Autoantibodies to folate receptor during pregnancy and neural tube defect risk

Dolutegravir induces FOLR1 expression during brain organoid development

During the first month of pregnancy, the brain and spinal cord are formed through a process called neurulation. However, this process can be altered by low serum levels of folic acid, environmental factors, or genetic predispositions. In 2018, a surveillance study in Botswana, a country with a high incidence of human immunodeficiency virus (HIV) and lacking mandatory food folate fortification programs, found that newborns whose mothers were taking dolutegravir (DTG) during the first trimester of pregnancy had an increased risk of neural tube defects (NTDs). As a result, the World Health Organization and the U.S. Food and Drug Administration have issued guidelines emphasizing the potential risks associated with the use of DTG-based antiretroviral therapies during pregnancy. To elucidate the potential mechanisms underlying the DTG-induced NTDs, we sought to assess the potential neurotoxicity of DTG in stem cell-derived brain organoids. The gene expression of brain organoids developed in the presence of DTG was analyzed by RNA sequencing, Optical Coherence Tomography (OCT), Optical Coherence Elastography (OCE), and Brillouin microscopy. The sequencing data shows that DTG induces the expression of the folate receptor (FOLR1) and modifies the expression of genes required for neurogenesis. The Brillouin frequency shift observed at the surface of DTG-exposed brain organoids indicates an increase in superficial tissue stiffness. In contrast, reverberant OCE measurements indicate decreased organoid volumes and internal stiffness.

Dolutegravir-induced neural tube defects in mice are folate responsive

OBJECTIVES

In 2018, the Botswana Tsepamo Study reported a nine-fold increased risk of neural tube defects in infants whose mothers were treated with dolutegravir (DTG) from the time of conception. As maternal folate supplementation and status is a well known modifier of neural tube defect (NTD) risk, we sought to evaluate birth outcomes in mice fed normal and low folic acid diets treated with DTG during pregnancy.

DESIGN

DTG was evaluated for developmental toxicity using pregnant mice fed normal or low folic acid diet.

METHODS

CD-1 mice were provided diet with normal (3 mg/kg) or low (0.3 mg/kg) folic acid. They were treated with water, a human therapeutic-equivalent dose, or supratherapeutic dose of DTG from mouse embryonic day E6.5 to E12.5. Pregnant dams were sacrificed at term (E18.5) and fetuses were inspected for gross, internal, and skeletal defects.

RESULTS

Fetuses with exencephaly, an NTD, were present in both therapeutic human equivalent and supratherapeutic exposures in dams fed low folic acid diet. Cleft palates were also found under both folate conditions.

CONCLUSIONS

Recommended dietary folic acid levels during mouse pregnancy ameliorate developmental defects that arise from DTG exposure. Since low folate status in mice exposed to DTG increases the risk for NTDs, it is possible that DTG exposures in people living with HIV with low folate status during pregnancy may explain, at least in part, the elevated NTD risk signal observed in Botswana. Based on these results, future studies should consider folate status as a modifier for DTG-associated NTD risk.

Folate receptor alpha autoantibodies in the serum of patients with relapsing-remitting multiple sclerosis (RRMS)

OBJECTIVE

Multiple sclerosis (MS) is a potentially progressive, autoimmune neurologic disorder of the central nervous system (CNS), resulting from an autoimmune attack on central nervous system white matter. Folate deficiencies are linked to DNA instability and breakdown of phospholipid membranes and thus might affect myelin integrity. Folic acid exerts its effects through its receptors (FRs). Folate receptor alpha autoantibodies (FRAA) can block folate transport to the brain. Due to important role of folate in the pathogenesis of MS, in this project we aimed to study FRAA serum levels in patients with relapsing remitting multiple sclerosis (RRMS).

METHODS

Fifty-four patients with RRMS and 58 healthy individuals were enrolled in this study. Serum samples were collected from all participants and folate receptor alpha autoantibody (FRAA) serum concentration was measured by Enzyme-linked immunosorbent assay (ELISA).

RESULTS

The results showed that FRAA serum levels in patients with RRMS is 67.20 ± 19.79 ng/ml as compared to controls which was 37.32 ± 13.26 ng/ml. Significant increase in folate receptor autoantibody serum concentration was seen in patients with RRMS when compared to control group (P = 0.007). The results showed that a high concentration of folate receptor autoantibody is associated with RRMS. We have also found that 85.18% (46/54) of patients with RRMS were positive for serum FRAA, whereas the prevalence in controls was only 46.55% (27/58).

CONCLUSIONS

It is concluded that serum FRAA are more prevalent in RRMS patients than controls. The findings also suggest that FRAA might be involved in the pathophysiology of RRMS.

Recent Advances in Folates and Autoantibodies against Folate Receptors in Early Pregnancy and Miscarriage

Though firstly identified in cerebral folate deficiency, autoantibodies against folate receptors (FRAbs) have been implicated in pregnancy complications such as miscarriage; however, the underlying mechanism needs to be further elaborated. FRAbs can be produced via sensitization mediated by folate-binding protein as well as gene mutation, aberrant modulation, or degradation of folate receptors (FRs). FRAbs may interfere with folate internalization and metabolism through blocking or binding with FRs. Interestingly, different types of FRs are expressed on trophoblast cells, decidual epithelium or stroma, and macrophages at the maternal-fetal interface, implying FRAbs may be involved in the critical events necessary for a successful pregnancy. Thus, we propose that FRAbs may disturb pregnancy establishment and maintenance by modulating trophoblastic biofunctions, placental development, decidualization, and decidua homeostasis as well as the functions of FOLR2+ macrophages. In light of these findings, FRAbs may be a critical factor in pathological pregnancy, and deserve careful consideration in therapies involving folic acid supplementation for pregnancy complications.

CIC missense variants contribute to susceptibility for spina bifida

Neural tube defects (NTDs) are congenital malformations resulting from abnormal embryonic development of the brain, spine, or spinal column. The genetic etiology of human NTDs remains poorly understood despite intensive investigation. CIC, homolog of the Capicua transcription repressor, has been reported to interact with ataxin-1 (ATXN1) and participate in the pathogenesis of spinocerebellar ataxia type 1. Our previous study demonstrated that CIC loss of function (LoF) variants contributed to the cerebral folate deficiency syndrome by downregulating folate receptor 1 (FOLR1) expression. Given the importance of folate transport in neural tube formation, we hypothesized that CIC variants could contribute to increased risk for NTDs by depressing embryonic folate concentrations. In this study, we examined CIC variants from whole-genome sequencing (WGS) data of 140 isolated spina bifida cases and identified eight missense variants of CIC gene. We tested the pathogenicity of the observed variants through multiple in vitro experiments. We determined that CIC variants decreased the FOLR1 protein level and planar cell polarity (PCP) pathway signaling in a human cell line (HeLa). In a murine cell line (NIH3T3), CIC loss of function variants downregulated PCP signaling. Taken together, this study provides evidence supporting CIC as a risk gene for human NTD.

Pathogenesis of neural tube defects: The regulation and disruption of cellular processes underlying neural tube closure

Neural tube closure (NTC) is crucial for proper development of the brain and spinal cord and requires precise morphogenesis from a sheet of cells to an intact three-dimensional structure. NTC is dependent on successful regulation of hundreds of genes, a myriad of signaling pathways, concentration gradients, and is influenced by epigenetic and environmental cues. Failure of NTC is termed a neural tube defect (NTD) and is a leading class of congenital defects in the United States and worldwide. Though NTDs are all defined as incomplete closure of the neural tube, the pathogenesis of an NTD determines the type, severity, positioning, and accompanying phenotypes. In this review, we survey pathogenesis of NTDs relating to disruption of cellular processes arising from genetic mutations, altered epigenetic regulation, and environmental influences by micronutrients and maternal condition. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Genetics/Genomics/Epigenetics Neurological Diseases > Stem Cells and Development.

Folate Receptor Alpha is Decreased in Pregnancy Affected with Fetal Neural Tube Defect: A Case Control Study

BACKGROUND

Neural tube defect (NTD) is a multifactorial disorder. Decrease transfer of folate to the developing embryo is one of the etiologies. It could be due to decrease folate receptors resulting in NTD in fetus.

OBJECTIVE

To analyze serum folate receptor alpha (FOLR1) concentration in women having fetus with NTD and compare it with women having normal fetus during and after pregnancy.

MATERIAL AND METHODS

This was a prospective case control study conducted in a tertiary care hospital. Pregnant women with detected isolated NTD in fetus were enrolled as cases and equal number of matched pregnant women without any fetal congenital malformation were recruited as controls. Serum FOLR1 levels were analyzed in cases and controls during pregnancy and 6 weeks after delivery.

RESULTS

Mean serum FOLR1 concentration during pregnancy was 70.5 pg/mL (range: 23.8-98.5 pg/mL) and 103.9 pg/mL (range: 70-110 pg/mL) in cases and controls, respectively. Serum level of FOLR1 was 448.9 pg/mL (range: 133.5-475) and 414.5 pg/mL (range: 269.7-412.5) in cases and controls at 6 weeks postpartum, respectively. There was statistically significant difference (P < 0.001) between cases and control during pregnancy but not in postpartum (P = 0.092). There was significant increase in level of FOLR1 in both cases and control at 6 weeks postpartum as compared to antenatal period.

CONCLUSIONS

Maternal serum FOLR1 is significantly reduced in pregnancy with fetal NTD as compared to normal pregnancy. The level is significantly increased in postpartum period in both groups. FOLR1 level being similar in both groups in postpartum indicates that it is not influenced by the history of fetal NTD.

Maternal folic acid and multivitamin supplementation: International clinical evidence with considerations for the prevention of folate-sensitive birth defects

More evidence is available for maternal intake, absorption, distribution, tissue specific concentrations, and pregnancy outcomes with folic acid (fortification/supplementation) during preconception - first trimester. This Quality Improvement prevention review used expert guidelines/opinions, systematic reviews, randomized control trials/controlled clinical trials, and observational case control/case series studies, published in English, from 1990 to August 2021. Optimization for an oral maternal folic acid supplementation is difficult because it relies on folic acid dose, type of folate supplement, bio-availability of the folate from foods, timing of supplementation initiation, maternal metabolism/genetic factors, and many other factors. There is continued use of high dose pre-food fortification 'RCT evidenced-based' folic acid supplementation for NTD recurrence pregnancy prevention. Innovation requires preconception and pregnancy use of 'carbon one nutrient' supplements (folic acid, vitamin B12, B6, choline), using the appropriate evidence, need to be considered. The consideration and adoption of directed personalized approaches for maternal complex risk could use serum folate testing for supplementation dosing choice. Routine daily folic acid dosing for low-risk women should consider a multivitamin with 0.4 mg of folic acid starting 3 months prior to conception until completion of breastfeeding. Routine folic acid dosing or preconception measurement of maternal serum folate (after 4-6 weeks of folate supplementation) could be considered for maternal complex risk group with genetic/medical/surgical co-morbidities. These new approaches for folic acid oral supplementation are required to optimize benefit (decreasing folate sensitive congenital anomalies; childhood morbidity) and minimizing potential maternal and childhood risk.

Folate Receptor Alpha Autoantibodies in Autism Spectrum Disorders: Diagnosis, Treatment and Prevention

Folate deficiency and folate receptor autoimmune disorder are major contributors to infertility, pregnancy related complications and abnormal fetal development including structural and functional abnormalities of the brain. Food fortification and prenatal folic acid supplementation has reduced the incidence of neural tube defect (NTD) pregnancies but is unlikely to prevent pregnancy-related complications in the presence of folate receptor autoantibodies (FRAb). In pregnancy, these autoantibodies can block folate transport to the fetus and in young children, folate transport to the brain. These antibodies are prevalent in neural tube defect pregnancies and in developmental disorders such as cerebral folate deficiency (CFD) syndrome and autism spectrum disorder (ASD). In the latter conditions, folinic acid treatment has shown clinical improvement in some of the core ASD deficits. Early testing for folate receptor autoantibodies and intervention is likely to result in a positive outcome. This review discusses the first identification of FRAb in women with a history of neural tube defect pregnancy and FRAb’s association with sub-fertility and preterm birth. Autoantibodies against folate receptor alpha (FRα) are present in about 70% of the children with a diagnosis of ASD, and a significant number of these children respond to oral folinic acid with overall improvements in speech, language and social interaction. The diagnosis of folate receptor autoimmune disorder by measuring autoantibodies against FRα in the serum provides a marker with the potential for treatment and perhaps preventing the pathologic consequences of folate receptor autoimmune disorder.

Chylomicronemia from GPIHBP1 autoantibodies

Some cases of chylomicronemia are caused by autoantibodies against glycosylphosphatidylinositol-anchored HDL binding protein 1 (GPIHBP1), an endothelial cell protein that shuttles LPL to the capillary lumen. GPIHBP1 autoantibodies prevent binding and transport of LPL by GPIHBP1, thereby disrupting the lipolytic processing of triglyceride-rich lipoproteins. Here, we review the "GPIHBP1 autoantibody syndrome" and summarize clinical and laboratory findings in 22 patients. All patients had GPIHBP1 autoantibodies and chylomicronemia, but we did not find a correlation between triglyceride levels and autoantibody levels. Many of the patients had a history of pancreatitis, and most had clinical and/or serological evidence of autoimmune disease. IgA autoantibodies were present in all patients, and IgG4 autoantibodies were present in 19 of 22 patients. Patients with GPIHBP1 autoantibodies had low plasma LPL levels, consistent with impaired delivery of LPL into capillaries. Plasma levels of GPIHBP1, measured with a monoclonal antibody-based ELISA, were very low in 17 patients, reflecting the inability of the ELISA to detect GPIHBP1 in the presence of autoantibodies (immunoassay interference). However, GPIHBP1 levels were very high in five patients, indicating little capacity of their autoantibodies to interfere with the ELISA. Recently, several GPIHBP1 autoantibody syndrome patients were treated successfully with rituximab, resulting in the disappearance of GPIHBP1 autoantibodies and normalization of both plasma triglyceride and LPL levels. The GPIHBP1 autoantibody syndrome should be considered in any patient with newly acquired and unexplained chylomicronemia.

CIC de novo loss of function variants contribute to cerebral folate deficiency by downregulating FOLR1 expression

Background Cerebral folate deficiency (CFD) syndrome is characterised by a low concentration of 5-methyltetrahydrofolate in cerebrospinal fluid, while folate levels in plasma and red blood cells are in the low normal range. Mutations in several folate pathway genes, including FOLR1 (folate receptor alpha, FRα), DHFR (dihydrofolate reductase) and PCFT (proton coupled folate transporter) have been previously identified in patients with CFD.

Methods In an effort to identify causal mutations for CFD, we performed whole exome sequencing analysis on eight CFD trios and identified eight de novo mutations in seven trios.

Results Notably, we found a de novo stop gain mutation in the capicua (CIC) gene. Using 48 sporadic CFD samples as a validation cohort, we identified three additional rare variants in CIC that are putatively deleterious mutations. Functional analysis indicates that CIC binds to an octameric sequence in the promoter regions of folate transport genes: FOLR1, PCFT and reduced folate carrier (Slc19A1; RFC1). The CIC nonsense variant (p.R353X) downregulated FOLR1 expression in HeLa cells as well as in the induced pluripotent stem cell (iPSCs) derived from the original CFD proband. Folate binding assay demonstrated that the p.R353X variant decreased cellular binding of folic acid in cells.

Conclusion This study indicates that CIC loss of function variants can contribute to the genetic aetiology of CFD through regulating FOLR1 expression. Our study described the first mutations in a non-folate pathway gene that can contribute to the aetiology of CFD.

Mouse Models of Neural Tube Defects

During embryonic development, the central nervous system forms as the neural plate and then rolls into a tube in a complex morphogenetic process known as neurulation. Neural tube defects (NTDs) occur when neurulation fails and are among the most common structural birth defects in humans. The frequency of NTDs varies greatly anywhere from 0.5 to 10 in 1000 live births, depending on the genetic background of the population, as well as a variety of environmental factors. The prognosis varies depending on the size and placement of the lesion and ranges from death to severe or moderate disability, and some NTDs are asymptomatic. This chapter reviews how mouse models have contributed to the elucidation of the genetic, molecular, and cellular basis of neural tube closure, as well as to our understanding of the causes and prevention of this devastating birth defect.

Emerging biomarkers in autism spectrum disorder: a systematic review

Autism spectrum disorder (ASD) affects approximately 2% of children in the United States (US) yet its etiology is unclear and effective treatments are lacking. Therapeutic interventions are most effective if started early in life, yet diagnosis often remains delayed, partly because the diagnosis of ASD is based on identifying abnormal behaviors that may not emerge until the disorder is well established. Biomarkers that identify children at risk during the pre-symptomatic period, assist with early diagnosis, confirm behavioral observations, stratify patients into subgroups, and predict therapeutic response would be a great advance. Here we underwent a systematic review of the literature on ASD to identify promising biomarkers and rated the biomarkers in regards to a Level of Evidence and Grade of Recommendation using the Oxford Centre for Evidence-Based Medicine scale. Biomarkers identified by our review included physiological biomarkers that identify neuroimmune and metabolic abnormalities, neurological biomarkers including abnormalities in brain structure, function and neurophysiology, subtle behavioral biomarkers including atypical development of visual attention, genetic biomarkers and gastrointestinal biomarkers. Biomarkers of ASD may be found prior to birth and after diagnosis and some may predict response to specific treatments. Many promising biomarkers have been developed for ASD. However, many biomarkers are preliminary and need to be validated and their role in the diagnosis and treatment of ASD needs to be defined. It is likely that biomarkers will need to be combined to be effective to identify ASD early and guide treatment.

The antagonism of folate receptor by dolutegravir: developmental toxicity reduction by supplemental folic acid

OBJECTIVE

Maternal folate (vitamin B9) status is the largest known modifier of neural tube defect risk, so we evaluated folate-related mechanisms of action for dolutegravir (DTG) developmental toxicity.

DESIGN

Folate receptor 1 (FOLR1) was examined as a target for DTG developmental toxicity using protein and cellular interaction studies and an animal model.

METHODS

FOLR1 competitive binding studies were used to test DTG for FOLR1 antagonism. Human placenta cell line studies were used to test interactions with DTG, folate, and cations. Zebrafish were selected as an animal model to examine DTG-induced developmental toxicity and rescue strategies.

RESULTS

FOLR1 binding studies indicate DTG is a noncompetitive FOLR1 antagonist at therapeutic concentrations. In-vitro testing indicates calcium (2 mmol/l) increases FOLR1-folate interactions and alters DTG-FOLR1-folate interactions and cytotoxicity. DTG does not inhibit downstream folate metabolism by dihydrofolate reductase. Early embryonic exposure to DTG is developmentally toxic in zebrafish, and supplemental folic acid can mitigate DTG developmental toxicity.

CONCLUSION

Folates and FOLR1 are established modifiers of risk for neural tube defects, and binding data indicates DTG is a partial antagonist of FOLR1. Supplemental folate can ameliorate increased developmental toxicity due to DTG in zebrafish. The results from these studies are expected to inform and guide future animal models and clinical studies of DTG-based antiretroviral therapy in women of childbearing age.

Does L-Methylfolate Supplement Methylphenidate Pharmacotherapy in Attention-Deficit/Hyperactivity Disorder?: Evidence of Lack of Benefit From a Double-Blind, Placebo-Controlled, Randomized Clinical Trial

PURPOSE/BACKGROUND

Interventions for attention-deficit/hyperactivity disorder (ADHD) may be inadequate for some patients. There is evidence that supplementation with L-methylfolate augments antidepressant agent effects and thus might also augment ADHD treatment effects by a common catecholaminergic mechanism.

METHODS

Forty-four adults with Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition diagnosis of ADHD participated in a randomized, double-blind, placebo-controlled, 12-week trial of 15 mg of L-methylfolate in combination with osmotic-release oral system methylphenidate. Osmotic-release oral system methylphenidate was dose optimized over the first 6 weeks. We evaluated the effects on ADHD symptoms, self-report on the Behavior Rating Inventory of Executive Function of executive function, methylphenidate dosing, neuropsychological test measures, the Adult ADHD Self-report scale, emotional dysregulation, social adjustment, and work productivity, as well as moderating effects of body mass index, autoantibodies to folate receptors, and select genetic polymorphisms.

RESULTS

L-Methylfolate was well tolerated, with no significant effect over placebo except improvement from abnormal measures on the mean adaptive dimension of the ASR scale (χ = 4.36, P = 0.04). Methylphenidate dosing was significantly higher in individuals on L-methylfolate over time (χ = 7.35, P = 0.007). Exploratory analyses suggested that variation in a guanosine triphosphate cyclohydrolase gene predicted association with higher doses of methylphenidate (P < 0.001).

CONCLUSIONS

L-Methylfolate was associated with no change in efficacy on measures relevant to neuropsychiatric function in adults with ADHD, other than suggestion of reduced efficacy of methylphenidate. Further investigation would be required to confirm this effect and its mechanism and the genotype prediction of effects on dosing.

Farletuzumab, a monoclonal antibody directed against folate receptor alpha, shows no evidence of teratogenicity in cynomolgus monkeys

Farletuzumab is a humanized monoclonal antibody targeting human folate receptor alpha, which is being developed as an anti-cancer drug. A non-human primate reproductive study was conducted to evaluate whether it could cause any embryonic or fetal abnormalities. Farletuzumab was administered intravenously to pregnant cynomolgus monkeys (n = 16/group) at doses of 0 or 67.5 mg/kg once weekly during gestation day (GD) 20 through 97. C-section was performed on GD100 ± 2, and fetuses were evaluated for morphologic (external, visceral and skeletal) effects. No farletuzumab-related changes were observed in maternal animals or fetuses, which are supported by the fact that farletuzumab has no effects on cellular uptake of folate. These data support the potential use of farletuzumab for oncologic indications during pregnancy.

Gene variants in the folate pathway are associated with increased levels of folate receptor autoantibodies

BACKGROUND

Folate receptors (FRs) facilitate embryonic uptake of folates and are important for proper early embryonic development. There is accumulating evidence that blocking FR autoantibodies contribute to developmental diseases. However, genetic factors associated with the expression of FR autoantibodies remain unknown.

OBJECTIVE

We investigated the effects of genetic polymorphisms in folate pathway genes on FR autoantibody titers in women.

METHODS

We recruited 302 pregnant women in China. The FR antigen-down immunoassay was used to measure levels of FR autoantibodies including human immunoglobulin G (IgG) and immunoglobulin M (IgM) in maternal plasma. Genotypes were identified by matrix-assisted laser desorption/ionization time of flight mass spectrometry and polymerase chain reaction methods. General linear model was used to analyze the effects of genetic variants on FR autoantibody levels.

RESULTS

Significant associations were observed between genotypic variations and levels of FR autoantibodies. Plasma levels of FR autoantibodies in women with the TT genotype at MTHFR rs1801133 were significantly higher than those of women with the CC genotype (IgG: β = 0.62, 95% CI 0.21-1.04; IgM: β = 0.42, 95% CI 0.12-0.72). For DNMT3A rs7560488, the level of FR autoantibody IgG significantly increased in the TT genotype compared with CC genotype (β = 0.90, 95% CI 0.20-1.59). For MTHFD2 rs828903, genotype GG was associated with elevated levels of FR autoantibody IgM compared to the AA genotype (β = 0.60, 95% CI 0.10-1.10). No association was detected between genetic variants of the DHFR gene with FR autoantibodies levels.

CONCLUSION

Genetic variations in MTHFR, DNMT3A, and MTHFD2 genes were associated with elevated plasma levels of FR autoantibodies.

Folate receptors and neural tube closure

Neural tube defects (NTD) are among the most common human congenital malformations, affecting 0.5-8.0/1000 of live births. Human clinical trials have shown that periconceptional folate supplementation significantly decreases the occurrence of NTD in offspring. However, the mechanism by which folate acts on NTD remains largely unknown. Folate receptor (Folr) is one of the three membrane proteins that mediate cellular uptake of folates. Recent studies suggest that mouse Folr1 (formerly referred to as Fbp1) is essential for neural tube closure. Therefore, we examined spatial and temporal expression patterns of Folr1 in developing mouse embryos, showing a close association between Folr1 and anterior neural tube closure. Transient transgenic analysis was performed using lacZ as a reporter; we identified a 1.1-kb enhancer that directs lacZ expression in the neural tube and optic vesicle in a manner that is similar to endogenous Folr1. The 1.1-kb enhancer sequences were highly conserved between humans and mice, suggesting that human FOLR1 is associated with anterior neural tube closure in humans. Several experimental studies in mice and human epidemiological and genetics studies have suggested that folate receptor abnormalities are involved in a portion of human NTDs, although the solo defect of FOLR1 did not cause NTD.

Prevention of behavioral deficits in rats exposed to folate receptor antibodies: implication in autism

Folate receptor alpha (FRα) autoantibodies have been associated with fetal abnormalities and cerebral folate deficiency-related developmental disorders. Over 70% of the children with autism spectrum disorders (ASD) are positive for these autoantibodies and high-dose folinic acid is beneficial in treating these children. Here we show that antibodies (Abs) to the rat FRα administered during gestation produce communication, learning and cognitive deficits in a rat model that can be prevented by folinic acid and dexamethasone. FRα Ab can trigger inflammation as well as block folate transport to the fetus and to the developing brain to produce the functional deficits. In humans, exposure to FRα autoantibodies during fetal development and infancy could contribute to brain dysfunction such as that seen in ASD and other developmental disorders. Identifying women positive for the autoantibody and treating them with high-dose folinic acid along with other interventions to lower the autoantibody titer are effective strategies that may be considered to reduce the risk of having a child with developmental deficits.

Levels of folate receptor autoantibodies in maternal and cord blood and risk of neural tube defects in a Chinese population

BACKGROUND

After years of periconceptional folic acid supplementation, the prevalence of neural tube defects (NTDs) remains stable following the remarkable reduction observed immediately after the fortification practice. There is accumulating evidence that folate receptor (FR) autoimmunity may play a role in the etiology of folate-sensitive NTDs.

METHODS

From 2011 to 2013, 118 NTD cases and 242 healthy controls were recruited from a population-based birth defects surveillance system in Northern China. Enzyme-linked immunosorbent assay was used to measure FR autoantibodies in maternal and cord blood. Logistic regression models were used to estimate the odds ratios (OR) and 95% confidence intervals (95% CI).

RESULTS

Plasma FR autoantibodies levels were significantly elevated in mothers of infants with NTDs compared with mothers of healthy controls. Using the lowest tertile as the referent group, 2.20-fold (95% CI, 0.71-6.80) and 5.53-fold increased odds (95% CI, 1.90-16.08) of NTDs were observed for the second and third tertile of immunoglobulin G (IgG), respectively, and the odds of NTDs for each successive tertile of IgM was 0.98 (95% CI, 0.35-2.75) and 3.49 (95% CI, 1.45-8.39), respectively. A dose-response relationship was found between FR autoantibodies levels and risk of NTDs (P < 0.001 for IgG, P = 0.002 for IgM). The same pattern was observed in both subtypes of spina bifida and anencephaly. No significant difference in levels of cord blood FR autoantibodies was observed.

CONCLUSION

Higher levels of FR autoimmunity in maternal plasma are associated with elevated risk of NTDs in a dose-response manner. Birth Defects Research (Part A) 106:685-695, 2016. © 2016 Wiley Periodicals, Inc.

Exposure to Folate Receptor Alpha Antibodies during Gestation and Weaning Leads to Severe Behavioral Deficits in Rats: A Pilot Study

The central nervous system continues to develop during gestation and after birth, and folate is an essential nutrient in this process. Folate deficiency and folate receptor alpha autoantibodies (FRα-AuAb) have been associated with pregnancy-related complications and neurodevelopmental disorders. In this pilot study, we investigated the effect of exposure to FRα antibodies (Ab) during gestation (GST), the pre-weaning (PRW), and the post weaning (POW) periods on learning and behavior in adulthood in a rat model. In the open field test and novel object recognition task, which examine locomotor activity and anxiety-like behavior, deficits in rats exposed to Ab during gestation and pre-weaning (GST+PRW) included more time spent in the periphery or corner areas, less time in the central area, frequent self-grooming akin to stereotypy, and longer time to explore a novel object compared to a control group; these are all indicative of increased levels of anxiety. In the place avoidance tasks that assess learning and spatial memory formation, only 30% of GST+PRW rats were able to learn the passive place avoidance task. None of these rats learned the active place avoidance task indicating severe learning deficits and cognitive impairment. Similar but less severe deficits were observed in rats exposed to Ab during GST alone or only during the PRW period, suggesting the extreme sensitivity of the fetal as well as the neonatal rat brain to the deleterious effects of exposure to Ab during this period. Behavioral deficits were not seen in rats exposed to antibody post weaning. These observations have implications in the pathology of FRα-AuAb associated with neural tube defect pregnancy, preterm birth and neurodevelopmental disorders including autism.

Autoantibodies against homocysteinylated protein in a mouse model of folate deficiency-induced neural tube defects

BACKGROUND

Periconceptional supplementation with folic acid results in a significant reduction in the incidence of neural tube defects (NTDs). Nonetheless, NTDs remain a leading cause of perinatal morbidity and mortality worldwide, and the mechanism(s) by which folate exerts its protective effects are unknown. Homocysteine is an amino acid that accumulates under conditions of folate-deficiency, and is suggested as a risk factor for NTDs. One proposed mechanism of homocysteine toxicity is its accumulation into proteins in a process termed homocysteinylation.

METHODS & RESULTS

Herein, we used a folate-deficient diet in pregnant mice to demonstrate that there is: (i) a significant inverse correlation between maternal serum folate levels and serum homocysteine; (ii) a significant positive correlation between serum homocysteine levels and titers of autoantibodies against homocysteinylated protein; and (iii) a significant increase in congenital malformations and NTDs in mice deficient in serum folate. Furthermore, in mice administered the folate-deplete diet before conception, supplementation with folic acid during the gestational period completely rescued the embryos from congenital defects, and resulted in homocysteinylated protein titers at term that are comparable to that of mice administered a folate-replete diet throughout both the pre- and postconception period. These results demonstrate that a low-folate diet that induces NTDs also increases protein homocysteinylation and the subsequent generation of autoantibodies against homocysteinylated proteins.

CONCLUSION

These data support the hypotheses that homocysteinylation results in neo-self antigen formation under conditions of maternal folate deficiency, and that this process is reversible with folic acid supplementation.

Folate receptor autoantibodies in pregnancy related complications

BACKGROUND

Folate receptor autoantibodies in women have been associated with neural tube pregnancy and in children with cerebral folate deficiency syndrome and autism. These autoantibodies have been implicated in blocking folate transport to the fetus and to the brain in infants.

METHODS

We report a woman with multiple pregnancy related complications who was diagnosed with autoantibodies to the folate receptor alpha.

RESULTS

A treatment strategy with folate supplementation and reducing the antibody titer proved effective in normal pregnancy outcome.

CONCLUSION

This long-term follow up of a subject with folate receptor autoantibodies is a first report of its kind and describes treatment strategy to prevent pregnancy related complications due to folate receptor autoantibodies.

The application of a chemical determination of N-homocysteinylation levels in developing mouse embryos: implication for folate responsive birth defects

Elevated homocysteine levels have long been associated with various disease states, including cardiovascular disease and birth defects, including neural tube defects (NTDs). One hypothesis regarding the strong correlation between these various disorders and high levels of homocysteine is that a reactive form of this small molecule can attach to mammalian proteins in a phenomenon known as homocysteinylation. These posttranslational modifications may become antigenic or may even directly disrupt certain protein function. It remains to be determined whether dietary influences that can cause globally increased levels of circulating homocysteine confer negative effects maternally, or may otherwise negatively and materially impact the metabolic balance in developing embryos. Herein we present the application of a chemical method of determination of N-homocysteinylation to a set of neural tube closure stage mouse embryos and their mothers. We explore the uses of this newly described technique to investigate levels of maternal and embryonic N-homocysteinylation using dietary manipulations of one-carbon metabolism with two known folate-responsive NTD mouse models. The data presented reveal that although diet appeared to have significant effects on the maternal metabolic status, those effects did not directly correlate to the embryonic folate or N-homocysteinylation status. Our studies indicate that maternal diet and embryonic genotype most significantly affected the embryonic developmental outcome.

Folate deficiency in rat pups during weaning causes learning and memory deficits

Folate is essential for fetal development, and its deficiency during gestation causes behavioural deficits in the offspring. The present study investigated its influence during weaning on brain function in the pups of rats that were put on a folate-deficient (FD) diet on postnatal day (PND) 1. Systemic folate deficiency in pups on the FD diet (n 15) was evident from the dramatically lower hepatic folate concentrations (median 23·7, range 8·1–48·4 ng/mg protein) and higher homocysteine concentrations (median 27·7, range 14·7–45·5 pmol/mg protein), respectively, compared with those of pups on the normal diet (ND; n 9) (median 114·5, range 64·5–158·5 ng/mg protein and median 15·5, range 11·6–18·9 pmol/mg protein) on PND 23. Brain folate concentrations although low were similar in pups on the FD diet (median 10·5, range 5·5–24·5 ng/mg protein) and ND (median 11·1, range 7·1–24·2 ng/mg protein). There was a high accumulation of homocysteine in the brain of FD pups, mostly in the hippocampus (median 58·1, range 40·8–99·7 pmol/mg protein) and cerebellum (median 69·1, range 50·8–126·6 pmol/mg protein), indicating metabolic folate deficiency despite normal brain folate concentrations. Developmental deficits or autistic traits were more frequent in the FD group than in the ND group and repetitive self-grooming occurred, on average, three times (range 1–8) v. once (range 0–3) during 5 min, respectively. Long-term memory or spatial learning and set-shifting deficits affected 12 to 62 % of rats in the FD group compared with none in the ND group. Post-weaning folic acid supplementation did not correct these deficits. These observations indicate that folate deficiency during weaning affects postnatal development even when gestational folate supply is normal.

Brief report novel mechanism for valproate-induced teratogenicity

BACKGROUND

Valproic acid (VPA) is a commonly prescribed drug for those affected by epilepsy and bipolar disorders. VPA has a well known teratogenic potential, causing a variety of birth defects including neural tube defects (NTDs) and other congenital malformations, when women are treated with this medication during pregnancy. Unfortunately, the mechanism by which VPA is teratogenic remains unknown, although a range of potential mechanisms including histone deacetylase inhibition and folate antagonism have been proposed. The latter is of considerable importance, as clinicians need to know if additional folate supplements can prevent VPA-induced defects.

METHODS

We herein approach this question experimentally, using enzyme-linked immunosorbent assay assays and cell culture modeling, to demonstrate that VPA serves as a noncompetitive inhibitor of the high affinity folate receptors.

RESULTS

Binding affinities experimentally determined through enzyme-linked immunosorbent assay assays indicate that VPA serves as a noncompetitive substrate that can lessen the ability of the three primary folate forms to bind to the high affinity folate receptors. Tests in HEK293T cells indicate that the membrane-bound folate receptors of VPA treated cells bind significantly lower amounts of folic acid than do untreated cells.

CONCLUSION

If these data translate to the overall transport and subsequent bioavailability of folates, noncompetitive inhibition of the folate receptors by VPA may serve to lower the bioavailable folates in VPA treated mothers. This represents a novel mechanism by which in utero VPA exposure could be disrupting developmental processes by noncompetitively binding to the folate receptors during embryogenesis, thus inducing the wide range of defects seen in babies born to VPA treated mothers.

Neural tube defects, folate, and immune modulation

Periconceptional supplementation with folic acid has led to a significant worldwide reduction in the incidence of neural tube defects (NTDs). However, despite increasing awareness of the benefits of folic acid supplementation and the implementation of food fortification programs in many countries, NTDs continue to be a leading cause of perinatal morbidity and mortality worldwide. Furthermore, there exists a significant subgroup of women who appear to be resistant to the protective effects of folic acid supplementation. The following review addresses emerging clinical and experimental evidence for a role of the immune system in the etiopathogenesis of NTDs, with the aim of developing novel preventative strategies to further reduce the incidence of NTD-affected pregnancies. In particular, recent studies demonstrating novel roles and interactions between innate immune factors such as the complement cascade, neurulation, and folate metabolism are explored.

LRP2 mediates folate uptake in the developing neural tube

The low-density lipoprotein (LDL) receptor-related protein 2 (LRP2) is a multifunctional cell-surface receptor expressed in the embryonic neuroepithelium. Loss of LRP2 in the developing murine central nervous system (CNS) causes impaired closure of the rostral neural tube at embryonic stage (E) 9.0. Similar neural tube defects (NTDs) have previously been attributed to impaired folate metabolism in mice. We therefore asked whether LRP2 might be required for the delivery of folate to neuroepithelial cells during neurulation. Uptake assays in whole-embryo cultures showed that LRP2-deficient neuroepithelial cells are unable to mediate the uptake of folate bound to soluble folate receptor 1 (sFOLR1). Consequently, folate concentrations are significantly reduced in Lrp2(-/-) embryos compared with control littermates. Moreover, the folic-acid-dependent gene Alx3 is significantly downregulated in Lrp2 mutants. In conclusion, we show that LRP2 is essential for cellular folate uptake in the developing neural tube, a crucial step for proper neural tube closure.

Lack of association between folate receptor autoantibodies and conotruncal congenital heart defects

Conotruncal cardiac defects are partially prevented by maternal folic acid supplementation. However, the biochemical mechanism is unknown. Maternal autoantibodies to folate receptors, previously associated with increased risk for neural tube defects, also may account for this effect. This study aimed to examine the titers of folate receptor-blocking autoantibodies in mothers of children with conotruncal congenital heart defects and to compare them with those in the general population. Serum samples were obtained from 22 women whose pregnancies were complicated by conotruncal congenital heart malformations. Groups of samples were analyzed for autoantibodies against [(3)H] folic acid-labeled folate receptors, quantitative amounts of immunoglobulin G (IgG) and IgM autoantibodies to the folate receptor, and for ability to block-bind folic acid to receptors. No elevated levels of antibodies binding to [(3)H] folic acid-labeled folate receptors were found. No difference was found in antifolate receptor alpha-IgG or IgM median levels between cases (261 vs. 240 μg/mL) and control subjects (773 vs. 924 μg/mL). There was no increased blocking of folic acid binding between cases [0.69 ng/mL; 95 % confidence interval (CI), 0.006-0.01] and control subjects (0.69 ng/mL; 95 % CI, 0.003-0.013). Although epidemiologic evidence suggests that periconceptual folic acid may prevent many conotruncal congenital heart defects, the current study suggests that this effect is unlikely to be explained by the presence of maternal autoantibodies to folate receptor. These data suggest that a strategy of screening women for such autoantibodies will not identify a high-risk group of women to target for supplemental folic acid to prevent congenital heart defects.

Maternal and fetal antibrain antibodies in development and disease

Recent evidence has emerged indicating that the maternal immune response can have a substantial deleterious impact on prenatal development (Croen et al., [2008]: Biol Psychiatry 64:583-588). The maternal immune response is largely sequestered from the fetus. Maternal antibodies, specifically immunoglobulin G (IgG), are passed to the fetus to provide passive immunity throughout much of pregnancy. However, both protective and pathogenic autoantibodies have equal access to the fetus (Goines and Van de Water [2010]: Curr Opin Neurol 23:111-117). If the mother has an underlying autoimmune disease or has reactivity to fetal antigens, autoantibodies produced before or during pregnancy can target tissues in the developing fetus. One such tissue is the fetal brain. The blood brainbarrier (BBB) is developing during the fetal period allowing maternal antibodies to have direct access to the brain during gestation (Diamond et al. [2009]: Nat Rev Immunol; Braunschweig et al. [2011]; Neurotoxicology 29:226-231). It has been proposed that brain injury by circulating brain-specific maternal autoantibodies might underlie multiple congenital, developmental disorders (Lee et al. [2009]: Nat Med 15:91-96). In this review, we will discuss the current state of research in the area of maternal autoantibodies and the development of autism.

Impact of folic acid fortification of flour on neural tube defects: a systematic review

Objective

To review the impact of folic acid fortification of flour on the prevalence of neural tube defects (NTD).

Design

Systematic review of the literature on MEDLINE via PubMed, Scopus, OvidSP and LILACS (Latin American and Caribbean Health Sciences Literature) reporting the impact of folic acid fortification of flour on the prevalence of NTD in 2000–2011. Focusing on Santiago of Chile's birth defects registry (1999–2009) and the monitoring of flour fortification, we analysed the prevalence (NTD cases/10 000 births) pre and post flour fortification and the percentile distribution of folic acid content in flour (2005–2009). We explored the potential association between median folic acid in flour (mg/kg) and the prevalence of NTD.

Setting

Chile, Argentina, Brazil, Canada, Costa Rica, Iran, Jordan, South Africa and the USA.

Subjects

Live births and stillbirths.

Results

Twenty-seven studies that met inclusion criteria were evaluated. Costa Rica showed a significant reduction in NTD (∼60 %). Prevalence in Chile decreased from 18·6 to 7·3/10 000 births from 1999 to 2007 and showed a slight increase to 8·5 in 2008–2009, possibly due to changes in fortification limits. When we related the prevalence of NTD with levels of flour fortification, the lowest prevalence was observed at a folic acid level of 1·5 mg/kg.

Conclusions

Fortification of flour with folic acid has had a major impact on NTD in all countries where this has been reported. Chile showed a 55 % reduction in NTD prevalence between 1999 and 2009. There is a need to constantly monitor the levels of flour fortification to maximize benefits and prevent the potential risk of folic acid excess, moreover to be vigilant for any new adverse effects associated with excess.

Association between inhibited binding of folic acid to folate receptor alpha in maternal serum and folate-related birth defects in Norway

BACKGROUND

Folic acid intake during pregnancy can reduce the risk of neural tube defects (NTDs) and perhaps also oral facial clefts. Maternal autoantibodies to folate receptors can impair folic acid binding. We explored the relationship of these birth defects to inhibition of folic acid binding to folate receptor α (FRα), as well as possible effects of parental demographics or prenatal exposures.

METHODS

We conducted a nested case-control study within the Norwegian Mother and Child Cohort Study. The study included mothers of children with an NTD (n = 11), cleft lip with or without cleft palate (CL/P, n= 72), or cleft palate only (CPO, n= 27), and randomly selected mothers of controls (n = 221). The inhibition of folic acid binding to FRα was measured in maternal plasma collected around 17 weeks of gestation. On the basis of prior literature, the maternal age, gravidity, education, smoking, periconception folic acid supplement use and milk consumption were considered as potential confounding factors.

RESULTS

There was an increased risk of NTDs with increased binding inhibition [adjusted odds ratio (aOR) = 1.4, 95% confidence interval (CI) 1.0-1.8]. There was no increased risk of oral facial clefts from inhibited folic acid binding to FRα (CL/P aOR = 0.7, 95% CI 0.6-1.0; CPO aOR = 1.1, 95% CI 0.8-1.4). No association was seen between smoking, folate supplementation or other cofactors and inhibition of folic acid binding to FRα.

CONCLUSIONS

Inhibition of folic acid binding to FRα in maternal plasma collected during pregnancy was associated with increased risk of NTDs but not oral facial clefts.

A mouse model of hereditary folate malabsorption: deletion of the PCFT gene leads to systemic folate deficiency

The human proton coupled folate transporter (PCFT) is involved in low pH-dependent intestinal folate transport. In this report, we describe a new murine model of the hereditary folate malabsorption syndrome that we developed through targeted disruption of the first 3 coding exons of the murine homolog of the PCFT gene. By 4 weeks of age, PCFT-deficient (PCFT(-/-)) mice developed severe macrocytic normochromic anemia and pancytopenia. Immature erythroblasts accumulated in the bone marrow and spleen of PCFT(-/-) mice and failed to differentiate further, showing an increased rate of apoptosis in intermediate erythroblasts and reduced release of reticulocytes. In response to the inefficient hematologic development, the serum of the PCFT(-/-) animals contained elevated concentrations of erythropoietin, soluble transferrin receptor (sCD71), and thrombopoietin. In vivo folate uptake experiments demonstrated a systemic folate deficiency caused by disruption of PCFT-mediated intestinal folate uptake, thus confirming in vivo a critical and nonredundant role of the PCFT protein in intestinal folate transport and erythropoiesis. The PCFT-deficient mouse serves as a model for the hereditary folate malabsorption syndrome and is the most accurate animal model of folate deficiency anemia described to date that closely captures the spectrum of pathology typical of this disease.

Folate pathway and nonsyndromic cleft lip and palate

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate (NSCLP) is a common complex birth defect. Periconceptional supplementation with folic acid, a key component in DNA synthesis and cell division, has reduced the birth prevalence of neural tube defects and may similarly reduce the birth prevalence of other complex birth defects including NSCLP. Past studies investigating the role of two common methylenetetrahydrofolate reductase (MTHFR) single-nucleotide polymorphisms (SNPs), C677T (rs1801133) and A1298C (rs1801131), in NSCLP have produced conflicting results. Most studies of folate pathway genes have been limited in scope, as few genes/SNPs have been interrogated. Here, we asked whether variations in a more comprehensive group of folate pathway genes were associated with NSCLP, and were there detectable interactions between these genes and environmental exposures?

METHODS

Fourteen folate metabolism-related genes were interrogated using 89 SNPs in multiplex and simplex non-Hispanic white and Hispanic NSCLP families.

RESULTS

Evidence for a risk association between NSCLP and SNPs in NOS3 and TYMS was detected in the non-Hispanic white group, whereas associations with MTR, BHMT2, MTHFS, and SLC19A1 were detected in the Hispanic group. Evidence for over-transmission of haplotypes and gene interactions in the methionine arm was detected.

CONCLUSIONS

These results suggest that perturbations of the genes in the folate pathway may contribute to NSCLP. There was evidence for an interaction between several SNPs and maternal smoking, and for one SNP with gender of the offspring. These results provide support for other studies that suggest that high maternal homocysteine levels may contribute to NSCLP and should be further investigated.

Gene-environment interactions, folate metabolism and the embryonic nervous system

Formation of brain and spinal cord requires the successful closure of neural ectoderm into an embryonic neural tube. Defects in this process result in anencephaly or spina bifida, which together constitute a leading cause of mortality and morbidity in children, affecting all ethnic and socioeconomic groups. The subject of intensive research for decades, neural tube defects (NTDs), are understood to arise from complex interactions of genes and environmental conditions, though systems-level details are still elusive. Despite the variety of underlying causes, a single intervention, folic acid supplementation given in the first gestational month, can measurably reduce the occurrence of NTDs in a population. Evidence for and the scope of gene-environment interactions in the genesis of NTDs is discussed. A systems-based approach is now possible toward studies of genetic and environmental influences underlying NTDs that will enable the assessment of individual risk and personalized optimization of prevention.

Folic acid and orofacial clefts: a review of the evidence

Orofacial clefts are common and burdensome birth defects with a complex genetic and environmental etiology. The contribution of nutritional factors and supplements to the etiology of orofacial clefts has long been theorized and studied. Multiple studies have evaluated the role of folic acid in the occurrence and recurrence of orofacial clefts, using observational and non-randomized interventional designs. While preventive effects of folic acid on orofacial clefts are commonly reported, the evidence remains generally inconsistent. This paper reviews the findings of the main studies of the effects of folic acid on orofacial clefts, summarizes study limitations, and discusses research needs with a focus on studying the effects of high dosage folic acid on the recurrence of oral clefts using a randomized clinical trial design. The role of folic acid in the prevention of neural tube defects is also briefly summarized and discussed as a reference model for orofacial clefts.

Autoantibodies to folate receptor alpha during early pregnancy and risk of oral clefts in Denmark

The objective of this study was to determine whether IgG and IgM autoantibodies to folate receptor alpha (FRalpha) in pregnant women are associated with an increased risk of oral cleft-affected offspring. A case-control study nested in the prospective Danish National Birth Cohort (100,418 pregnancies, enrolled during 1997-2003) was done. Hundred eighty-five children were born with an oral cleft. Maternal serum from their mothers (cases) was compared with maternal serum from 779 randomly selected mothers of nonmalformed children (controls). We found that the average level of FRalpha IgG autoantibodies did not differ significantly among cases and controls (p = 0.71). Slightly higher levels of FRalpha IgM autoantibodies were found among controls compared with cases. This was, however, not statistically significant (p = 0.06), except for mothers of children with isolated cleft lip (p = 0.04). Blocking of folate binding to FR was similar among cases and controls (p = 0.54). The results did not change when stratifying into the cleft subgroups, nor when only isolated oral cleft cases were considered. In conclusion, high maternal autoantibody levels and blocking of folate binding to FRalpha in maternal serum during pregnancy are not associated with an increased risk of oral clefts in the offspring in this population-based cohort.

Importance of gene-environment interactions in the etiology of selected birth defects

It is generally understood that both genetic and environmental factors contribute to the highly complex etiology of structural birth defects, including neural tube defects, oral clefts and congenital heart defects, by disrupting highly regulated embryonic developmental processes. The intrauterine environment of the developing embryo/fetus is determined by maternal factors such as health/disease status, lifestyle, medication, exposure to environmental teratogens, as well as the maternal genotype. Certain genetic characteristics of the embryo/fetus also predispose it to developmental abnormalities. Epidemiologic and animal studies conducted over the last few decades have suggested that the interplay between genes and environmental factors underlies the etiological heterogeneity of these defects. It is now widely believed that the study of gene-environment interactions will lead to better understanding of the biological mechanisms and pathological processes that contribute to the development of complex birth defects. It is only through such an understanding that more efficient measures will be developed to prevent these severe, costly and often deadly defects. In this review, we attempt to summarize the complex clinical and experimental literature on current hypotheses of interactions between several select environmental factors and those genetic pathways in which they are most likely to have significant modifying effects. These include maternal folate nutritional status, maternal diabetes/obesity-related conditions, and maternal exposure to selected medications and environmental contaminants. Our goal is to highlight the potential gene-environment interactions affecting early embryogenesis that deserve comprehensive study.

Lack of association between folate-receptor autoantibodies and neural-tube defects

BACKGROUND

A previous report described the presence of autoantibodies against folate receptors in 75% of serum samples from women with a history of pregnancy complicated by a neural-tube defect, as compared with 10% of controls. We sought to confirm this finding in an Irish population, which traditionally has had a high prevalence of neural-tube defects.

METHODS

We performed two studies. Study 1 consisted of analysis of stored frozen blood samples collected from 1993 through 1994 from 103 mothers with a history of pregnancy complicated by a neural-tube defect (case mothers), 103 mothers with a history of pregnancy but no complication by a neural-tube defect (matched with regard to number of pregnancies and sampling dates), 58 women who had never been pregnant, and 36 men. Study 2, conducted to confirm that the storage of samples did not influence the folate-receptor autoantibodies, included fresh samples from 37 case mothers, 22 control mothers, 10 women who had never been pregnant, and 9 men. All samples were assayed for blocking and binding autoantibodies against folate receptors.

RESULTS

In Study 1, blocking autoantibodies were found in 17% of case mothers, as compared with 13% of control mothers (odds ratio, 1.54; 95% confidence interval [CI], 0.70 to 3.39), and binding autoantibodies in 29%, as compared with 32%, respectively (odds ratio, 0.82; 95% CI, 0.44 to 1.50). Study 2 showed similar results, indicating that sample degradation was unlikely.

CONCLUSIONS

The presence and titer of maternal folate-receptor autoantibodies were not significantly associated with a neural-tube defect-affected pregnancy in this Irish population.

High milk consumers have an increased risk of folate receptor blocking autoantibody production but this does not affect folate status in Spanish men and women

Folate receptor (FR)-blocking autoantibodies (FR-autoantibodies) have been reported in women with neural tube defect-affected pregnancies and subfertility and in children with progressive neurodevelopment disorders. We investigated their prevalence and association with folate status and milk intake in adults unexposed to folic acid fortification. A cross-sectional study of a randomly selected representative sample of a Spanish population (aged 18-75 y) stratified by age and gender was performed. Plasma and red cell folate, plasma cobalamin, fasting plasma total homocysteine (tHcy) concentration, methylenetetrahydrofolate reductase C677T polymorphism, and FR-autoantibody titer were determined in blood samples from 787 fasting participants. Lifestyle data were collected and milk intake estimated from a 3-d dietary record. FR-autoantibody prevalence was 7.2% [0.30 +/- 0.27 nmol (mean +/- SD) FR blocked/L], equally affecting men and women of all ages. Plasma and red cell folate and tHcy did not differ between carriers and noncarriers of FR-autoantibodies. Milk intake was higher in carriers (225 +/- 199 g/d) than in noncarriers (199 +/- 147 g/d) (P < 0.01). The risk of having FR-autoantibodies increased progressively with increasing quintile of milk intake and was significant in the highest quintile (> or =307 g/d) compared with the lowest (< or =67 g/d) [odds ratio (OR), 2.41 [95% CI: 1.02, 5.69]; P < 0.05; linear trend, P = 0.02]. We concluded that FR-autoantibodies occur in men and women of all ages and do not affect indicators of folate status such as plasma and red cell folate and tHcy. Higher milk intake is associated with increased risk of having FR-autoantibodies.