Will increasing folic acid in fortified grain products further reduce neural tube defects without causing harm?: consideration of the evidence

To reduce neural tube defects (NTDs), the U.S. Food and Drug Administration (FDA) mandated that by January 1998 all enriched grain products should contain 140 microg of folic acid (FA)/100 g of flour. Groups concerned with optimal prevention of NTDs had argued that the level should be 350 microg/100 g. However, when it appeared that the debate might delay implementation of any fortification, these groups petitioned the FDA to implement fortification at the originally proposed level of 140 microg/100 g, anticipating that the FDA might consider increasing the level at a later time. Mandated FA fortification (FAF) has now been in place in the United States for 9 y. The impact of this important public health intervention on NTD rates, the possible benefit to other disease conditions, and potential harms have been evaluated. As background for a possible request that the FDA consider increasing FAF, evidence bearing on the question of whether an increase can further reduce NTD births without causing harm is reviewed here. The published data indicate that it is appropriate that the FDA conduct or commission a balanced analysis of the evidence by scientists who will act on that evidence to decide this important question.     

Etiology, pathogenesis and prevention of neural tube defects

Spina bifida, anencephaly, and encephalocele are commonly grouped together and termed neural tube defects (NTD). Failure of closure of the neural tube during development results in anencephaly or spina bifida aperta but encephaloceles are possibly post-closure defects. NTD are associated with a number of other central nervous system (CNS) and non-neural malformations. Racial, geographic and seasonal variations seem to affect their incidence. Etiology of NTD is unknown. Most of the non-syndromic NTD are of multifactorial origin. Recent in vitro and in vivo studies have highlighted the molecular mechanisms of neurulation in vertebrates but the morphologic development of human neural tube is poorly understood. A multisite closure theory, extrapolated directly from mouse experiments highlighted the clinical relevance of closure mechanisms to human NTD. Animal models, such as circle tail, curly tail, loop tail, shrm and numerous knockouts provide some insight into the mechanisms of NTD. Also available in the literature are a plethora of chemically induced preclosure and a few post-closure models of NTD, which highlight the fact that CNS malformations are of hetergeneitic nature. No Mendelian pattern of inheritance has been reported. Association with single gene defects, enhanced recurrence risk among siblings, and a higher frequency in twins than in singletons indicate the presence of a strong genetic contribution to the etiology of NTD. Non-availability of families with a significant number of NTD cases makes research into genetic causation of NTD difficult. Case reports and epidemiologic studies have implicated a number of chemicals, widely differing therapeutic drugs, environmental contaminants, pollutants, infectious agents, and solvents. Maternal hyperthermia, use of valproate by epileptic women during pregnancy, deficiency and excess of certain nutrients and chronic maternal diseases (e.g. diabetes mellitus) are reported to cause a manifold increase in the incidence of NTD. A host of suspected teratogens are also available in the literature. The UK and Hungarian studies showed that periconceptional supplementation of women with folate (FA) reduces significantly both the first occurrence and recurrence of NTD in the offspring. This led to mandatory periconceptional FA supplementation in a number of countries. Encouraged by the results of clinical studies, numerous laboratory investigations focused on the genes involved in the FA, vitamin B12 and homocysteine metabolism during neural tube development. As of today no clinical or experimental study has provided unequivocal evidence for a definitive role for any of these genes in the causation of NTD suggesting that a multitude of genes, growth factors and receptors interact in controlling neural tube development by yet unknown mechanisms. Future studies must address issues of gene-gene, gene-nutrient and gene-environment interactions in the pathogenesis of NTD.     

Prevention of neural tube defects with folic acid: The Chinese experience

Neural tube defects(NTDs) are a group of congenital malformations of the central nervous system that are caused by the closure failure of the embryonic neural tube by the 28 th day of conception. Anencephaly and spina bifida are the two major subtypes. Fetuses with anencephaly are often stillborn or electively aborted due to prenatal diagnosis, or they die shortly after birth. Most infants with spina bifida are live-born and, with proper surgical treatment, can survive into adulthood. However, these children often have life-long physical disabilities. China has one of the highest prevalence of NTDs in the world. Inadequate dietary folate intake is believed to be the main cause of the cluster. Unlike many other countries that use staple fortification with folic acid as the public health strategy to prevent NTDs, the Chinese government provides all women who have a rural household registration and who plan to become pregnant with folic acid supplements, free of charge, through a nation-wide program started in 2009. Two to three years after the initiation of the program, the folic acid supplementation rate increased to 85% in the areas of the highest NTD prevalence. The mean plasma folate level of women during early and mid-pregnancy doubled the level before the program was introduced. However, most women began taking folic acid supplements when they knew that they were pregnant. This is too late for the protection of the embryonic neural tube. In a postprogram survey of the women who reported folic acid supplementation, less than a quarter of the women began taking supplements prior to pregnancy, indicating that the remaining three quarters of the fetuses remained unprotected during the time of neural tube formation. Therefore, staple food fortification with folic acid should be considered as a priority in the prevention of NTDs.     

Use of local neural tube defect registers to interpret national trends.

To conduct a number of studies into the prevalence of neural tube defects (NTD) in the area covered by the Oxford Record Linkage Study (ORLS), multiple sources were used to build a local register of cases occurring in Oxfordshire and West Berkshire between 1968-1990. One source of potential cases--namely, termination and congenital malformation monitoring data available for the locality from the Office of Population Censuses and Surveys (OPCS) data--were kept separate. Comparison of the local cases recorded by OPCS and those known to the register from 1974-1990, using the method of capture-recapture, suggested that national data are only about two thirds complete, but that this underreporting is likely to be reasonably consistent from year to year. OPCS data can therefore be used to study NTD trends if not absolute risks. The local register seemed, by the same yardstick, to be very complete and is being used in a variety of studies of the occurrence of NTD. Survival to one year in this area, over the period 1968-1990, has only improved in the recent past, if at all. Most NTD pregnancies now end in termination rather than birth, and there has been a true decline in the occurrence of NTDs, and likewise the different subtypes.     

Folic acid fortification prevents neural tube defects and may also reduce cancer risks

The prevalence of neural tube defect (NTD)‐affected pregnancies ranges between 0.4 and 2/1000 pregnancies in EU. NTDs result in severe malformations and sometimes miscarriages. Children born with NTD suffer for the rest of their life of disability and chronic healthcare issues, and many women therefore choose termination of pregnancy if NTD is diagnosed prenatally. Women planning for pregnancy are recommended to eat 400 μg folic acid/d, whereas average figures across Europe indicate intakes of ～250 μg/d for women of fertile age, a gap that could be bridged by implementation of folic acid fortification. The results of mandatory folic acid fortifications introduced in USA and Canada are a decrease between 25 and 45% of NTD pregnancies. Conclusion: Evidence‐based NTD prophylaxis is now practised in more than 60 countries worldwide. EU countries worry over possible cancer risks, but ignore a wealth of studies reporting decreasing cancer risks with folate intakes at recommended levels. Currently, there are indications of a U‐shaped relationship, that is, higher cancer risks at low folate intakes (<150 μg/day) and highly elevated folate intakes (>1 mg/day), respectively. However neither the global World Cancer Research review nor EU’s European Food Safety Authority report present data on increased cancer risk at physiological folate intake levels. Therefore, EU should act to implement folic acid fortification as NTD prophylaxis as soon as possible.     

Neurulation in the human embryo revisited

ABSTRACT It used to be widely accepted that neural tube closure in the human initiates at the level of the future neck and proceeds both cranially and caudally like zip fastener closing. This continuous closure model was recently challenged, and observation of human embryos at the neurulation stage revealed that the closure of the human neural tube initiates at multiple sites. Multi-site closure of the neural tube has been observed in many other animal species, but the initiation sites and the process of neural tube closure are variable among species. Therefore we should be careful when extrapolating the data of normal and abnormal neurulation in laboratory animals to the human. Recent studies in mouse genetics and developmental biology have shown that neural tube defects are quite heterogeneous both etiologically and pathogenetically. Gene mutations responsible for human neural tube defects are largely unknown, but molecular studies of human cases of neural tube defects and their comparison with the mouse genome data should provide a molecular basis for human neural tube defects.     

Amelioration of sodium valproate-induced neural tube defects in mouse fetuses by maternal folic acid supplementation during gestation

Infants of epileptic women treated with valproic acid (VPA) during pregnancy have a higher risk of developing spina bifida than those of the general population. VPA induces exencephaly in experimental animal embryos. But the pathogenetic mechanism remains rather elusive. Antiepileptic drugs (AED) in general accentuate pregnancy-imposed fall in maternal folate levels. Periconceptional folic acid supplementation is reported to protect embryos from developing neural tube defects (NTD). Conflicting results have been reported by experimental studies that attempted to alleviate VPA-induced NTD by folic acid. Our objectives were to determine the critical developmental stages and an effective dose of folic acid for the prevention of VPA-induced exencephaly in mouse fetuses. A single teratogenic dose of 400 mg/kg of VPA was administered to TO mice on gestation day (GD) 7 or 8. It was followed by (1) a single dose of 12 mg/kg of FA (folinic acid) or (2) 3 doses of FA 4 mg/kg each. In experiment (3), FA (4 mg/kg) was administered thrice daily starting on GD 5 and continued through GD 10. These animals received VPA on GD 7 or 8. VPA and B12 concentrations were determined by radioimmunoassay. The single heavy dose of FA had no rescue effect on NTD. Three divided doses of FA on GD 7 and continuous dosing of FA from GD 5 through GD 10 substantially reduced the VPA-induced exencephaly in the fetuses. In the later experiments, the neural folds elevated faster than the non-supplemented group. VPA considerably reduced maternal plasma folate and B12 concentrations. The heavy dose of FA only moderately improved vitamin levels. Three divided doses of FA elevated the vitamin levels slightly better but it was the prolonged dosing of FA that was associated with sustained elevation of plasma levels higher than the control levels and acceleration of neural tube closure thus accounting for the pronounced protection against VPA-induced NTD development. These data suggest that plasma levels of FA and B12 have to be kept substantially elevated and maintained high throughout organogenesis period to protect embryos against VPA-induced NTD in this mouse model.     

Folate and neural tube defects: The role of supplements and food fortification

Periconceptional folic acid significantly reduces the risk of neural tube defects. It is difficult to achieve optimal levels of folate by diet alone, even with fortification of flour, especially because flour consumption in Canada is slightly decreasing. Intermittent concerns have been raised concerning possible deleterious effects of folate supplementation, including the masking of symptoms of vitamin B₁₂ deficiency and an association with cancer, especially colorectal cancer. Both concerns have been disproved. The Canadian Paediatric Society endorses the following steps to enhance folate intake in women of child-bearing age: encouraging the consumption of folate-rich foods such as leafy vegetables, increasing the level of folate food fortification, taking a supplement containing folate and B₁₂, and providing free folate supplementation to disadvantaged women of child-bearing age. These recommendations are consistent with those of the Society of Obstetricians and Gynaecologists of Canada.     

Neural tube defects : Prevention by folic acid and other vitamins

Folic acid has been demonstrated in clinical trials to reduce significantly the recurrence (and probably occurrence) of neural tube defects (NTD). In the U.K., there has been no decline in prevalence of NTD since the publication of the findings with folic acid. This article examines a series of questions relating to the action of folic acid, with emphasis on the use of mouse models as a source of experimental information which cannot easily be obtained by direct study of humans. Several mouse genetic NTD models exhibit sensitivity to prevention by folic acid, whereas other mice which develop morphologically similar NTD are resistant. Folic acid normalises neurulation in the sensitive mouse strains, providing evidence for a direct effect on the developing embryo, not on the pregnant female. Mouse studies do not support the proposed action of folic acid in encouraging thein utero demise of affected fetuses (i.e. terathanasia). Polymorphic variants of several folate-related enzymes have been shown to influence risk of NTD in humans and an inherited abnormality of folate metabolism has been demonstrated in one mouse NTD model. However, the biochemical basis of the action of folic acid in preventing NTD remains to be determined in detail. NTD in one folate-resistant mouse strain can be prevented by myoinositol, bothin utero andin vitro, raising the possibility of a therapeutic role also in humans. Gene-gene interactions seem likely to underlie the majority of NTD, suggesting that poly-therapy involving folic acid and other agents, such as myo-inositol, may prove more effective in preventing NTD than folic acid treatment alone.     

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

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.     

Segmental costovertebral malformations: association with neural tube defects. Report of 3 cases and review of the literature.

Patients with spondylocostal dysostosis (SCD) have vertebral abnormalities and numerical or structural rib anomalies that produce thoracic asymmetry. Rib anomalies and dysmorphism are the typical features that differentiate this syndrome from spondylothoracic dysostosis (STD). Jarcho-Levin syndrome is a severe form with involvement of the whole vertebral column. Other associated findings such as congenital heart defects, abdominal wall malformations, genitourinary malformations and upper limb anomalies may be found; in addition, neural tube defects (NTDs) have been associated with this malformation. SCD is transmitted both in a recessive form and as a dominant defect. We report on 3 children with SCD; 2 also had NTDs. All of them were studied with X-rays and spinal magnetic resonance (MR), and over the same period they underwent multidisciplinary clinical functional evaluation. One of our cases with NTD also presented polythelia, which has not previously been described in patients with SCD. The common association of segmental costovertebral malformations with NTDs could be related to an early gastrulation genomic defect, or one after gastrulation, when there are two independent somitic columns. The latter sometimes progresses and then involves primary and secondary neurulation. Also, the association of SCD with NTDs could be related to the interaction of different genes, resulting in this complex phenotype. Therefore, additional genetical and embryological studies are necessary to provide evidence of an etiological link between SCD and NTD.     

Valproic acid-induced congenital malformations: Clinical and experimental observations

ABSTRACT With a large number of epileptic women being in the childbearing age group, complications of pregnancy in epileptic patients are of concern. Epileptic women are treated with antiepileptic drugs (AED) whether they are pregnant or not. Contrary to prevailing opinion, recent data suggest that epilepsy per se contributes significantly to birth defects possibly because of the same genetic susceptibility that predisposes to epilepsy. Many of these defects closely resemble those attributed to exposure to AED. The syndromes attributed to various AED also considerably overlap with each other. Valproic acid (VPA) induces several minor and major malformations. The relative risk for spina bifida in VPA exposed pregnancies is nearly 20 times higher than that for the general population and about 10 times higher than that attributed to other anticonvulsants. Fetuses of experimental animals treated with VPA during pregnancy exhibit exencephaly unlike the human offspring in whom VPA induces spina bifida. The cranial and spinal malformations observed in humans and laboratory animals indicate that VPA has a preferentially deleterious effect on the neural crest. Several AEDs including VPA tend to lower maternal plasma folate levels. In view of the beneficial effects of periconceptional folate supplementation in prevention of neural tube defects (NTD), future research should be directed at the role of folate in the possible alleviation of VPA-induced NTD. It is also necessary to continue prospective studies to monitor the old and new AED prescribed and to evaluate the role of interactions between drugs used in combinations.     

Fetal evaluation of spine dysraphism

Spinal dysraphism or neural tube defects (NTD) encompass a heterogeneous group of congenital spinal anomalies that result from the defective closure of the neural tube early in gestation with anomalous development of the caudal cell mass. Advances in ultrasound and MRI have dramatically improved the diagnosis and therapy of spinal dysraphism and caudal spinal anomalies both prenatally and postnatally. Advances in prenatal US including high frequency linear transducers and three dimensional imaging can provide detailed information concerning spinal anomalies. MR imaging is a complementary tool that can further elucidate spine abnormalities as well as associated central nervous system and non-CNS anomalies. Recent studies have suggested that 3-D CT can help further assess fetal spine anomalies in the third trimester. With the advent of fetal therapy including surgery, accurate prenatal diagnosis of open and closed spinal dysraphism becomes critical in appropriate counselling and perinatal management.     

Neural tube defects in Turkey: prevalence, distribution and risk factors

The aim of the study was to determine the prevalence rate and risk factors relevant to neural tube defects (NTDs) in Turkey. All livebirths and stillbirths recorded at the university hospitals throughout Turkey between July 1993-June 1994 were evaluated with respect to congenital anomalies. For each birth, information was recorded about the child, the mother, the pregnancy and risk factors. A total of 66 cases with a NTD were recorded in 21,907 births. Prevalence rate of NTDs was 30.1 per 10,000 births. Of these 66 cases, 29 (43.9%) were male and 37 (56.1%) female. Female/male ratio was 1.27. The ratio of spina bifida/anencephaly is 1.20 for Turkey. Maternal illiteracy, maternal advanced age and residence in northern or eastern regions of Turkey are shown to be risk factors for having a baby with a NTD. The prevalence rate of NTDs is very high for Turkey. Geographical distribution of NTDs in this country confirms a relationship between the socioeconomic status and environmental factors for the development of a NTD. The results of this study point to the importance establishing a health policy to prevent neural tube defects in Turkey.     

Serum zinc levels in newborns with neural tube defects

Neural tube defects (NTD) comprise of a group of congenital malformations that include spina bifida, anencephaly and encephalocele. Reports have implicated zinc deficiency as one of the causative factors of NTDs. We compared the serum zinc level of 23 newborns having neural tube defects with 35 healthy controls by spectrophotometery during 2003-2004. Zinc deficiency was documented in 43.5% of the cases and 8.6% of the controls (P = 0.002). Multivariate logistic regression analysis revealed a significant association between the presence of NTDs and zinc deficiency (OR = 8.2, 95% Cl: 1.9-34.7).     

神经管缺陷畸形的蛋白质学研究进展

神经管缺陷(neural tube defects,NTD)是在胚胎发育过程中,神经管闭合不全所引起的一组缺陷,是环境因素和遗传因素共同作用的结果。目前已发现的与 NTD 相关的蛋白质标志物主要有血清甲胎蛋白、羊水甲胎蛋白、羊水胶质纤维酸性蛋白和 S100蛋白。该文对 NTD 相关的蛋白质标志物的研究进展进行综述。     

Evaluation of the MTHFR C677T allele and the MTHFR gene locus in a German spina bifida population

A number of recent studies have demonstrated that the occurrence and recurrence risk of neural tube defects (NTD) is reduced by folic acid supplementation before and during pregnancy. Epidemiological studies have shown low plasma folate and raised plasma homocysteine in women with spina bifida aperta (SB) children suggesting an abnormal folate metabolism. The 5,10-methylenetetrahydrofolate reductase (MTHFR) variant C677T, resulting in a decreased activity of the enzyme, has been associated with the development of NTD. Several studies demonstrated that homozygosity for the C677T mutation occurs at a higher frequency in patients with SB phenotype than in control individuals. The SB risk is strongest if both the mother and her child have the mutation in the homozygous state. In the present study we compared the frequency of the C- and T-alleles in healthy German individuals (n=153) with German SB patients (n=137). Our study groups reveal no significant difference in C/T-allele frequencies and genotype distributions. A family based association study, the transmission disequilibrium test, confirms the absence of an association between T-allele and SB. In 9 of 40 families we were able to exclude linkage to the MTHFR locus (1p36.3) employing different inheritance models. Conclusion Our data show no evidence for an association between the C677T mutation and the occurrence of the SB phenotype. Therefore we cannot support the hypothesis that the MTHFR variant does account for a significant genetic predisposition to the SB phenotype in the studied German patients. Received: 11 June 1997 / Accepted in revised form: 3 November 1997     

Craniosynostosis associated with neural tube defects: is there a causal association?

The majority of primary craniosynostosis cases are sporadic. Very few articles in the literature have described cases of primary craniosynostosis associated with neural tube defects (NTDs). This co-occurrence has been seen by most authors as just a coincidence. The authors report a clinical series of 4 patients of primary craniosynostosis associated with NTDs treated at their center. Among these 4 cases, 2 had lumbosacral myelomeningocele, 1 frontoethmoidal encephalocele and 1 had occipital encephalocele. Although the co-occurrence of craniosynostosis and NTD is said to be rare, there seems to exist a justified underlying explanation for the same. The NTD causes a decrease in intracranial pressure due to egress of cerebrospinal fluid in the malformed sac that results in a deficient cerebral impulse for cranial growth that might stimulate premature sutural fusion. Thus, all patients with NTDs should be thoroughly evaluated for this association and for possible surgical management.     

Morphological analysis of neural tube defects: Chlorambucil-induced exencephaly in mice

Abstract: Exencephaly has been induced in mouse embryos by chlorambucil (CA), a cytotoxic agent. To understand the course of development of this malformation, open neural tube defects in CA-treated mice were examined using light and scanning electron microscopes (SEM). CA was given to the pregnant mice on day 7.4 of gestation. Embryos were removed and fixed on gestational days 9.3–9.4, 9.7–9.8 and 10.4, and compared to control embryos from untreated mice. By gestational day 9.4, all control embryos had closed neural tubes, except for the posterior neuropores, and well developed brain vesicles. By contrast, in the experimental embryos the frequencies of open neural tube were 26/33 (78.8%), 32/ 40 (80.0%) and 23/66 (34.8%) on each day examined, respectively. Open neural tube defects were classified into six patterns according to the location and magnitude of the open area. The patterns of open neural tube on day 9.7–9.8 were diverse; however, in almost all cases on day 10.4 the open neural tube appeared in a region from the caudal forebrain to the rostral hindbrain. It was evident that an unusual pattern of closure of the neural tube was involved in forming the cranial neural tube. The present study shows that failure of closure of the cranial neural tube in the CA-treated mouse embryos can be defined as a primary neural tube defect (NTD), which can be, in part, repaired by unusual closure of the neural tube.
At high magnifications of SEM, the neuroectodermal surfaces of the 9.0-day affected embryos often had a number of slender processes projecting from the neuroepithelial cells. "Ruffles" and "blebs" at the lateral edges of the neural folds were observed in both control and affected embryos.     

Structural birth defects associated with omphalocele and gastroschisis, Hawaii, 1986–2001

ABSTRACT   There is limited information on the specific structural birth defects associated with the abdominal wall defects (AWD) omphalocele and gastroschisis, particularly which defects occur with the AWD at greater than expected rates (rates among all infants and fetuses with birth defects other than the AWD). Using data from a population-based birth defects registry in Hawaii, this study calculated the rates for 48 specific structural birth defects among the AWD and compared these rates to the expected rates. There were 60 cases of omphalocele, 96 cases of gastroschisis, and 12 161 infants and fetuses with structural birth defects excluding the AWD among deliveries during 1986–2001. For omphalocele, higher than expected rates were found for 23 (47.9%) of the defects. These involved defects of a variety of organ systems. For gastroschisis, higher than expected rates were found for 8 (16.7%) of the defects, mainly neural tube defects (NTD) and specific defects of the orofacial and gastrointestinal system and the genital and urinary system. Both omphalocele and gastroschisis had elevated rates for NTD, intestinal atresia/stenosis, malrotation of intestines, obstructive genitourinary defects and limb reduction deformities. Certain specific structural birth defects occurred more often than expected with the AWD. The associated birth defects tended to vary between omphalocele and gastroschisis, although there were a few similarities. Due to the small number of cases, further research involving larger amounts of data are warranted.