigenerational Caucasian family that provides a unique resource for the genetic analysis of NTDs. Previous linkage analysis using a genome-wide SNP screen in family 8776 with multipoint nonparametric mapping methods identified maximum LOD* scores of approximately 3.0 mapping to 2q33.1-q35 and 7p21.1-pter. We ascertained an additional nuclear branch of 8776 and conducted additional linkage analysis, fine mapping, and haplotyping. Expression data from lymphoblast cell lines were used to prioritize candidate genes within the minimum candidate intervals. Genomic copy number changes were evaluated using BAC tiling arrays and subtelomeric fluorescent in situ hybridization probes. Increased evidence for linkage was observed with LOD* scores of approximately 3.3 for both regions. Haplotype analyses narrowed the minimum candidate intervals to a 20.3 Mb region in 2q33.1-q35 between markers rs1050347 and D2S434, and an 8.3 Mb region in 7p21.1-21.3 between a novel marker 7M0547 and rs28177. Within these candidate regions, 16 genes were screened for mutations; however, no obvious causative NTD mutation was identified. Evaluation of chromosomal aberrations using comparative genomic hybridization arrays, subtelomeric fluorescent in situ hybridization, and copy number variant detection techniques within the 2q and 7p regions did not detect any chromosomal abnormalities. This large NTD family has identified two genomic regions that may harbor NTD susceptibility genes. Ascertainment of another branch of family 8776 and additional fine mapping permitted a 9.1 Mb reduction of the NTD candidate interval on chromosome 7 and 37.3 Mb on chromosome 2 from previously published data. Identification of one or more NTD susceptibility genes in this family could provide insight into genes that may affect other NTD families

Analysis of ALDH1A2, CYP26A1, CYP26B1, CRABP1, and CRABP2 in human neural tube defects suggests a possible association with alleles in ALDH1A2

BACKGROUND Vitamin A (retinol), in the form of retinoic acid (RA), is essential for normal development of the human embryo. Studies in the mouse and zebrafish have shown that retinol is metabolized in the developing spinal cord and must be maintained in a precise balance along the anteroposterior axis. Both excess and deficiency of RA can affect morphogenesis, including failures of neural tube closure. METHODS We chose to investigate 5 genes involved in the metabolism or synthesis of RA, ALDH1A2, CYP26A1, CYP26B1, CRABP1, and CRABP2, for their role in the development of human neural tube defects, such as spina bifida. RESULTS An association analysis using both allelic and genotypic single‐locus tests revealed a significant association between the risk for spina bifida and 3 polymorphisms in the gene ALDH1A2; however, we found no evidence of a significant multilocus association. CONCLUSIONS These results may suggest that polymorphisms in ALDH1A2 may influence the risk for lumbosacral myelomeningocele in humans. Birth Defects Research (Part A), 2005. © 2005 Wiley‐Liss, Inc