Risk Of Spina Bifida Research Articles

The methylenetetrahydrofolate dehydrogenase (MTHFD1) 1958G>A variant is not associated with spina bifida risk in the Dutch population

The methylenetetrahydrofolate dehydrogenase (MTHFD1) 1958G>A variant is not associated with spina bifida risk in the Dutch population

Congenital defects among liveborn infants with Down syndrome

Many infants with Down syndrome (DS) have co-occurring congenital malformations requiring intensive surgical and medical management. To anticipate the care needed by these infants, providers and parents require accurate information about birth defects that may be present. This article uses a unique national hospital discharge dataset to identify the rate at which structural birth defects are identified among liveborn infants with DS. ICD-9-CM diagnosis codes for data from the Healthcare Cost and Utilization Project were used to identify infants with and without DS, and to classify birth defects. The study population consisted of liveborn infants discharged from the hospital from 1993 through 2002. ORs for the association between the occurrence of congenital malformations and the presence of DS were computed using logistic regression models for survey data. Discharge data included 11,372 DS and 7,884,209 non-DS births, representing national estimates of 43,463 DS and 39,716,469 non-DS births respectively. In addition to congenital heart defects that co-occurred most often in DS infants compared to infants without DS, the risks for gastrointestinal malformations (OR 67.07), genitourinary malformations (OR 3.62), orofacial malformations (OR 5.63), and abdominal wall malformations (OR 3.25) were also elevated in infants with DS. There was no difference in the risk of spina bifida between infants with and without DS. This is the first nationally representative compilation of the co-occurrence of congenital malformations associated with DS. This information may assist providers and parents in their attempts to understand and prepare for the true burden of this condition.

The 19‐bp deletion polymorphism in intron‐1 of dihydrofolate reductase (DHFR) may decrease rather than increase risk for spina bifida in the Irish population

Periconceptional maternal folic acid supplementation can prevent up to 70% of pregnancies affected with neural tube defects (NTDs), including spina bifida. This has focused attention on folate-related genes such as dihydrofolate reductase (DHFR) in a bid to identify the genetic factors that influence NTD risk through either the fetal or maternal genotype. We considered a novel intronic 19-bp deletion polymorphism and two polymorphisms within the 3' untranslated region (721A>T and 829C>T) of the DHFR gene as candidates for NTD risk. We studied NTD cases (n=283), mothers of cases (n=280), fathers of cases (n=279), and controls (n=256). We did not find the DHFR 829C>T polymorphism to be variable within the Irish population. The 19-bp intron deletion and the 721A>T polymorphisms were found to be in linkage disequilibrium. In contrast to a previous study, the 19-bp intron deletion allele did show a significant protective effect in mothers of NTD cases when present in one (relative risk 0.59 [95%CI: 0.39-0.89], P=0.01) or two copies (relative risk 0.52 [95%CI: 0.32-0.86], P=0.01). Analysis of mRNA levels revealed a small increase in expression ( approximately 1.5-fold) associated with the 19-bp intron deletion polymorphism, but this was not significant. In conclusion, the DHFR intron 19-bp deletion allele may be a protective NTD genetic factor by increasing DHFR mRNA levels in pregnant women.

The 894G>T variant in the endothelial nitric oxide synthase gene and spina bifida risk

The 894G>T single nucleotide polymorphism (SNP) in the endothelial NOS (NOS3) gene, has recently been associated with embryonic spina bifida risk. In this study, a possible association between the NOS3 894G>T SNP and spina bifida risk in both mothers and children in a Dutch population was examined using both a case-control design and a transmission disequilibrium test (TDT). Possible interactions between the NOS3 894G>T SNP and the MTHFR 677C>T SNP, elevated plasma homocysteine, and decreased plasma folate concentrations were also studied. The NOS3 894TT genotype did not increase spina bifida risk in mothers or children (OR 1.50, 95%CI 0.71–3.19 and OR 1.78, 95%CI 0.75–4.25, respectively). The TDT demonstrated no preferential transmission of the NOS3 894T allele (Χ2 = 0.06, P = 0.81). In combination with the MTHFR 677TT genotype or elevated plasma homocysteine concentrations, the NOS3 894GT/TT genotype increased maternal spina bifida risk (OR 4.52, 95%CI 1.55–13.22 and OR 3.38, 95%CI 1.46–7.84, respectively). In our study population, the NOS3 894GT/TT genotype might be a risk factor for having a spina bifida affected child in mothers who already have an impaired homocysteine metabolism.

Maternal Stressful Life Events and Risks of Birth Defects

Several previous studies suggest that maternal stress may be associated with increased risk of certain birth defects. This study examined the association of maternal stressful life events with risks of several birth defects. The data are from a recent, population-based case-control study. Telephone interviews were conducted with 1355 eligible case mothers and 700 control mothers. Maternal stress was measured by responses to 18 yes/no questions about life events that occurred from 2 months before through 2 months after conception. An increase in the stressful life events index (ie, number of "yes" responses to the 18 life-events questions) was associated with increased risk of cleft palate, cleft lip with or without cleft palate, d-transposition of the great arteries, and tetralogy of Fallot, after adjustment for maternal race-ethnicity, education, obesity, age, smoking, drinking, intake of folic acid-containing supplements, neighborhood crime, and food insecurity. For example, the odds ratio for a 3-unit change in the stress index was 1.45 (95% confidence interval = 1.03-2.06) for cleft palate. Increased stress was associated with an increased risk of spina bifida and anencephaly particularly among women who did not take folic acid supplements. A 3-unit change in stress was associated with a 2.35-fold increased risk of anencephaly among women who did not take supplements (CI =1.47-3.77) and a 1.42-fold increased risk among women who did (CI = 0.89-2.25). The adverse health effects of stress may include increased risks of certain birth defects.

Cost-effectiveness of a folic acid fortification program in Chile

Objective Periconceptional intake of folic acid reduces the risk of neural tube defects (NTDs), a frequent birth defect that can cause significant infant mortality and disability. In Chile, fortification of wheat flour with folic acid has resulted in significant reduction in the risk of anencephaly and spina bifida. We investigated the cost-effectiveness implications of this policy. Methods We conducted an ex-post economic analysis of this intervention. Estimates of the effect of fortification in decreasing NTDs and deaths were derived from a prospective evaluation. The costs of fortification and provision of medical care to children with spina bifida in Chile were based on primary data collection. Findings The intervention costs per NTD case and infant death averted were I$ 1200 and 11,000, respectively. The cost per DALY averted was I$ 89, 0.8% of Chile's GDP per capita. Taking into account averted costs of care, fortification resulted in net cost savings of I$ 2.3 million. Conclusion Fortification of wheat flour with folic acid is a cost-effective intervention in Chile, a middle income country in the post-epidemiological transition. This result supports the continuation of the Chile fortification program and constitutes valuable information for policy makers in other countries to consider.

Association between CFL1gene polymorphisms and spina bifida risk in a California population

BackgroundCFL1 encodes human non-muscle cofilin (n-cofilin), which is an actin-depolymerizing factor and is essential in cytokinesis, endocytosis, and in the development of all embryonic tissues. Cfl1 knockout mice exhibit failure of neural tube closure at E10.5 and die in utero. We hypothesized that genetic variation within the human CFL1 gene may alter the protein's function and result in defective actin depolymerizing and cellular activity during neural tube closure. Such alterations may be associated with an increased risk for neural tube defects (NTDs).MethodsHaving re-sequenced the human CFL1 gene and identified five common single nucleotide polymorphisms (SNPs) in our target population, we investigated whether there existed a possible association between the genetic variations of the CFL1 gene and risk of spina bifida. Samples were obtained from a large population-based case-control study in California. Allele association, genotype association and haplotype association were evaluated in two different ethnicity groups, non-Hispanic white and Hispanic white.ResultsHomozygosity for the minor alleles of the SNPs studied (rs652021, rs665306, rs667555, rs4621 and rs11227332) appeared to produce an increased risk for spina bifida. Subjects with the haplotype composed of all minor alleles (CCGGT) appeared to have increased spina bifida risk (OR = 1.6, 95% CI: 0.9~2.9), however, this finding is not statistically significant likely due to limited sample size.ConclusionThe sequence variation of human CFL1 gene is a genetic modifier for spina bifida risk in this California population.

Variation and expression of dihydrofolate reductase (DHFR) in relation to spina bifida

The dihydrofolate reductase (DHFR) enzyme is important for folate availability, folate turnover and DNA synthesis. The 19-bp deletion in intron-1 of DHFR has been associated with the risk of having spina bifida affected offspring, supposedly by changing DHFR gene expression. A 9-bp repeat in exon 1 of the mutS homolog 3 ( MSH3) gene was recently demonstrated to be also located in the 5′UTR of DHFR and may possibly affect DHFR gene expression as well. We examined the association between these DHFR variants and spina bifida risk and investigated their effect on DHFR expression. Our study population, consisting of 121 mothers of a spina bifida affected child, 109 spina bifida patients, 292 control women and 234 pediatric controls was screened for the DHFR 19-bp deletion and the DHFR 9-bp repeat. DHFR gene expression was measured in 66 spina bifida patients, using real-time PCR analysis. In this study population, the DHFR 19-bp del/del genotype was not associated with spina bifida risk in mothers and children (OR: 0.8; 95%CI: 0.4–1.5 and OR: 1.2; 95%CI: 0.6–2.2, respectively) and both the WT/del and the del/del genotype did not affect DHFR expression relative to the WT/WT genotype (relative expression = 0.89, p = 0.46 and relative expression = 1.26, p = 0.24, respectively). The DHFR 9-bp repeat was not associated with spina bifida risk in mothers and children. DHFR expression of the 6/6 allele was 73% increased compared to the 3/3 allele, although not significantly (relative expression = 1.73, p = 0.09). We did not find evidence for an effect of the DHFR 19-bp deletion or 9-bp repeat on spina bifida risk in mothers and children. An effect of the 6/6 repeat genotype on DHFR expression cannot be ruled out.

Screening for novel PAX3 polymorphisms and risks of spina bifida

PAX3 plays an important role in mammalian embryonic development. Known mutations in PAX3 are etiologically associated with Waardenburg syndrome and syndromic neural tube defects (NTDs). Mutations in the murine homologue, pax3, are responsible for the phenotype of splotch mice, in which nullizygotes are 100% penetrant for NTDs. The study sample included 74 infants with spina bifida (cases) and 87 nonmalformed infant controls. The conserved paired-box domain as well as the upstream genomic region of PAX3 were subjected to resequencing and those identified SNPs were evaluated as haplotypes. The associations of haplotypes for selected gene regions and the risks of spina bifida were further studied. Nineteen SNPs were observed; 15 observed in controls had been submitted to the National Center for Biotechnology Information (NCBI) database with allele frequencies. The PAX3 gene variant T-1186C (rs16863657) and its related haplotype, TCTCCGCCC of nine SNPs, were found to be associated with an increased risk of spina bifida, with an OR of 3.5 (95% CI: 1.2-10.0) among Hispanic Whites. Our analyses indicated that PAX3 SNPs were not strong risk factors for human spina bifida. However, additional follow-up of the PAX3 gene variant T-1186C (rs16863657) and its related haplotype, TCTCCGCCC, may be important in other populations.

CHKA and PCYT1Agene polymorphisms, choline intake and spina bifida risk in a California population

BackgroundNeural tube defects (NTDs) are among the most common of all human congenital defects. Over the last two decades, accumulating evidence has made it clear that periconceptional intake of folic acid can significantly reduce the risk of NTD affected pregnancies. This beneficial effect may be related to the ability of folates to donate methyl groups for critical physiological reactions. Choline is an essential nutrient and it is also a methyl donor critical for the maintenance of cell membrane integrity and methyl metabolism. Perturbations in choline metabolism in vitro have been shown to induce NTDs in mouse embryos.MethodsThis study investigated whether single nucleotide polymorphisms (SNPs) in human choline kinase A (CHKA) gene and CTP:phosphocholine cytidylytransferase (PCYT1A) gene were risk factors for spina bifida. Fluorescence-based allelic discrimination analysis was performed for the two CHKA intronic SNPs hCV1562388 (rs7928739) and hCV1562393, and PCYT1A SNP rs939883 and rs3772109. The study population consisted of 103 infants with spina bifida and 338 non-malformed control infants who were born in selected California counties in the period 1989–1991.ResultsThe CHKA SNP hCV1562388 genotypes with at least one C allele were associated with a reduced risk of spina bifida (odds ratio = 0.60, 95%CI = 0.38–0.94). The PCYT1A SNP rs939883 genotype AA was associated with a twofold increased risk of spina bifida (odds ratio = 1.89, 95% CI = 0.97–3.67). These gene-only effects were not substantially modified by analytic consideration to maternal periconceptional choline intake.ConclusionOur analyses showed genotype effects of CHKA and PCYT1A genes on spina bifida risk, but did not show evidence of gene-nutrient interactions. The underlying mechanisms are yet to be resolved.

The methionine synthase reductase 66A>G polymorphism is a maternal risk factor for spina bifida

The methionine synthase reductase (MTRR) enzyme restores methionine synthase (MTR) enzyme activity and therefore plays an essential role in homocysteine remethylation. In some studies, the 66A>G polymorphism in the MTRR gene was associated with increased neural tube defect (NTD) risk. Using a case-control design, we studied the association between the MTRR 66A>G polymorphism and spina bifida risk in 121 mothers, 109 spina bifida patients, 292 control women, and 234 pediatric controls. Possible interactions between the MTRR 66A>G variant and the MTR 2756A>G polymorphism, the MTHFR 677C>T variant, plasma vitamin B12, and plasma methylmalonic acid (MMA) levels were examined in the 121 mothers and 292 control women. Meta-analyses were conducted to set the results of the case-control study in the context of eligible literature on the relation between the MTRR 66A>G variant and NTD risk. Finally, a transmission disequilibrium test was performed for 82 complete mother-father-child triads to test for preferential transmission of the MTRR risk allele. In our case-control study, the MTRR 66A>G polymorphism had no influence on spina bifida risk in children [odds ratio (OR) 0.6, 95% confidence interval (CI) 0.4-1.1]. The MTRR 66GG genotype increased maternal spina bifida risk by 2.1-fold (OR 2.1, 95% CI 1.3-3.3). This risk became more pronounced in combination with the MTHFR 677TT genotype (OR 4.0, 95% CI 1.3-12.5). Moreover, we demonstrate a possible interaction between the MTRR 66GG genotype and high plasma MMA levels (OR 5.5, 95% CI 2.2-13.5). The meta-analyses demonstrated that the maternal MTRR 66GG genotype was associated with an overall 55% (95% CI 1.04-2.30) increase in NTD risk and that the MTRR 66GG genotype did not increase NTD risk in children (OR 0.96, 95% CI 0.46-2.01). These data show that the MTRR 66GG genotype is a maternal risk factor for spina bifida especially when intracellular vitamin B12 status is low.

Loss of function polymorphisms in NAT1 protect against spina bifida

Periconceptional folic acid supplementation reduces the risk of having a child with spina bifida. N-acetyltransferase 1 (NAT1) participates in the catabolism of folates and the acetylation of aromatic and heterocyclic amines. Hence, functional polymorphisms in NAT1, the gene encoding NAT1, could influence the risk of spina bifida via either folate catabolism or acetylation of exogenous agents. Individuals with spina bifida and their parents were genotyped for six NAT1 single nucleotide polymorphisms (SNPs) for which the less common allele is associated with reduced or absent enzyme activity (i.e. 97C>T, 190C>T, 559C>T/560G>A, 640T>G and 752A>T). In addition, a "composite" NAT1 genotype was defined as a function of the genotyped SNPs. Descriptive analyses of the SNPs and of the composite genotype indicated that heterozygous parents were more likely to transmit the common allele than the rare allele to their affected offspring. Furthermore, matings of mothers homozygous for the common allele and heterozygous fathers were more common than the reciprocal matings. Log-linear analyses confirmed that both the maternal (P = 0.008) and offspring (P = 0.003) composite NAT1 genotypes were significantly related to the risk of spina bifida. NAT1 variants that reduce or abolish enzyme activity appear to protect against spina bifida, and to exert their influence via both the maternal and the offspring genotypes. These associations may be attributable to a decrease in either folate catabolism or the conversion of exogenous agents to teratogenic derivatives in women and/or developing embryos with a NAT1 genotype that includes a loss of function allele relative to those who do not.

Maternal genotype for the monocyte chemoattractant protein 1 A(‐2518)G promoter polymorphism is associated with the risk of spina bifida in offspring

Maternal genotype for the monocyte chemoattractant protein 1 A(‐2518)G promoter polymorphism is associated with the risk of spina bifida in offspring

Phosphatidylethanolamine N‐methyltransferase (PEMT) gene polymorphisms and risk of spina bifida

Recently, our group demonstrated a reduction in risk of neural tube defects (NTDs) in infants of mothers who had elevated intakes of dietary choline [Shaw et al., 2004]. We hypothesized that disturbance in choline metabolism that are secondary to either a choline deficiency, or choline pathway genes mutations, may represent risk factors for NTDs. Evidence to further support this hypothesis is derived from in vitro studies. These studies showed that inhibition of choline uptake and metabolism during murine neurulation result in growth retardation and developmental defects, including an increase in the prevalence of NTDs in mouse embryos [Fisher et al., 2001, 2002]. Choline or its derivatives, such as acetylcholine, betaine, phosphocholine, phosphatidylcholine (PtdCho), and sphingomyelin, are nutrients critical to many cellular processes. These include the maintenance of the structural integrity of cell membranes, phospholipid biosynthesis, cholinergic neurotransmission, transmembrane signaling, and lipid-cholesterol transport and metabolism. Choline is also one of the major sources of methyl groups in the diet and has essential roles in methyl-metabolism [Zeisel and Blusztajn, 1994]. The phosphatidylethanolamine N-methyltransferase (PEMT, EC 2.1.1.17) pathway contributes approximately one-third of the synthesis of PtdCho, which is the most abundant mammalian phospholipids [Walkey et al., 1999; Reo et al., 2002]. In the absence of dietary supplementation, the PEMT pathway provides the only de novo biosynthesis of choline. This reaction requires S-adenosylmethionine (SAM) as the methyl donor [Bremer and Greenberg, 1961], generating S-adenosylhomocysteine (SAH), which is subsequently hydrolyzed yielding adenosine and homocysteine (Hcy) [Finkelstein, 1998]. In mice, PEMT expression enhances not only plasma Hcy levels, but also Hcy secretion from hepatocytes [Schneider and Vance, 1978]. Hyperhomocysteinemia has been identified as a risk factor for NTDs [Rosenquist and Finnell, 2001]. Knowing the regulatory role of PEMT gene in choline metabolism and ultimately in determining Hcy levels, we examined two non-synonymous SNPs, rs7946 (Met212Val) and rs897453 (Val95Ile). We investigated whether PEMT gene variants would disturb PEMT function, rendering affected individuals more susceptible to spina bifida due to their increased dietary requirements for choline and the dysregulation of Hcy homeostasis. Our analytic strategy investigated potential spina bifida risks associated with PEMT gene polymorphisms in a population-based case-control study.

A population‐based case–control study of risk factors for neural tube defects in four high‐prevalence areas of Shanxi province, China

Shanxi province in Northern China has one of the highest reported prevalence rates of neural tube defects (NTD) in the world. To explore the risk factors for NTDs in Shanxi province, we carried out a population-based case-control study in four selected counties with prevalence rates >10 per 1000 births during 2003. Using a multi-logistic regression model analysis (alpha = 0.10), 158 NTD cases were compared with 226 control mothers. Maternal factors significantly associated with increased risk for an NTD were a primary school education or lower (adjusted odds ratio [OR] 2.32, 95% confidence interval [CI] 1.09, 4.97); a history of a previous birth defect-affected pregnancy (adjusted OR 5.27, 95% CI 0.98, 28.37); history of a fever or 'cold' (adjusted OR 3.36, 95% CI 1.68, 6.72); use of analgesic and antipyretic drugs (adjusted OR 4.89, 95% CI 0.92, 25.97); daily passive exposure to cigarette smoke (adjusted OR 1.60, 95% CI 0.94, 2.73); poor ventilation during heating (adjusted OR 3.91, 95% CI 0.75, 20.81); and consumption of >or= six meals per week containing pickled vegetables (adjusted OR 3.86, 95% CI 1.11, 13.47) during pregnancy. Factors which appeared to be protective were meat consumption one to three times per week (adjusted OR 0.62, 95% CI 0.37, 1.06), or >or= four times per week (adjusted OR 0.28, 95% CI 0.11, 0.77); and legume consumption >or= six times per week (adjusted OR 0.39, 95% CI 0.17, 0.89). Differences in risk were found between the two most common phenotypes, anencephaly and spina bifida. Most of the environmental factors had stronger positive and negative associations with risk for anencephaly rather than spina bifida, whereas history of a previous birth defect-associated pregnancy, as well as legume consumption, were more strongly associated with the risk for spina bifida than for anencephaly. The findings suggest that aetiological heterogeneity may exist between anencephaly and spina bifida.

Congenital structural anomalies in offspring of women with epilepsy—a population-based cohort study in Finland

Offspring of women with epilepsy may have an increased risk for congenital malformations, probably attributable to maternal antiepileptic medication. We conducted this population-based study to obtain valid and accurate estimates on major congenital malformations in the offspring of women with epilepsy, based on a large and representative patient cohort. We identified all women (n = 6,535) entitled to full reimbursement for antiepileptic medication indicated for epilepsy for the first time between 1985 and 1994 from the Social Insurance Institution of Finland database. A reference cohort (n = 14,704) was identified from the Finnish Population Register Centre. Information on children born between 1993 and 2000 (patient cohort, n = 2,162; reference cohort, n = 5,413) was obtained from the Medical Birth Register. Information on children born with malformation (patient cohort, n = 116; reference cohort, n = 151) was obtained from the Finnish Register of Congenital Malformations. The prevalence of major malformation was 54/1,000 births among patients with epilepsy and 28/1,000 births among mothers without epilepsy, corresponding to a 2-fold overall risk for malformation in the offspring of women with epilepsy. The risk for spina bifida [odds ratio (OR) = 11.3, 95% confidence interval (CI) 2.34-108] and congenital anomalies of genital organs (OR = 8.38, 95% CI 2.15-47.4) was substantially elevated in the offspring of mothers with epilepsy. The absolute excess in the prevalence of major malformations was 26/1,000 births in the offspring of mothers with epilepsy in relation to the offspring of reference mothers. The highest relative risk was observed in spina bifida and congenital anomalies of genital organs. However, these malformations cover only a small proportion of all major malformations.

A known functional polymorphism (Ile120Val) of the human PCMT1 gene and risk of spina bifida

Folate binding protein 1 ( Folr1) knockout mice with low maternal folate concentrations have been shown to be excellent animal models for human folate-responsive neural tube defects (NTDs). Previous studies using the Folr1 knockout mice revealed that maternal folate supplementation up-regulates the expression of the PCMT1 gene in Folr1 nullizygous neural tube tissue during neural tube closure. PCMT1 encodes the protein repair enzyme l-isoaspartate ( d-aspartate) O-methyltransferase (PIMT) that converts abnormal d-aspartyl and l-isoaspartyl residues to the normal l-aspartyl form. PIMT is known to protect certain neural cells from Bax-induced apoptosis. Pcmt1-deficient mice present with abnormal AdoMet/AdoHcy homeostasis. We hypothesized that a known functional polymorphism (Ile120Val) in the human PCMT1 gene is associated with an increased risk of folate-responsive human NTDs. A case-control study was conducted to investigate a possible association between this polymorphism and risk of spina bifida. Compared to the Ile/Ile and Ile/Val genotypes, the homozygous Val/Val genotype showed decreased risk for spina bifida (adjusted odds ratio = 0.6, 95% confidence interval: 0.4–0.9). Our results showed that the Ile120Val polymorphism of PCMT1 gene is a genetic modifier for the risk of spina bifida. Val/Val genotype was associated with a reduction in risk for spina bifida.

Analysis ofALDH1A2,CYP26A1,CYP26B1,CRABP1, andCRABP2 in human neural tube defects suggests a possible association with alleles inALDH1A2

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. 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. 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. These results may suggest that polymorphisms in ALDH1A2 may influence the risk for lumbosacral myelomeningocele in humans.

Genes encoding catalytic subunits of protein kinase a and risk of spina bifida

PRKACA and PRKACB are genes encoding the cAMP-dependent protein kinase A (PKA) catalytic subunits alpha and beta, respectively. PKA is known to be involved in embryonic development, as it down-regulates the Hedgehog (Hh) signaling pathway, which is critical to normal pattern formation and morphogenesis. The PKA-deficient mouse model, which has only a single catalytic subunit, provided intriguing evidence demonstrating a relationship between decreased PKA activity and risk for posterior neural tube defects (NTDs) in the thoracic to sacral regions of gene-knockout mice. Unlike most other mutant mouse models of NTDs, the PKA-deficient mice develop spina bifida with 100% penetrance. We hypothesized that sequence variations in human genes encoding the catalytic subunits may alter the PKA activity and similarly increase the risk of spina bifida. We sequenced the coding regions and the exon/intron boundaries of PRKACA and PRKACB. We also examined 3 common single-nucleotide polymorphisms (SNPs) of these 2 genes by allele discrimination. Five sequence variants in coding region and 2 intronic sequence variants proximal to exons were detected. None of the 3 SNPs examined in the association study appeared to be associated with substantially increased risk for spina bifida. Our results did not reveal a strong association between these PKA SNPs and spina bifida risk. Nonetheless, it is important to examine the possible gene-gene interactions between PRKACA and PRKACB when evaluating the risk for NTDs, as well as genes encoding regulatory subunits of PKA. In addition, interactions with other genes such as Sonic Hedgehog (SHH) should also be considered for future investigations.

The NAT1 C1095A polymorphism, maternal multivitamin use and smoking, and the risk of spina bifida

The risk of having a child with a neural tube defect (NTD) can be reduced by maternal, periconceptional supplementation with folic acid, but the underlying folate-dependent protective mechanism remains unclear. N-acetyltransferase 1 is involved in acetylation of aromatic and heterocyclic amines and the catabolism of folates. Hence, functional polymorphisms in NAT1, the gene encoding N-acetyltransferase 1, are plausible risk factors for NTDs. Such variants could exert an influence on the risk of NTDs via their role in acetylation or folate catabolism and could act through the maternal or the embryonic genotype. NAT1 C1095A genotypes and information on maternal, periconceptional multivitamin use and smoking were obtained as part of a family-based study of spina bifida. Associations between spina bifida and the embryonic and maternal NAT1 C1095A genotypes, and potential NAT1 C1095A genotype-exposure interactions were evaluated using log-linear modeling. The analyses provided no evidence that the embryonic or maternal NAT1 C1095 genotypes influence the risk of spina bifida independently, or through interactions with maternal use of multivitamins. There was evidence that the embryonic, and possibly the maternal, NAT1 C1095A genotype influence the risk of spina bifida via interactions with maternal smoking status. The genotype for the NAT1 C1095A polymorphism does not appear to be an independent risk factor for spina bifida. However, the results of these analyses provide preliminary evidence that this polymorphism may be associated with the risk of spina bifida in the offspring of women who smoke during early pregnancy.