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.     

Methylenetetrahydrofolate reductase enzyme polymorphisms as maternal risk for Down syndrome among Turkish women

Advanced maternal age is the only fully accepted risk factor for trisomy 21, while most children with Down syndrome (DS) are born to younger mothers (<35 years). The relationship between chromosomal nondisjunction leading to aneuploidy and folate metabolism has drawn attention in the recent years. In this study, we examined the two polymorphisms in genes encoding the folate metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR), namely, 677C > T and 1298A > C. The prevalence of these variant genotypes in mothers of DS children (case mothers) (n = 152) was compared with controls (n = 91). Frequencies of MTHFR 677C > T genotypes (CC, CT, and TT) and also combination of heterozygous and homozygous variant genotypes (CT or TT) (P = 0.28) demonstrated no difference between the case and control groups. Genotype frequencies of MTHFR 1298A > C (AA, AC, and CC) were similar among the case and control mothers. Variant genotypes of MTHFR 1298A > C (AC or CC) were also insignificant when compared between the two groups. This is yet the largest case-control study conducted for MTHFR 677C > T and also the first to investigate a possible relation with MTHFR 1298A > C. The data presented in this study fail to support the relationship between MTHFR 677C > T and 1298A > C polymorphisms and risk of having a child with DS.     

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.     

Methylenetetrahydrofolate reductase gene polymorphisms and the risk of anencephaly in Mexico

The precise etiology of neural tube defects (NTDs) is not known. There is some evidence that mutations in MTHFR gene provide susceptibility to NTDs in some populations; however, other studies have not found this association. One of the problems with previous studies is that they treat NTDs as a homogeneous group, when specific defects could have different etiologies. We conducted a case-control study specifically for anencephaly, based on the Mexican Epidemiological Surveillance System of Neural Tube Defects to evaluate its association with maternal MTHFR 677C > T and 1298A > C polymorphisms, in three states with high frequencies of NTDs: Puebla, Estado de México and Guerrero. We interviewed and collected blood samples from 118 case mothers and 112 control mothers. The questionnaire included information on their reproductive history, socioeconomic characteristics, prenatal care, tobacco and alcohol use, presence of chronic diseases, acute illnesses and fever, consumption of multivitamins and drugs during the periconceptional period. After adjusting for potential confounders, the risk from the mutated homozygous mothers (677TT genotype) was significantly higher than that from mothers with 677CC genotype (OR 3.16, 95% CI 1.29-7.73); in the case of the heterozygous mothers, an increased risk of anencephaly was observed, even though this was not statistically significant (OR 1.81 95% CI 0.78-4.25). The association found between maternal 677TT genotype and anencephaly and the elevated presence of the 677T allele among Mexican women of fertile age urges intensifying folic acid supplementation which has proved to modify this genetic risk in other populations.     

Predisposition to spina bifida: Search for a relation to maternal gastric acid secretion.

The peak acid output of the stomach in a group of 71 mothers of spina bifida children and in 71 matched controls was estimated indirectly by the serum level of group I pepsinogens. The mean levels did not differ significantly, suggesting that the conjectured teratogen is not specially acid-labile. The variance was significantly higher in index subjects than in controls, but the interpretation of this finding is not clear.     

May spina bifida result from an X-linked defect in a selective abortion mechanism?

It is suggested that the major genetic factor in determining the birth of children with neural tube defects may be a single X-linked gene. It acts as an X-linked dominant, not by producing neural tube defects, but by enabling the affected fetus to survive selective spontaneous abortion. This mechanism, mediated at the deciduoplacental junction, may be under the control of both maternal and fetal genes. With more mutant alleles, survival would become more likely, reaching a maximum in the homozygous affected female fetus of a homozygous affected mother. The female excess in anancephaly is greater than that in spina bifida because of its prenatal severity, thus requiring relatively more mutant alleles for survival.     

Elevated levels of alfa fetoprotein in maternal serum and amniotic fluid in two cases of spina bifida

Therapeutic abortions were performed in two cases of spina bifida which were diagnosed by determination of the lafa fetoprotein levels in the amniotic fluid and maternal serum.     

The C677T mutation of the 5,10-methylenetetrahydrofolate reductase gene is a moderate risk factor for spina bifida in Italy.

OBJECTIVE: To estimate the risk for spina bifida associated with the common mutation C677T of the MTHFR gene in a country with a relatively low prevalence of NTDs. DESIGN: Case-control study. SUBJECTS: Cases: 203 living patients affected with spina bifida (173 myelomeningocele and 30 lipomeningocele); controls: 583 subjects (306 young adults and 277 unselected newborns) from northern and central-southern Italy. SETTING: Cases: three spina bifida centres; young adult controls: DNA banks; newborn controls: regional neonatal screening centres. MAIN OUTCOME MEASURES: Prevalence of the C677T genotypes in cases and controls by place of birth; odds ratios for spina bifida and estimated attributable fraction. RESULTS: The prevalence of T/T, T/C, and C/C genotype was 16.6%, 53.7%, and 29.7% in controls and 25.6%, 43.8%, and 30.6% in cases, respectively. We found no differences between type of defect or place of birth. The odds ratio for spina bifida associated with the T/T genotype v C/C plus T/C was 1.73 (95% CI 1.15, 2.59) and the corresponding attributable fraction was 10.8%. No increased risk was found for heterozygous patients (OR=0.79, 95% CI 0.53-1.18). CONCLUSION: This study, as well as the meta-analysis we updated, shows that homozygosity for the MTHFR C677T mutation is a moderate risk factor in Europe, and even in Italy where there is a relatively low prevalence of spina bifida. The estimated attributable fraction associated with this risk factor explains only a small proportion of cases preventable by periconceptional folic acid supplementation. Thus, other genes involved in folate-homocysteine metabolism, their interaction, and the interaction between genetic and environmental factors should be investigated further.     

Polymorphisms in DNA repair genes as risk factors for spina bifida and orofacial clefts

Repairing DNA damage is critical during embryogenesis because development involves sensitive periods of cell proliferation, and abnormal cell growth or death can result in malformations. Knockout mouse experiments have demonstrated that disruption of DNA repair genes results in embryolethality and structural defects. Studies using mid-organogenesis rat embryos showed that DNA repair genes were variably expressed. It is hypothesized that polymorphisms that alter the functionality of DNA repair enzymes may modify the risk of malformations. We conducted a case-control analysis to investigate the relationship between DNA repair gene polymorphisms and the risk of spina bifida and oral clefts. Newborn screening blood spot DNA was obtained for 250 cases (125 spina bifida, 125 oral clefts) identified by the California Birth Defects Monitoring Program, and 350 non-malformation controls identified from birth records. Six single nucleotide polymorphisms of five DNA repair genes representing three distinct repair pathways were interrogated including: XRCC1 (Arg399Gln), APE1 (Asp148Glu), XRCC3 (Thr241Met), hOGG1(Ser326Cys), XPD (Asp312Asn, Lys751Gln). Elevated or decreased odds ratios (OR, adjusted for race/ethnicity) for spina bifida were found for genotypes containing at least one copy of the variant allele for XPD [751Gln, OR = 1.62; 95% confidence interval (CI) = 1.05-2.50] and APE 148 (OR = 0.58; CI = 0.37-0.90). A decreased risk of oral clefts was found for XRCC3 (OR = 0.62; CI = 0.39-0.99) and hOGG1 (326 Cys/Cys, OR = 0.22; CI = 0.06-0.78). This study suggested that polymorphisms of DNA repair genes, representing different major repair pathways, may affect risk of two major birth defects. Future, larger studies, examining additional repair genes, birth defects, and interaction with exposures are recommended.     

Genetic variation in biotransformation enzymes,air pollution exposures,and risk of spina bifida

Spina bifida is a birth defect characterized by incomplete closure of the embryonic neural tube. Genetic factors as well as environmental factors have been observed to influence risks for spina bifida. Few studies have investigated possible gene‐environment interactions that could contribute to spina bifida risk. The aim of this study is to examine the interaction between gene variants in biotransformation enzyme pathways and ambient air pollution exposures and risk of spina bifida. We evaluated the role of air pollution exposure during pregnancy and gene variants of biotransformation enzymes from bloodspots and buccal cells in a California population‐based case‐control (86 cases of spina bifida and 208 non‐malformed controls) study. We considered race/ethnicity and folic acid vitamin use as potential effect modifiers and adjusted for those factors and smoking. We observed gene‐environment interactions between each of the five pollutants and several gene variants: NO (ABCC2), NO₂ (ABCC2, SLC01B1), PM₁₀ (ABCC2, CYP1A1, CYP2B6, CYP2C19, CYP2D6, NAT2, SLC01B1, SLC01B3), PM_2.5 (CYP1A1 and CYP1A2). These analyses show positive interactions between air pollution exposure during early pregnancy and gene variants associated with metabolizing enzymes. These exploratory results suggest that some individuals based on their genetic background may be more susceptible to the adverse effects of pollution.     

Shifting genetic patterns in anencephaly and spina bifida.

The long-term decline in the incidence of the neural tube malformations, anencephaly and spina bifida (ASB), ended in the mid-1950's in New York State. Since that time, the rate of these birth defects has remained between 1 and 1.5/1000 births. In this low incidence population, we tested the basic tenets which support a genetic aetiology. We found that the full sib recurrence rate (1.8%) was higher than the half sib recurrence rate (0.8%) and the twin concordance rate (6.8%) was higher than the full sib recurrence rate. We found the incidence of ASB in twins to be the same as the incidence of ASB in singletons. Our findings are compatible with polygenic inheritance aetiology for ASB. The genetic molecular pathway of these birth defects may be identifiable through biochemical screening of families with one or more ASB children.     

Attention and executive functions in adolescents with spina bifida

OBJECTIVE: This study was designed to examine attention processes and executive functioning in adolescents with spina bifida, and to explore whether impairment in these domains contributes to problems with social adjustment. METHODS: A sample of adolescents with spina bifida (n = 68) and a matched comparison group (n = 68) and their families were followed longitudinally. All participants completed questionnaires, and the adolescent participants underwent neurocognitive testing. RESULTS: The spina bifida sample showed greater impairment on objective and subjective measures of attention and executive functioning, even when differences in intellectual functioning were controlled. Additionally, attention and executive deficits were found to be predictive of social adjustment difficulties. A mediational analysis suggested the neurocognitive deficits mediate associations between spina bifida status and social adjustment difficulties. CONCLUSIONS: Adolescents with spina bifida appear to exhibit clear impairment in attention and executive functioning and this impairment may contribute to their well-established social difficulties.     

Degree of genetic homozygosity and distribution of AB0 blood types among patients with spina bifida occulta and spina bifida aperta

Introduction

Assuming that spina bifida (SB) is a genetically controlled disease, the aim of our study was to evaluate the degree of genetic homozygosity and the distribution of AB0 blood types among patients with SB occulta and SB aperta by the homozygously recessive characteristics (HRC) test.

Material and methods

Our study included an analysis of the presence, distribution and individual combination of 15 selected genetically controlled morpho-physiological traits in a sample of 100 patients with SB (SB occulta N = 50 and SB aperta N = 50) and a control group of individuals (N = 100).

Results

We found a statistically significant difference between the mean values for genetic homozygosity (SB 4.5 ±0.3; control 3.0 ±0.2, p < 0.001) and also differences in the presence of certain individual combinations of such traits. In 12 (80.0%) of the 15 observed characteristics, recessive homozygosity was expressed to a greater degree among the group of SB patients, while for 9 (60.0%) of the traits this level of difference was statistically significant (Σ_χ ² = 266.3, p < 0.001). There was no difference in average homozygosity of such genetic markers between groups of SB occulta and SB aperta patients, but the type of individual variation in the two studied groups significantly differed. In the group of patients with SB the frequency of 0 blood group was significantly increased while B blood group was significantly decreased.

Conclusions

Our results clearly show that there is a populational genetic difference in the degree of genetic homozygosity and variability between the group of patients with SB and individuals without clinical manifestations, indicating a possible genetic component in the aetiopathogenesis of spina bifida.