Folate-related gene variants in Irish families affected by neural tube defects.

Fisk Green R, Byrne J, Crider KS, Gallagher M, Koontz D, Berry RJ. (2013) Folate-related gene variants in Irish families affected by neural tube defects. Frontiers in Genetics. 2013 Nov 6;4:223.

 

Periconceptional folic acid use can often prevent neural tube defects (NTDs). Variants of genes involved in folate metabolism in mothers and children have been associated with occurrence of NTDs. We identified Irish families with individuals affected by neural tube defects. In these families, we observed that neural tube defects and birth defects overall occurred at a higher rate in the maternal lineage compared with the paternal lineage. The goal of this study was to look for evidence for genetic effects that could explain the discrepancy in the occurrence of these birth defects in the maternal vs. paternal lineage. We genotyped blood samples from 322 individuals from NTD-affected Irish families, identified through their membership in spina bifida associations. We looked for differences in distribution in maternal vs. paternal lineages of five genetic polymorphisms: the DHFR 19 bp deletion, MTHFD1 1958G>A, MTHFR 1298A>C, MTHFR 677C>T, and SLC19A1 80A>G. In addition to looking at genotypes individually, we determined the number of genotypes associated with decreased folate metabolism in each relative ("risk genotypes") and compared the distribution of these genotypes in maternal vs. paternal relatives. Overall, maternal relatives had a higher number of genotypes associated with lower folate metabolism than paternal relatives (p = 0.017). We expected that relatives would share the same risk genotype as the individuals with NTDs and/or their mothers. However, we observed that maternal relatives had an over-abundance of any risk genotype, rather than one specific genotype. The observed genetic effects suggest an epigenetic mechanism in which decreased folate metabolism results in epigenetic alterations related to the increased rate of NTDs and other birth defects seen in the maternal lineage. Future studies on the etiology of NTDs and other birth defects could benefit from including multigenerational extended families, in order to explore potential epigenetic mechanisms.

 

 

doi: 10.3389/fgene.2013.00223.

 

Free PMC Article

Genetic association analyses of nitric oxide synthase genes and neural tube defects vary by phenotype.

Soldano KL, Garrett ME, Cope HL, Rusnak JM, Ellis NJ, Dunlap KL, Speer MC, Gregory SG, Ashley-Koch AE. (2013) Genetic association analyses of nitric oxide synthase genes and neural tube defects vary by phenotype.  Birth defects research. Part B, Developmental and reproductive toxicology. Oct;98(5):365-73. 

Neural tube defects (NTDs) are caused by improper neural tube closure during the early stages of embryonic development. NTDs are hypothesized to have a complex genetic origin and numerous candidate genes have been proposed. The nitric oxide synthase 3 (NOS3) G594T polymorphism has been implicated in risk for spina bifida, and interactions between that single nucleotide polymorphism (SNP) and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism have also been observed. To evaluate other genetic variation in the NO pathway in the development of NTDs, we examined all three NOS genes: NOS1, NOS2, and NOS3. Using 3109 Caucasian samples in 745 families, we evaluated association in the overall dataset and within specific phenotypic subsets. Haplotype tagging SNPs in the NOS genes were tested for genetic association with NTD subtypes, both for main effects as well as for the presence of interactions with the MTHFR C677T polymorphism. Nominal main effect associations were found with all subtypes, across all three NOS genes, and interactions were observed between SNPs in all three NOS genes and MTHFR C677T. Unlike the previous report, the most significant associations in our dataset were with cranial subtypes and the AG genotype of rs4795067 in NOS2 (p = 0.0014) and the interaction between the rs9658490 G allele in NOS1 and MTHFR 677TT genotype (p = 0.0014). Our data extend the previous findings by implicating a role for all three NOS genes, independently and through interactions with MTHFR, in risk not only for spina bifida, but all NTD subtypes.

doi: 10.1002/bdrb.21079. 

Exon sequencing of PAX3 and T (Brachyury) in cases with spina bifida.

Agopian AJ, Bhalla AD, Boerwinkle E, Finnell RH, Grove ML, Hixson JE, Shimmin LC, Sewda A, Stuart C, Zhong Y, Zhu H, Mitchell LE. (2013) Exon sequencing of PAX3 and T (Brachyury) in cases with spina bifida. Birth Defects Res A Clin Mol Teratol. 2013 Aug 2.

Human Genetics Center, Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, Texas.

Abstract

BACKGROUND:
Based on studies in animals and humans, PAX3 and T (brachyury) are candidate genes for spina bifida. However, neither gene has been definitively identified as a risk factor for this condition.

METHODS:
Sanger sequencing was used to identify variants in all PAX3 and T exons and promoter regions in 114 spina bifida cases. For known variants, allele frequencies in cases were compared with those from public databases using unadjusted odds ratios. Novel variants were genotyped in parents and assessed for predicted functional impact.

RESULTS:
We identified common variants in PAX3 (n = 2) and T (n = 3) for which the allele frequencies in cases were significantly different from those reported in at least one public database. We also identified novel variants in both PAX3 (n = 11) and T (n = 1) in spina bifida cases. Several of the novel PAX3 variants are predicted to be highly conserved and/or impact gene function or expression.

CONCLUSION:
These studies provide some evidence that common variants of PAX3 and T are associated with spina bifida. Rare and novel variants in these genes were also identified in affected individuals. However, additional studies will be required to determine whether these variants influence the risk of spina bifida. Birth Defects Research (Part A), 2013. © 2013 Wiley Periodicals, Inc.

PAX3, T locus, genetic epidemiology, myelomeningocele, sequencing, spina bifida, word

PMID: 23913553

Mutations in Planar Cell Polarity Gene SCRIB Are Associated with Spina Bifida.

Lei Y, Zhu H, Duhon C, Yang W, Ross ME, Shaw GM, Finnell RH. (2013) Mutations in Planar Cell Polarity Gene SCRIB Are Associated with Spina Bifida. PLoS One. 2013 Jul 26;8(7):e69262.

Dell Pediatric Research Institute, Department of Nutritional Sciences, the University of Texas at Austin, Austin, Texas, United States of America.

Abstract

Neural tube defects (NTDs) (OMIM #182940) including anencephaly, spina bifida and craniorachischisis, are severe congenital malformations that affect 0.5-1 in 1,000 live births in the United States, with varying prevalence around the world. Mutations in planar cell polarity (PCP) genes are believed to cause a variety of NTDs in both mice and humans. SCRIB is a PCP-associated gene. Mice that are homozygous for the Scrib p.I285K and circletail (Crc) mutations, present with the most severe form of NTDs, namely craniorachischisis. A recent study reported that mutations in SCRIB were associated with craniorachischisis in humans, but whether SCRIB mutations contribute to increased spina bifida risk is still unknown. We sequenced the SCRIB gene in 192 infants with spina bifida and 190 healthy controls. Among the spina bifida patients, we identified five novel missense mutations that were predicted-to-be-deleterious by the PolyPhen software. Of these five mutations, three of them (p.P1043L, p.P1332L, p.L1520R) significantly affected the subcellular localization of SCRIB. In addition, we demonstrated that the craniorachischisis mouse line-90 mutation I285K, also affected SCRIB subcellular localization. In contrast, only one novel missense mutation (p.A1257T) was detected in control samples, and it was predicted to be benign. This study demonstrated that rare deleterious mutations of SCRIB may contribute to the multifactorial risk for human spina bifida.

PMID: 23922697

A genetic signature of spina bifida risk from pathway-informed comprehensive gene-variant analysis.

Marini NJ, Hoffmann TJ, Lammer EJ, Hardin J, Lazaruk K, Stein JB, Gilbert DA, Wright C, Lipzen A, Pennacchio LA, Carmichael SL, Witte JS, Shaw GM, Rine J. (2011) A genetic signature of spina bifida risk from pathway-informed comprehensive gene-variant analysis. PLoS One. 2011;6(11):e28408.

Despite compelling epidemiological evidence that folic acid supplements reduce the frequency of neural tube defects (NTDs) in newborns, common variant association studies with folate metabolism genes have failed to explain the majority of NTD risk. The contribution of rare alleles as well as genetic interactions within the folate pathway have not been extensively studied in the context of NTDs. Thus, we sequenced the exons in 31 folate-related genes in a 480-member NTD case-control population to identify the full spectrum of allelic variation and determine whether rare alleles or obvious genetic interactions within this pathway affect NTD risk. We constructed a pathway model, predetermined independent of the data, which grouped genes into coherent sets reflecting the distinct metabolic compartments in the folate/one-carbon pathway (purine synthesis, pyrimidine synthesis, and homocysteine recycling to methionine). By integrating multiple variants based on these groupings, we uncovered two provocative, complex genetic risk signatures. Interestingly, these signatures differed by race/ethnicity: a Hispanic risk profile pointed to alterations in purine biosynthesis, whereas that in non-Hispanic whites implicated homocysteine metabolism. In contrast, parallel analyses that focused on individual alleles, or individual genes, as the units by which to assign risk revealed no compelling associations. These results suggest that the ability to layer pathway relationships onto clinical variant data can be uniquely informative for identifying genetic risk as well as for generating mechanistic hypotheses. Furthermore, the identification of ethnic-specific risk signatures for spina bifida resonated with epidemiological data suggesting that the underlying pathogenesis may differ between Hispanic and non-Hispanic groups.

PMID: 22140583

Genetic association study of putative functional single nucleotide polymorphisms of genes in folate metabolism and spina bifida.

Martinez CA, Northrup H, Lin JI, Morrison AC, Fletcher JM, Tyerman GH, Au KS. (2009) Genetic association study of putative functional single nucleotide polymorphisms of genes in folate metabolism and spina bifida. American Journal of Obstetrics and Gynecology. 2009 Aug 14.

Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Texas Health Science Center at Houston, Houston, TX.

OBJECTIVE: We tested putative functional single nucleotide polymorphisms (SNPs) in genes that regulate the folate/homocysteine metabolism pathway for their contribution to spina bifida (SB) susceptibility.

STUDY DESIGN: The study consisted of 610 unrelated simplex SB patient families. Genotypes of 46 SNPs located in the coding sequence or promoter region of 11 genes were investigated. Associations between transmission of alleles and SB in the offspring were examined using the reconstruction combined transmission disequilibrium test.

RESULTS: Significant association of SNP rs5742905 in cystathionine-beta-synthase, rs1643649 in dihydrofolate reductase, rs2853533 in thymidylate synthetase, and rs3737965 in methylenetetrahydrofolate reductase was found (P = .015, .041, .021, and .007 respectively).

CONCLUSION: Transmission disequilibrium of SNP alleles in cystathionine-beta-synthase, dihydrofolate reductase, methylenetetrahydrofolate reductase, and thymidylate synthetase confers an increased susceptibility to SB.

PMID: 19683694

Evaluation of the levels of folate, vitamin B12, homocysteine and fluoride in the parents and the affected neonates with neural tube defect and their

Ratan SK, Rattan KN, Pandey RM, Singhal S, Kharab S, Bala M, Singh V, Jhanwar A. (2008) Evaluation of the levels of folate, vitamin B12, homocysteine and fluoride in the parents and the affected neonates with neural tube defect and their matched controls. Pediatric Surgery International. Jul;24(7):803-8.

Department of Pediatric Surgery, Pandit BD Sharma Post Graduate Institute of Medical Sciences, Rohtak, Haryana, India. drjohnsimmi@yahoo.com

The aim of this study is to evaluate the folate, vitamin B12, fluoride and homocysteine levels in newborns with neural tube defect (NTD) and their parents. The study included 35 neonates with NTD and their parents, 31 neonates with congenital anomalies other than NTD formed control 1, 24 neonates with no anomalies, with the highest birth order and normal siblings formed control 2. These groups matched for socio-economic and nutritional status. Demographic, antenatal history, parental habits, folate (RBC, whole blood and serum), serum vitamin B12 and homocysteine levels were estimated using chemiluminescence technology. Chi-square test was used to assess association between factors and the outcome. One-way ANOVA was used to compare means in the three groups. To determine the risk factors for NTD, odds ratios (95% CI) was computed using bivariate and multivariate logistic regression analysis (STATA 9.0). No difference was found between NTD group and 'control 1' group. The fathers in NTD group had significantly lower folate and vitamin B12 and a higher homocysteine, in comparison to 'control 2' group (i.e. with normal babies). The babies with NTD had higher homocysteine while their mothers had significantly low folate levels in comparison to 'control 2' mothers. Low RBC folate, low serum vitamin B12 and high plasma homocysteine in both the parents had an association with NTD. Multivariate logistic regression revealed high homocysteine of father as the only independent significant risk factor [OR(95% CI):2.6(2.6, 226)] for NTD and also for other anomalies. NTD (and other congenital anomalies) may not only be due to nutritional deficiency in the mothers but also due to more intricate gene-nutrient interaction defects in the affected families, probably some abnormal folate-homocysteine metabolism. These defects seem to be affect the fathers more severely and in all likelihood, get transmitted to the babies from either or both the parents. The emergence of father's serum homocysteine levels as an independent risk factor for NTD and also other congenital anomalies calls for further studies to evaluate if this can be taken as a marker for congenital anomalies in the fetus during antenatal screening.

PMID: 18463884

Epidemiology of neural tube defects.

Frey L, Hauser WA. Epidemiology of neural tube defects. Epilepsia. 2003;44 Suppl 3:4-13. Review.

Department of Neurology, G. H. Sergievsky Center, College of Physicians & Surgeons, Columbia University, New York, New York 10032, USA.

Neural tube defects (NTDs)-malformations secondary to abnormal neural tube closure between the third and fourth weeks of gestational age-have a complex and imperfectly understood etiology in which both genetic and environmental factors appear to be involved. A number of specific chromosomal or single-gene disorders, presumably not affected by environmental influences, are associated with the development of NTDs, but such syndromal cases account for a small proportion of NTDs in live-born infants. Analysis of recurrence patterns within families and of twin-concordance data provides evidence of a genetic influence in nonsyndromal cases, but factors such as socioeconomic status and geographic area (independent of race or ethnicity) are also associated with variations in the incidence of NTDs. The prevalence at birth of both anencephaly and spina bifida has decreased, but the advent of antenatal diagnosis and elective termination of affected pregnancies has undermined the reliability of birth prevalence rate as an estimate of incidence. Some occupational and other exposures, including maternal use of antiepileptic drugs (AEDs), are associated with increased risk for NTDs. Among women who have had an NTD-affected pregnancy, recurrence risk is markedly higher than the risk for a first NTD-affected pregnancy in the general population. There is strong evidence, overall, for a protective effect of adequate folate consumption. In some high-risk groups, however, such as women taking AEDs, folate supplementation has not been proven to reduce NTD risk.

PMID: 12790881

Adverse reproductive outcomes among pregnancies of aunts and (spouses of) uncles in Irish families with neural tube defects

Byrne J, Carolan S. Adverse reproductive outcomes among pregnancies of aunts and (spouses of) uncles in Irish families with neural tube defects. American journal of medical genetics. Part A. 2006 Jan 1;140(1):52-61.

Boyne Research Institute, 5 Potato Market Square East, Drogheda, Ireland. boyne.research@verizon.net

Adverse pregnancy outcomes may be more frequent among sibs of individuals with neural tube defects (NTDs), and transmission of risk in families with an NTD may be more frequent among maternal relatives. In a study designed to evaluate matrilineal risk for NTDs, we compared adverse pregnancy outcomes among maternal and paternal first cousin pregnancies. Pregnancy histories were obtained by interview with 288 uncles and aunts (parents of the first cousin pregnancies) in 48 Irish NTD families. We analyzed pregnancy outcomes (preterm deliveries, stillbirths, and miscarriages) among 1,033 singleton first cousin pregnancies and compared risk among maternal versus paternal relatives. Maternal first cousin pregnancies were more likely to end adversely when compared to paternal first cousin pregnancies (17.4% vs. 11.7%, P = 0.01). In a logistic regression analysis of pregnancies unaffected by birth defects, maternal line remained independently associated with adverse outcomes (odds ratio (OR) = 1.55, 95% confidence interval (CI) 1.06, 2.27) after controlling for NTD type, maternal age, maternal smoking during pregnancy, first cousin pregnancy's year of birth. The excess risk with maternal line related mainly to spina bifida occulta families (OR = 42.4; CI 2.64, 681; P = 0.008); risk in open spina bifida families was 1.24 (CI 0.82, 1.87; P = 0.3). These results support the hypothesis of excess risk for adverse pregnancy outcomes among maternal relatives in NTD families. Further work is needed, epidemiological as well as clinical and molecular, not only to confirm these findings, but also to define the underlying biological mechanisms linking adverse reproductive outcomes, excess maternal risk and occurrence of NTDs.

PMID: 16333827

Further evidence for a maternal genetic effect and a sex-influenced effect contributing to risk for human neural tube defects.

Deak KL, Siegel DG, George TM, Gregory S, Ashley-Koch A, Speer MC; NTD Collaborative Group. (2008) Further evidence for a maternal genetic effect and a sex-influenced effect contributing to risk for human neural tube defects. Birth defects research. Part A, Clinical and molecular teratology. 2008 Oct;82(10):662-9.

Center for Human Genetics, Duke University Medical Center, Durham, North Carolina, USA.

BACKGROUND: Neural tube defects (NTDs), including spina bifida and anencephaly, are the second most common birth defect with an incidence of 1/1000. Genetic factors are believed to contribute to NTD risk and family-based studies can be useful for identifying such risk factors.

METHODS: We ascertained 1066 NTD families (1467 affected patients), including 307 multiplex NTD families. We performed pedigree analysis to describe the inheritance patterns, pregnancy outcomes, and recurrence risks to relatives of various types.

RESULTS: Myelomeningocele or spina bifida (66.9%) and cranial defects (17.7%) were the most common NTD subtypes observed. The overall male:female ratio for affected individuals was 0.82, and there were even fewer males among individuals with an upper level NTD (0.62). Among twins, 2 of the 5 monozygotic twins and only 3 of 35 dizygotic twins were concordant, while 27% of the same sex twins were concordant, but none of the different sex twins. The estimated 6.3% recurrence risk to siblings (CI 0.04-0.08) is consistent with previous reports. Families with two or more affected individuals show a higher proportion of female transmitters (p = 0.0002). Additionally, the number of affected relatives in maternal compared to paternal lineages was more than double (p = 0.006). There were significantly more miscarriages, infant deaths, and stillborn pregnancies of the maternal aunts and uncles (p < 0.0001) and of first cousins (p = 0.04).

CONCLUSIONS: Our data provide several lines of evidence consistent with a maternal effect, as well as a sex-influenced effect, in the etiology of NTDs.

PMID: 18937341

Interaction of PDGFRA promoter haplotypes and maternal environmental exposures in the risk of spina bifida

Toepoel M, Steegers-Theunissen RP, Ouborg NJ, Franke B, Ladd AM, Joosten PH, van Zoelen EJ. (2009) Interaction of PDGFRA promoter haplotypes and maternal environmental exposures in the risk of spina bifida. Birth Defects Research A: Clinical and Molecular Teratology. 2009 Feb 12.

Department of Cell Biology, Faculty of Science, Radboud University Nijmegen, Nijmegen, the Netherlands.

BACKGROUND: Neural tube defects are multifactorial malformations involving both environmental exposures, such as maternal nutrition, and genetic factors. Aberrant expression of the platelet-derived growth factor alpha-receptor (PDGFRA) gene has been implicated in neural-tube-defect etiology in both mice and humans.

METHODS: We investigated possible interactions between the PDGFRA promoter haplotype of mother and child, as well as maternal glucose, myo-inositol, and zinc levels, in relation to spina bifida offspring. Distributions were determined of the PDGFRA promoter haplotypes H1 and H2 in a Dutch cohort, consisting of 88 spina bifida children with 56 of their mothers, and 74 control children with 72 of their mothers, as well as maternal plasma glucose, myo-inositol, and red blood cell zinc concentrations.

RESULTS: A significantly higher frequency of H1 was observed in children with spina bifida than in controls (30.1 vs. 20.3%; OR = 1.69, 95% CI 1.02-2.83). High maternal body mass index (BMI) and glucose were significant risk factors for both H1 and H2 children, whereas low myo-inositol and zinc were risk factors for H2 but not for H1 children. Stepwise multiple logistic regression analysis showed that high maternal glucose and low myo-inositol are the main risk factors for H2 spina bifida children, whereas for H1 spina bifida children, maternal BMI was the main risk factor. Interestingly, H1 mothers (median 165.5 cm) showed a significantly lower body height than H2 mothers (median 169.1 cm; p = 0.003).

CONCLUSIONS: These data suggest that the child's PDGFRA promoter haplotype is differentially sensitive for periconceptional exposure to glucose, myo-inositol, and zinc in the risk of spina bifida. Birth Defects Research (Part A), 2009. (c) 2009 Wiley-Liss, Inc.

PMID: 19215021

Mouse hitchhiker mutants have spina bifida, dorso-ventral patterning defects and polydactyly: Identification of Tulp3 as a novel negative regulator of

Patterson VL, Damrau C, Paudyal A, Reeve B, Grimes DT, Stewart ME, Williams DJ, Siggers P, Greenfield A, Murdoch JN. (2009) Mouse hitchhiker mutants have spina bifida, dorso-ventral patterning defects and polydactyly: Identification of Tulp3 as a novel negative regulator of the Sonic hedgehog pathway. Human Molecular Genetics. 2009 Feb 17.

Mammalian Genetics Unit.

The mammalian sonic hedgehog (Shh) signalling pathway is essential for embryonic development and the patterning of multiple organs. Disruption or activation of Shh signalling leads to multiple birth defects, including holoprosencephaly, neural tube defects and polydactyly, and in adults results in tumours of the skin or central nervous system. Genetic approaches with model organisms continue to identify novel components of the pathway, including key molecules that function as positive or negative regulators of Shh signalling. Data presented here define Tulp3 as a novel negative regulator of the Shh pathway. We have identified a new mouse mutant that is a strongly hypomorphic allele of Tulp3 and which exhibits expansion of ventral markers in the caudal spinal cord, as well as neural tube defects and preaxial polydactyly, consistent with increased Shh signalling. We demonstrate that Tulp3 acts genetically downstream of Shh and Smoothened (Smo) in neural tube patterning and exhibits a genetic interaction with Gli3 in limb development. We show that Tulp3 does not appear to alter expression or processing of Gli3, and we demonstrate that transcriptional regulation of other negative regulators (Rab23, Fkbp8, Thm1, Sufu and PKA) is not affected. We discuss the possible mechanism of action of Tulp3 in Shh-mediated signalling in light of these new data.

PMID: 19223390

Mini-review: toward understanding mechanisms of genetic neural tube defects in mice

Harris MJ, Juriloff DM. Mini-review: toward understanding mechanisms of genetic neural tube defects in mice. Teratology. 1999 Nov;60(5):292-305. Review.

We review the data from studies of mouse mutants that lend insight to the mechanisms that lead to neural tube defects (NTDs). Most of the 50 single-gene mutations that cause neural tube defects (NTDs) in mice also cause severe embryonic-lethal syndromes, in which exencephaly is a nonspecific feature. In a few mutants (e.g., Trp53, Macs, Mlp or Sp), other defects may be present, but affected fetuses can survive to birth. Multifactorial genetic causes, as are present in the curly tail stock (15-20% spina bifida), or the SELH/Bc strain (15-20% exencephaly), lead to nonsyndromic NTDs. The mutations indicate that "spina bifida occulta," a dorsal gap in the vertebral arches over an intact neural tube, is usually genetically and developmentally unrelated to exencephaly or "spina bifida" (aperta). Almost all exencephaly or spina bifida aperta of genetic origin is caused by failure of neural fold elevation. The developmental mechanisms in genetic NTDs are considered in terms of distinct rostro-caudal zones along the neural folds that likely differ in mechanism of elevation. Failure of elevation leads to: split face (zone A), exencephaly (zone B), rachischisis (all of zone D), or spina bifida (caudal zone D). The developmental mechanisms leading to these genetic NTDs are heterogeneous, even within one zone. At the tissue level, the mutants show that the mechanism of failure of elevation can involve, e.g., (1) slow growth of adjacent tethered tissue (curly tail), (2) defective forebrain mesenchyme (Cart1 or twist), (3) defective basal lamina in surface ectoderm (Lama5), (4) excessive breadth of floorplate and notochord (Lp), (5) abnormal neuroepithelium (Apob, Sp, Tcfap2a), (6) morphological deformation of neural folds (jmj), (7) abnormal neuroepithelial and neural crest cell gap-junction communication (Gja1), or (8) incomplete compensation for a defective step in the elevation sequence (SELH/Bc). At the biochemical level, mutants suggest involvement of: (1) faulty regulation of apoptosis (Trp53 or p300), (2) premature differentiation (Hes1), (3) disruption of actin function (Macs or Mlp), (4) abnormal telomerase complex (Terc), or (5) faulty pyrimidine synthesis (Sp). The NTD preventative effect of maternal dietary supplementation is also heterogeneous, as demonstrated by: (1) methionine (Axd), (2) folic acid or thymidine (Sp), or (3) inositol (curly tail). The heterogeneity of mechanism of mouse NTDs suggests that human NTDs, including the common nonsyndromic anencephaly or spina bifida, may also reflect a variety of genetically caused defects in developmental mechanisms normally responsible for elevation of the neural folds.

PMID: 10525207

Birth defects in uncles and aunts from Irish families with neural tube defects

Byrne J. Birth defects in uncles and aunts from Irish families with neural tube defects. Birth Defects Reseach, Part A: Clinical Molecular Teratology. 2007 Nov 28;

BACKGROUND:: Previous studies suggested an excess of matrilineal cases of neural tube defects among distant relatives in NTD families. There is little information on patterns of heredity of other birth defects among distant relatives.

METHODS:: Between 1995 and 2003, 78 nuclear families and 373 uncles and aunts were interviewed about birth defects among uncles and aunts in Irish families with an NTD.

RESULTS:: Among 783 total uncles and aunts, those related through the mother had more birth defects overall than those related through the father (8.4 vs. 4.0%, p = 0.01). The excess persisted after controlling with logistic regression models for maternal and paternal age, gender of uncle/aunt, proband's NTD diagnosis, and year of birth (OR 2.52; 95% CI: 1.29, 4.91; p = 0.007). Among individual birth defects, significant excesses over expected rates were seen for spina bifida, congenital heart defects, and syndactyly.

CONCLUSIONS:: This study of reported birth defects suggests that maternal uncles and aunts in Irish families have significantly more birth defects than paternal uncles and aunts. These results, if confirmed, support the hypothesis that NTD relatives carry a susceptibility to other birth defects, preferentially on the mother's side of the family, suggesting opportunities for prevention. Birth Defects Research (Part A) 2007.

PMID: 18044714

Homocysteine, folate, lipid profile and MTHFR genotype and disability in children with myelomeningocele

Rendeli C, Ausili E, Castorina M, Antuzzi D, Tabacco F, Caldarelli M. Homocysteine, folate, lipid profile and MTHFR genotype and disability in children with myelomeningocele. Child's Nervous System. 2006 Oct;22(10):1316-21. Epub 2006 Apr 7.

STUDY DESIGN: We performed a cross-sectional study in myelomeningocele children. OBJECTIVE: To investigate plasma total homocysteine, folate, lipid profile, 5,10- metylenetetrahydrofolate reductase genotype (MTHFR) and disability.

MATERIALS AND METHODS: Sixty patients aged between 2 and 14 years with myelomeningocele (18 ambulatory and 42 non-ambulatory) and 150 healthy children of same age, are investigated for lipid profile, homocysteine concentration and for the determination of MTHFR genotype.

RESULTS: Plasma homocysteine concentrations were significantly higher in myelomeningocele children than in the control group. In myelomeningocele female group, there were higher levels of total cholesterol and very-low-density lipoprotein cholesterol with respect to the control group. Myelomeningocele children walking with tutorial aid showed triglyceride levels significantly lower than those observed in myelomeningocele non-walking children.

CONCLUSION: Disability, insulin uptake, lipid, homocysteine, hormones plasma levels, and genetic factors such as allelic variants of MTHFR are possible for cardiovascular disease in myelomeningocele children. This study highlights the importance of a continuous surveillance of any changes in the lipid profile that should be corrected as soon as possible. Constant physical activity necessary to increase HDL levels should be planned in all susceptible children. Nonetheless, further investigations are necessary to identify new homocysteine susceptible genes for prevention of early atherosclerosis and consequent cardiovascular disease.

PMID: 16602021

Myelomeningocele: a review of the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals

Shaer CM, Chescheir N, Schulkin J. Myelomeningocele: a review of the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals. Obstetrical & Gynecological Survey. 2007 Jul;62(7):471-9. Review.

Although the use of folic acid before conception decreases the chance that a fetus will have an open neural tube defect, this condition still affects 0.5-1.0/1000 pregnancies in the United States. Results of a recent survey suggest that there are gaps in obstetrician-gynecologists' knowledge of risk factors for conception, strategies for prenatal diagnosis, and prognosis for affected individuals. To address these gaps this paper reviews the epidemiology, genetics, risk factors for conception, prenatal diagnosis, and prognosis for affected individuals, presents current information, and makes suggestions for expanding obstetrician-gynecologists' knowledge of myelomeningocele.

TARGET AUDIENCE: Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES: After completion of this article, the reader should be able to state that despite a large amount of professional and public education on the use of folic acid in prevention of open neural tube defects (ONTDs) the incidence still affects 0.5-1.0/1000 pregnancies and recall that a recent survey conducted by the ACOG shows substantial misunderstanding and misinformation on major categories of neural tube birth defects.

PMID: 17572919

Identification of minimal enhancer elements sufficient for Pax3 expression in neural crest and implication of Tead2 as a regulator of Pax3

Milewski RC, Chi NC, Li J, Brown C, Lu MM, Epstein JA. Identification of minimal enhancer elements sufficient for Pax3 expression in neural crest and implication of Tead2 as a regulator of Pax3. Development. 2004 Feb;131(4):829-37. Epub 2004 Jan 21.

Pax3 is a transcription factor that is required by pre-migratory neural crest cells, which give rise to the peripheral nervous system, melanocytes, some vascular smooth muscle, and numerous other derivatives [corrected]. Both mice and humans with Pax3 deficiency exhibit neural crest-related developmental defects [corrected]. Pax3 is also expressed in the dorsal neural tube, and by myogenic progenitors in the presomitic mesoderm and the hypaxial somites. Molecular pathways that regulate Pax3 expression in the roof plate probably represent early upstream signals in neural crest induction. We have identified an enhancer region in the Pax3 genomic locus that is sufficient to recapitulate expression in neural crest precursors in transgenic mice. We show that Tead2, a member of the Tead box family of transcription factors, binds to a neural crest enhancer and activates Pax3 expression. Tead2, and its co-activator YAP65, are co-expressed with Pax3 in the dorsal neural tube, and mutation of the Tead2 binding site in the context of Pax3 transgenic constructs abolishes neural expression. In addition, a Tead2-Engrailed fusion protein is able to repress retinoic acid-induced Pax3 expression in P19 cells and in vivo. These results suggest that Tead2 is an endogenous activator of Pax3 in neural crest.

PMID: 14736747

Transcription factor TEAD2 is involved in neural tube closure.

Kaneko KJ, Kohn MJ, Liu C, Depamphilis ML. Transcription factor TEAD2 is involved in neural tube closure. Genesis. 2007 Sep;45(9):577-87.

TEAD2, one of the first transcription factors expressed at the beginning of mammalian development, appears to be required during neural development. For example, Tead2 expression is greatest in the dorsal neural crest where it appears to regulate expression of Pax3, a gene essential for brain development. Consistent with this hypothesis, we found that inactivation of the Tead2 gene in mice significantly increased the risk of exencephaly (a defect in neural tube closure). However, none of the embryos exhibited spina bifida, the major phenotype of Pax3 nullizygous embryos, and expression of Pax3 in E11.5 Tead2 nullizygous embryos was normal. Thus, Tead2 plays a role in neural tube closure that is independent of its putative role in Pax3 regulation. In addition, the risk of exencephaly was greatest with Tead2 nullizygous females, and could be suppressed either by folic acid or pifithrin-alpha. These results reveal a maternal genetic contribution to neural tube closure, and suggest that Tead2-deficient mice provide a model for anencephaly, a common human birth defect that can be prevented by folic acid. genesis 45:577-587, 2007. Published 2007 Wiley-Liss, Inc.

PMID: 17868131

Neural plate morphogenesis during mouse neurulation is regulated by antagonism of Bmp signalling

Ybot-Gonzalez P, Gaston-Massuet C, Girdler G, Klingensmith J, Arkell R, Greene ND, Copp AJ. Neural plate morphogenesis during mouse neurulation is regulated by antagonism of Bmp signalling. Development. 2007 Sep;134(17):3203-11.

Dorsolateral bending of the neural plate, an undifferentiated pseudostratified epithelium, is essential for neural tube closure in the mouse spinal region. If dorsolateral bending fails, spina bifida results. In the present study, we investigated the molecular signals that regulate the formation of dorsolateral hinge points (DLHPs). We show that Bmp2 expression correlates with upper spinal neurulation (in which DLHPs are absent); that Bmp2-null embryos exhibit premature, exaggerated DLHPs; and that the local release of Bmp2 inhibits neural fold bending. Therefore, Bmp signalling is necessary and sufficient to inhibit DLHPs. By contrast, the Bmp antagonist noggin is expressed dorsally in neural folds containing DLHPs, noggin-null embryos show markedly reduced dorsolateral bending and local release of noggin stimulates bending. Hence, Bmp antagonism is both necessary and sufficient to induce dorsolateral bending. The local release of Shh suppresses dorsal noggin expression, explaining the absence of DLHPs at high spinal levels, where notochordal expression of Shh is strong. DLHPs ;break through' at low spinal levels, where Shh expression is weaker. Zic2 mutant embryos fail to express Bmp antagonists dorsally and lack DLHPs, developing severe spina bifida. Our findings reveal a molecular mechanism based on antagonism of Bmp signalling that underlies the regulation of DLHP formation during mouse spinal neural tube closure.

PMID: 17693602

Risk of recurrence in major central nervous system malformations between 1976 and 2005

Joo JG, Beke A, Papp Z, Csaba A, Rab A, Papp C. Risk of recurrence in major central nervous system malformations between 1976 and 2005. Prenatal Diagnosis. 2007 Aug 13; [Epub ahead of print]

OBJECTIVE: The goal of the current publication is to review isolated central nervous system malformations (CSMs) using a database in excess of 75 000 cases, with special regard to the risk of recurrence of these malformations alone or in combination.

METHODS: In the period between 1 January 1976 and 31 December 2005, among the 75 320 documented cases, consultations were requested due to earlier isolated CSMs in the patients' histories in 3030 cases (4.2%). Processing the data we only considered disorders of genetic origin, and that was why we excluded the cases due to intrauterine infection. Monogenically inherited malformations were also excluded from the analysis. The diagnosis of the malformations was based on the prenatal diagnosis of ultrasonography as well as the findings of the foetopathological examination.

RESULTS: In 65% of the cases, the couples sought counselling because of malformation in a previous pregnancy. In these cases, the risk of recurrence was thought to be 5.2%, while in the case of two affected children this figure stood at 21.9%. Analysing the values for the risk of recurrence in 5-year periods, neural tube defects (NTDs) (particularly anencephaly and spina bifida) showed a detectable decrease, which could be attributed to a growing use of folic acid supplementation around the time of conception and during pregnancy.

CONCLUSION: There is a clear decrease of risk of recurrence of NTDs, while in the case of the other CSMs in this study, there is no noteworthy chronological change in their risk of recurrence. Copyright (c) 2007 John Wiley & Sons, Ltd.

PMID: 17694579