5,10 Methylenetetrahydrofolate reductase genetic polymorphism as a risk factor for neural tube defects

Persons with a thermolabile form of the enzyme 5,10 methylenetetrahydrofolate reductase (MTHFR) have reduced enzyme activity and increased plasma homocysteine which can be lowered by supplemental folic acid. Thermolability of the enzyme has recently been shown to be caused by a common mutation (677C^→T) in the MTHFR gene. We studied 41 fibroblast cultures from NTD-affected fetuses and compared their genotypes with those of 109 blood specimens from individuals in the general population. 677C^→T homozygosity was associated with a 7.2 fold increased risk for NTDs (95% confidence interval: 1.8–30.3; p value: 0.001). These preliminary data suggest that the 677C^→T polymorphism of the MTHFR gene is a risk factor for spina bifida and anencephaly that may provide a partial biologic explanation for why folic acid prevents these types of NTD.     

Associated malformations among infants with neural tube defects

Infants with neural tube defects (NTDs) often have associated congenital anomalies. The reported frequency and types of associated malformations vary between different studies. The purpose of this investigation was to assess the frequency and types of associated malformations among infants with NTDs in a geographically well-defined population from 1979 to 2008 of 402,532 consecutive births. Of the 441 infants with NTDs born during this period, 20.4% had associated malformations. Infants with associated malformations were divided into those with recognizable conditions [11 (2.5%) infants with chromosomal and 23 (5.2%) with non-chromosomal conditions], and those without recognizable conditions [56 (12.7%) infants with multiple malformations]. Associated malformations were more frequent among infants with encephalocele (36.8%) than those with anencephaly (11.5%) or spina bifida (23.8%). Oral clefts and malformations in the musculoskeletal, renal and cardiovascular systems were the most commonly observed associated anomalies. The frequency of associated malformations in infants with NTDs emphasizes the need for a thorough investigation of these infants. Routine screening for other malformations, especially facial clefts and musculoskeletal, renal and cardiac anomalies, may need to be considered in infants with NTDs, and referral of these infants for genetics evaluation and counseling seems warranted.     

Molecular genetic analysis of the gene encoding the trifunctional enzyme MTHFD (methylenetetrahydrofolate-dehydrogenase, methenyltetrahydrofolate-cyclohydrolase, formyltetrahydrofolate synthetase) in patients with neural tube defects

It is now well recognized that periconceptional folic acid or folic acid containing multivitamin supplementation reduces the risk of neural tube defects (NTDs). Recently we were able to show that homozygosity for a thermolabile variant of the enzyme methylenetetrahydrofolate reductase is associated with an increased risk for spina bifida in patients recruited from the Dutch population. However, this genetic risk factor could not account for all folic acid preventable NTDs. In an attempt to identify additional folate related enzymes that contribute to NTD etiology we now studied the methylenetetrahydrofolate dehydrogenase gene on chromosome 14q24 which encodes a single protein with three catalytic properties important in the folate metabolism. The cDNA sequence of 38 familial and 79 sporadic patients was screened for the presence of mutations by single strand conformation polymorphism (SSCP) analysis followed by sequencing. Two amino acid substitutions were identified. The first one (R293H) was detected in a patient with familial spina bifida and not in 300 control individuals. The mutation was inherited from the unaffected maternal grandmother and was also present in two younger brothers of the index patient, one of them displaying spina bifida occulta and the other being unaffected. The second change turned out to be an amino acid polymorphism (R653Q) that was present in both patients and controls with similar frequencies. Our results so far provide no evidence for a major role of the methylenetetrahydrofolate-dehydrogenase (MTHFD) gene in NTD etiology. However, the identification of a mutation in one family suggests that this gene can act as a risk factor for human NTD.     

PRKCI基因单核苷酸多态性与神经管畸形的相关性研究

目的探讨PRKCI基因单核苷酸多态性（SNP）与中国山西省神经管畸形（NTDs）发生的相关性。方法采用病例对照研究,利用MassARRAY分子量阵列分析平台,检测133例NTDs标本和135例非病理性胎儿标本PRKCI基因中17个标签SNPs的基因分型,分析其与NTDs发生的相关性。结果 17个SNPs位点中,16个的微效等位基因频率（MAF）与HapMap或dbSNP数据库的结果基本一致。除rs9876082外,其余SNPs位点的基因型分布和等位基因频率在病例组和对照组均无明显差异。rs9876082位点为纯合的微效等位基因A时,NTDs的发病率增加（P=0.035,比值比=2.135,95%可信区间=1.846-2.471）,但是调整其它变量后进行logistic回归分析,这种相关性不再明显（P=0.057）。结论 PRKCI基因rs9876082位点与NTDs的发生有弱的相关性,这种相关性需进一步加大样本进行验证,PRKCI基因可能不是通过其SNPs影响NTDs的易感性。     

Is disordered folate metabolism the basis for the genetic predisposition to neural tube defects?

Vitamin levels were measured in twenty women under 35 years of age with a history of two or more neural tube defect pregnancies. Each index case was compared with a female control matched for age, obstetric history and social class. The mean concentration of red cell folate in the subjects was 178 ng/ml, significantly lower than the mean of 268 ng/ml for the control group (P = 0.005). Red cell folate levels showed a linear relationship with the number of neural tube defect pregnancies, the levels being lowest in women who had had three or four affected offspring. There was no significant difference in serum folate; plasma or white cell vitamin C; plasma vitamin A; thiamine, riboflavine or pyridoxine status; serum vitamin B12; plasma vitamin E; total protein, albumin, transferrin, magnesium, copper or zinc. Diet was assessed by a questionnaire. The dietary intakes of total folate and other vitamins except vitamin A were lower in the subjects than the controls but none of the differences were statistically significant. Regression analysis showed a difference between subjects and controls in the relationship of red cell folate to dietary folate. This study demonstrates an association between susceptibility to offspring with neural tube defects and depressed red cell folate levels which cannot be entirely attributed to a lower dietary intake of folate. It is postulated that one factor predisposing to the occurrence of neural tube defects may be an inherited disorder of folate metabolism.     

Sex,neural tube defects,and multisite closure of the human neural tube

While neural tube defects (NTD) overall have a female sex bias, this does not apply to all sites along the neuraxis. The findings regarding sex and NTD in a series of midtrimester fetuses are reviewed, and then analysed in terms of the recent hypothesis that during embryogenesis of the human neural tube there are multiple closure sites, rather than a single zipping up process. Females more often than males tend to have craniorachischisis, spina bifida involving the thorax, the holoacrania form of anencephaly, anencephaly and cervical spina bifida and encephalocoeles, while males more often than females have spina bifida affecting the lower spine. Meroacrania occurs equally in both sexes. Other sources indicate that there is a male bias in frontoethmoidal encephalocoeles. Since sex seems to be a factor that is differentially associated with lack of closure of specific areas of the neural tube, it would seem to support the notion that there are multiple closure sites in the human neural tube. However, no association was found between a particular sex and either the type of NTD which have an isolated abnormality or those NTD associated with developmental abnormalities of other body systems. © 1995 Wiley-Liss, Inc.     

Multi-site neural tube closure in humans and maternal folate supplementation

A group of 13 individuals with neural tube defects (NTD) despite maternal periconceptional folate supplementation was examined to determine precisely which closure sites along the neural tube had failed during embryogenesis. All the common forms of NTD, and thus all the usual closure sites, were represented. This suggests that folate deficiency does not act specifically on one region of the neural tube; rather, it may be more generally involved in the cause of human NTD. © 1995 Wiley-Liss, Inc.     

Multigeneration maternal transmission in Italian families with neural tube defects

Periconceptional vitamin supplementation with folate prevents about three-quarters of expected cases of neural tube defects (NTDs) in clinical trials. However, vitamin action may be regulated at the level of the gene, and individual susceptibility to environmental agents, including dietary components, also may be under genetic control. We investigated the presence of familial factors in a retrospective case control study of neural tube defects in Genoa, Italy. Cases included all patients treated at a single pediatric neurosurgical service. Controls matched on age and sex came from the same hospital. We found strong evidence for the contribution of genetic factors in this study. There was an excess risk of 14 for the occurrence of NTDs in first-degree relatives compared to controls (P < .0005). There was no difference in sex ratio in any group of relatives, but maternal grandparents of children with a high spinal lesion had 14% fewer offspring than paternal grandparents (P < .005), possibly because of excess miscarriages. Our study is the first to show complex patterns of inheritance in spina bifida families affecting three generations in one clinical subgroup and preferentially on the mother's side. These results support a role for genomic imprinting and highlight the value of multidisciplinary epidemiologic and clinical studies that include multiple generations. New studies incorporating dietary and genetic approaches will help clarify and extend these findings. © 1996 Wiley-Liss, Inc.     

Risk factors associated with neural tube defects

Spina bifida represents a broad category of neural tube defects (NTD) which affects approximately 1–4/1,000 live births. Since effective prenatal diagnostic testing for 90 % of NTD is available through measurement of alpha-fetoprotein (AFP) in amniotic fluid, ascertainment of high risk factors associated with the occurrence of NTD would be both desirable and important. At the present time, generally, the major indication for prenatal testing for NTD is the presence of a first-degree relative with some form of NTD. To date, few other factors have been utilized to identify a family as "at risk".
We have studied a group of 19 families of 10 female and 9 male index cases with NTD. The parents of each index case were interviewed and pedigrees were prepared on each family. Conditions screened for in these families included spina bifida and other NTD, pilonidal cysts, scoliosis, kyphosis and other vertebral disorders which were hypothesized to be possibly related to NTD. There were 58 first-, 171 second-, and 802 third-degree relatives screened in this study. This sample population was similarly characteristic with regard to sex, maternal age and birth order distributions as compared to previous populations of NTD described and was therefore considered to be representative. Our results indicate that: (1) pilonidal cysts are 6 times more frequent in the fathers and twice as frequent in the mothers of children with spina bifida than in the general population;
These preliminary studies suggest that several minor clinical conditions in parents may be important to consider as possible risk signs suggesting couples be considered for prenatal evaluation for the prevention of NTD.     

Fetal mortality in sibships of cases with neural tube defects

It has been suggested that rates of fetal mortality in sibships of probands with a malformation inherited as a multifactorial threshold trait may reflect their liability to the malformation. If so, spontaneous abortion rates should be more frequent in sibships thought to have greater liability. For anencephaly and spina bifida (ASB), then, spontaneous abortion should be higher in the sibships of male probands and in families with more than one affected case (multiplex families). This hypothesis was tested using data on cases from The Montréal Children's Hospital and from the literature. Approximately 5000 pregnancies were analyzed. Rates of abortion did not vary with the sex or diagnosis of the proband. The spontaneous abortion rate was slightly higher in multiplex than in simplex families, but the difference was not statistically significant and most likely reflects the differing reproductive patterns in the two types of families. Thus, if male probands and multiplex sibships do have, on average, more liability for ASB, this liability cannot be detected in spontaneous abortion rates in the sibships available for this analysis.     

Screening for coeliac disease as a possible maternal risk factor for neural tube defect

Coeliac disease is an important cause of malabsorption, particularly of folic acid, in adults. We investigated the possibility that it might be a maternal risk factor for neural tube defect (NTD)-associated pregnancy by screening affected mothers using serum endomysial antibody (EmA) which has high sensitivity and specificity for coeliac disease. One (1.6%) of 60 patients was EmA positive and had a diagnosis of coeliac disease confirmed by the finding of villous atrophy on jejunal biopsy. In conclusion, the majority of NTD-associated pregnancies are not associated with maternal coeliac disease and our study is additional evidence that abnormalities of folic acid metabolism rather than absorption are the most important risk factors for NTD. Further studies are needed to determine whether the coeliac disease prevalence among women with NTD-affected pregnancy is higher than that of the general population.     

Studies in neural tube defects I. Epidemiologic and etiologic aspects

In the NIH Collaborative Perinatal Project, a prospective study of over 53,000 pregnant women and their offspring, 71 single-born children (13.33/10,000) were found to have a non-syndromal neural tube defect (NTD). A family history was present in only one case. The group of individuals with NTD was compared to a group of 400 randomly selected non-malformed control infants. Of over 50 maternal factors studied the following showed significant association with NTD in the offspring: diabetes mellitus; organic heart disease; lung disease; and diuretic, antihistamine, and sulfonamide use. The interval between the termination of the immediately previous pregnancy and the start of the proband pregnancy was significantly shorter in mothers of NTD children than in mothers of control infants. The risk for NTD was also significantly increased if the immediately previous pregnancy was a spontaneous abortion. There was no increased risk for NTDs among sibs of children with major malformations such as tracheo-esopha-geal “dysraphism,” cleft lip/palate, or renal agenesis. NTDs are apparently etiologically heterogeneous.     

Amniotic fluid folate, vitamin B12 and transcobalamins in neural tube defects

Levels of folate, vitamin B12, the vitamin B12 binding proteins, apotranscobalamin I, II and III (TC I, II and III) and the unsaturated vitamin B12 binding capacity (UBBC) were measured in mid-trimester amniotic fluids from normal pregnancies, and from those where the fetus had open spina bifida, anencephaly or omphalocoele, and where the fetus was normal but the mother had had a previous neural tube defect pregnancy. At 15-19 weeks' gestation, vitamin B12 levels were low in the fluids of all the types of abnormal fetuses, and also of normal fetuses where there had been a previous NTD sib. In contradistinction, TC I, II and III and UBBC levels were generally abnormally high in all these groups. Low vitamin B12 levels in the face of high carrier protein levels suggest deranged vitamin B12 production or transport. Since these abnormalities are present in fluids from normal sibs of NTD individuals as well as from those with midline lesions, an inherited defect is implied. We propose that at least part of the genetic predisposition to NTD, and possibly other midline defects, could reside in an abnormality connected with vitamin B12 production, transport or metabolism, and a mechanism is suggested.     

Nutritional patterns of mothers of children with neural tube defects in Newfoundland

In an exploratory study of the genetic epidemiology of neural tube defects in Newfoundland, we studied mothers who had given birth to a child with a neural tube defect (NTD) with respect to their nutrition, as well as various other factors. The frequency of NTD in the area studied was 3.5/1,000 births and has not decreased recently, as it has in some other parts of the world. Twenty-five mothers of children with NTD and a comparison group (CG), matched for age and neighbourhood, completed 3 day dietary records. The NTD group consisted of all mothers who had given birth to an NTD child within the previous 3.5 years in the chosen area. The CG mothers were ascertained through the local public health nurse who chose the nearest unaffected child born in the same time period as the NTD probands. NTD mothers were younger, heavier, and of lower socioeconomic status than were CG mothers. CG group women consumed more vitamin supplements during the periconceptional period (P<0.05) and consumed more dairy and cereal products, fruits and vegetables (other than potatoes), and fewer sweets than did NTD mothers. Sixty-four percent of NTD mothers had folacin intakes below the recommended level (168 mg) compared to 27% of CG mothers (P<0.01). These findings support previous evidence that poor maternal nutrition, and low dietary folate in particular, increase the chance of having a child with an NTD, and emphasize the need for supplementary folate in the diet of women of childbearing age in areas where the frequency of NTDs is high. © 1995 Wiley-Liss, Inc.     

神经管畸形患儿还原叶酸载体基因和叶酸之间交互作用

目的 探讨神经管畸形(neural tube defects,NTDs)患儿还原叶酸载体基因(reduced folate carrier gene,RFCI）A80G多态性与母亲孕早期未增补叶酸之间的关联性,为寻找NTDs危险因素的遗传易感标志物提供流行病学依据。方法采用限制性片段长度多态性-聚合酶链反应方法,对104个NTDs患儿及其母亲和100名正常儿童及其母亲的外周血DNA进行RFCI第80位单核苷酸多态性检测,通过病例对照研究,调查了后代RFCI A80G基因型与母亲孕期前后增补叶酸之间的基因环境交互作用。结果 RFCI GG基因型的子代发生NTDs危险高于AA基因型子代(OR=2．56,95％CI=1．04～6．36);母亲孕早期不增补叶酸,生育NTDs的危险高于增补叶酸的母亲(OR=7．69,95％CI=2．86～21．75);母亲孕期未增补叶酸,其子代GG基因型,发生NTDs的危险是AA基因型的3．30倍(95％CI=1．15～9．65);在叶酸和RFCI基因交互作用研究中,母亲未增补叶酸和子代GG基因型同时存在,发生NTDs的危险是8．80(95％CI=2．86～29．82),交互作用系数为1．45,,结论 在中国人群中,RFCI GG基因型可能是NTDs发生的遗传易感基因之一,子代RFCI GG基因型与母亲孕期叶酸缺乏之间存在交互作用,可能增加NTDs的发病危险。