Spina bifida is shown on the left, in magnetic resonance imaging (MRI), showing the open spine and exposed spinal nerves (arrow). This and other Neural tube defects (NTDs) are due to a complex interaction of genetic predisposition and environmental factors, including the addition of methyl groups to DNA. A major source of methyl groups is the vitamin, folic acid. On the right is a map of DNA methylation across all genomic DNA from one individual. Such maps from patients with spina bifida will be compared with healthy controls to determine which genes are under- or over- methylated in affected patients and could contribute to their risk of having an NTD.