ABSTRACT Neural tube defects (NTDs) are the second most common type of structural birth defects in humans, resulting from the failure of neural tube closure (NTC) during neurulation. The etiology of NTDs are known to be multi- factorial, including interacting genetic and environmental factors. There are multiple developmentally-related signaling pathways involved as NTC proceeds spatially and temporally. The identification of specific genetic variants that contribute significantly to the etiology of NTDs, and the characterization of their underlying molecular and cellular mechanisms leading to failed NTC has progressed slowly over the last several decades. What is important to recognize is that NTDs stand out as a preventable birth defect. Research spanning decades demonstrates that maternal periconceptional supplementation with folic acid can reduce the risk of NTDs by 30% to 70%. Yet not all NTDs are folate responsive. Currently between 30-50% of all NTDs are not preventable by folic acid supplementation. The proposed research project is based on our recently published folic acid non- responsive Slc25a32 null mouse model, and its interaction with a folic acid responsive Wnt co-receptor, Lrp6 mutant mouse model. The studies are designed to help elucidate the underlying mechanisms characteristic of folic acid resistant NTDs, and to test our hypothesis that these folate resistant NTDs may be prevented by interventions with downstream folate metabolites, such as formate. It was recently determined that formate could rescue folic acid-resistant NTD mice, suggesting that mitochondrial one carbon metabolism might be compromised in the non-folate responsive NTD population. Despite almost 40 years of intensive study, we still do not fully understand the molecular, cellular and biochemical mechanisms that underlie the folate-dependent process of NTC. This gap in our knowledge hinders our ability to make informed health policy decisions about folate fortification and to identify novel treatments to prevent folate-resistant NTDs.