The role of Vitamin B12 and genetic risk factors in the etiology of neural tube defects: A systematic review

Neural tube defects (NTDs) are birth defects that arise during embryogenesis when normal neural tube closure fails to occur. According to the World Health Organization, NTDs are detected annually in approximately 300,000 neonates worldwide. The exact etiology of NTDs remains complex and poorly understood. It is generally agreed that most NTD cases are of multifactorial origin, having a combination of multiple genes and a number of environmental risk factors. The role of folic acid, vitamin B12 deficiency, genetics and other risk factors, in the etiology of NTDs, has also been extensively studied. This knowledge synthesis brings together different types of evidence to update the role of vitamin B12 deficiency, genetics and other risk factors, in the etiology of NTDs. Following a PubMed search and screening for relevant articles, we included 40 studies in our review (30 case-control studies, 3 cross-sectional studies, 5 cohort studies, and 2 case reports). The available data showed that vitamin B12 levels were decreased in mothers and infants in NTD groups compared with control groups. Holo-transcobalamin, the active form of vitamin B12, was also found in lower levels in mothers with NTD-affected infants. Several studies reported elevated homocysteine levels in mothers and infants in NTD groups. Additionally, numerous studies reported links between genetic variants and increased NTD risk. These genes include GIF, LRP2, CUBN, TCb1R, MTHFR, and others. Several maternal factors have also been linked with significant NTD risk such as BMI, maternal diet, air pollutants, low maternal age, and many others. The majority of studies on NTDs have focused on the role of folic acid, hence there is a need for well-designed studies on the role of other risk factors like vitamin B12 deficiency in the etiology of NTDs.

Folate fortification and supplementation in prevention of folate-sensitive neural tube defects: a systematic review of policy

OBJECTIVE

Neural tube defects (NTDs) are common congenital neurological defects, resulting in mortality, morbidity, and impaired quality of life for patients and caregivers. While public health interventions that increase folate consumption among women who are or plan to become pregnant are shown to reduce folate-sensitive NTDs, public health policy reflecting the scientific evidence lags behind. The authors aimed to identify the types of policies applied, associated outcomes, and impact of folate fortification and supplementation on NTDs worldwide. By identifying effective legislation, the authors aim to focus advocacy efforts to more broadly effect change, reducing the burden of NTDs in neurosurgery.

METHODS

A systematic review was conducted exploring folate fortification and supplementation policies using the PubMed and Scopus databases. Titles and abstracts from articles identified were read and selected for full-text review. Studies meeting inclusion criteria were reviewed in full and analyzed for study design, aim, population, interventions, and outcomes.

RESULTS

Of 1637 resultant articles, 54 were included. Mandatory folate fortification was effective at reducing folate-sensitive NTDs. Mandatory fortification also decreased hospitalization rates and deaths after discharge and increased 1st-year survival for infants with NTDs. Recommended folate supplementation also resulted in decreased NTDs; however, issues with compliance and adherence were a concern and impacted effectiveness. Folate fortification and/or supplementation resulted in decreased NTD prevalence, although more change was attributed to fortification. Dual policies may hold the most promise. Furthermore, reductions in NTDs were associated with significant cost savings over time.

CONCLUSIONS

Both mandatory folate fortification and recommended supplementation policies were found to effectively decrease folate-sensitive NTD rates when applied. A comprehensive approach incorporating mandatory folate fortification, appropriate folate supplementation, and improved infrastructure and access to prenatal care may lead to decreased NTDs worldwide. This approach should be context-specific, emphasize education, and account for regional access to healthcare and social determinants of health. With wide implications for NTDs, associated health outcomes, quality of life of patients and caregivers, and economic impacts, policy changes can drastically improve global NTD outcomes. As caretakers of children with NTDs, the authors as neurosurgeons advocate for a comprehensive policy, the engagement of stakeholders, and a broader global impact.

Prevalence of open neural tube defects and risk factors related to isolated anencephaly and spina bifida in live births from the "Dr. Juan I. Menchaca" Civil Hospital of Guadalajara (Jalisco, Mexico)

We determine the prevalence and trends of open neural tube defects (ONTDs) during 1991 to 2019 at the "Dr. Juan I. Menchaca" Civil Hospital of Guadalajara (Mexico). Also, details of potential risks were obtained in 662 newborns, including those 143 patients with anencephaly and open spina bifida (OSB) classified as isolated (cases) and 519 controls. Data were analyzed using multivariable logistic regression. Among 267 201 live births during the study period, 336 were born with ONTDs, yielding an overall prevalence of 12.6 per 10 000. After folic acid (FA)-related programs began in Mexico (2003-2019), only OSB showed a decline of 20.6%. For anencephaly, associated risks included relatives with neural tube defects (NTDs) (adjusted odds ratio [aOR]: 67.9, 95% confidence interval [95% CI]: 11.3-409.8), pre-pregnancy body mass index (BMI) ≥25 kg/m² (aOR: 2.6, 95% CI: 1.1-6.0), insufficient gestational weight gain (aOR: 3.0, 95% CI: 1.3-7.1), parity ≥4 (aOR: 3.2, 95% CI: 1.3-7.7), and exposure to analgesic/antipyretic drugs (aOR: 9.0; 95% CI: 2.5-33.0). For OSB, associated risks included consanguinity (aOR: 14.0, 95% CI: 3.5-55.9), relatives with NTDs (aOR: 22.4, 95% CI: 4.5-112.9), BMI ≥25 kg/m² (aOR: 2.5, 95% CI: 1.6-4.2), insufficient gestational weight gain (aOR: 1.9, 95% CI: 1.1-3.1), and exposures to hyperthermia (aOR: 2.3, 95% CI: 1.2-4.3), common cold (aOR: 6.8, 95% CI: 3.6-12.7), and analgesic/antipyretic drugs (aOR: 3.6, 95% CI: 1.3-10.0). Our high rate probably results from exposures to preventable risks, most related to FA, indicating a need for strengthening existing FA-related programs in Mexico.

Maternal use of folic acid and multivitamin supplements and infant risk of birth defects in Norway, 1999-2013

The association between folic acid supplementation and birth defects other than neural tube defects (NTD) remains unclear. We used a log-binomial regression model to investigate if periconceptional folic acid and/or multivitamin use was associated with birth defects in Norway with prospectively collected data from the Medical Birth Registry of Norway (MBRN) during 1999-2013. We used the European Surveillance of Congenital Anomalies (EUROCAT) classification system to define eleven organ-specific major birth defect groups (nervous system, eye, ear-face-neck, cardiovascular system, respiratory system, oral clefts, digestive system, abdominal wall, urinary system, genital organs and limb), with additional subgroups. Fetuses or infants whose mothers used folic acid and/or multivitamin supplements before and during pregnancy were classified as exposed. During the years 1999-2013, 888 294 (99·0 %) live-born infants, 6633 (0·7 %) stillborn infants and 2135 (0·2 %) fetuses from terminated pregnancies due to fetal anomalies were registered in the MBRN. Among the live- and stillborn infants of women who used vitamin supplements compared with infants of non-users, the adjusted relative risk (aRR) was 0·94 (95 % CI 0·91, 0·98) for total birth defects (n 18 382). Supplement use was associated with reduced risk of abdominal wall defects (aRR 0·58; 95 % CI 0·42, 0·80, n 377), genital organ defects (aRR 0·81; 95 % CI 0·72, 0·91, n 2299) and limb defects (aRR 0·81; 95 % CI 0·74, 0·90, n 3409). Protective associations were also suggested for NTD, respiratory system defects and digestive system defects although CI included the null value of 1. During the full study period, statistically significant associations between supplement use and defects in the eye, ear-face-neck, heart or oral clefts were not observed.

Preconception Folic Acid Supplement Use in Immigrant Women (1999-2016)

This study examines how preconception folic acid supplement use varied in immigrant women compared with non-immigrant women. We analyzed national population-based data from Norway from 1999–2016, including 1,055,886 pregnancies, of which 202,234 and 7,965 were to 1st and 2nd generation immigrant women, respectively. Folic acid supplement use was examined in relation to generational immigrant category, maternal country of birth, and length of residence. Folic acid supplement use was lower overall in 1st and 2nd generation immigrant women (21% and 26%, respectively) compared with Norwegian-born women (29%). The lowest use among 1st generation immigrant women was seen in those from Eritrea, Ethiopia, Morocco, and Somalia (around 10%). The highest use was seen in immigrant women from the United States, the Netherlands, Denmark, and Iceland (>30%). Folic acid supplement use increased with increasing length of residence in immigrant women from most countries, but the overall prevalence was lower compared with Norwegian-born women even after 20 years of residence (adjusted odds ratio: 0.63; 95% confidence interval: 0.60–0.67). This study suggests that immigrant women from a number of countries are less likely to use preconception folic acid supplements than non-immigrant women, even many years after settlement.

Homocysteine and disease: Causal associations or epiphenomenons?

Nutritional and genetic deficiencies of folate and vitamin B₁₂ lead to elevation of cellular homocysteine (Hcy), which translates in increased plasma Hcy. The sources and role of elevated plasma Hcy in pathology continues to be a subject of intense scientific debate. Whether a cause, mediator or marker, little is known about the molecular mechanisms and interactions of Hcy with cellular processes that lead to disease. The use of folic acid reduces the incidence of neural tube defects, but the effect of Hcy-lowering interventions with folic acid in cardiovascular disease and cognitive impairment remains controversial. The fact that levels of Hcy in plasma do not always reflect cellular status of this amino acid may account for the substantial gaps that exist between epidemiological, intervention and basic research studies. Understanding whether plasma Hcy is a mechanistic player or an epiphenomenon in pathogenesis requires further investigation, and this research is essential to improve the assessment and potential treatment of hyperhomocysteinemias.