The genetics of folate and vitamin B12 metabolism relate

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Research in the Molecular Pathogenesis is focused on defining changes in the genes that underlie inherited susceptibilities to common diseases such as cancer and birth defects. Changes in folate metabolism are correlated tumor formation and birth defects. Folate genes are also involved in the methylation of DNA and proper brain function. . We are searching for genetic variants in genes related to folate, methionine and homocysteine metabolism. Individuals affected with cancer or Spina Bifida (one form of neural tube defects) will be tested for these variants. Variants found at higher frequency in individuals with disease will help us identify genes associated with risk. In the past we have tested more than 15 genes for variants that might perturb folate metabolism and therefore be associated with an increase risk of having a child with an neural tube defect. We found that variants in one of these genes, TC2, appear to affect the levels of vitamin B12 in the blood during pregnancy. This finding may be related to birth defects and also may help to explain why some elderly individuals become anemic and suffer neurological symptoms from vitamin B12 deficiency. We also found that mothers carrying a specific variant in a second gene, MTHFD1, have a 50% increased risk bearing a child with a neural tube defect. This previously un-described variant may be responsible for up to 25% of all neural tube defects. Approximately one in five individuals in the population carry one of these risk factors. We recently determined that this particular variant was also an risk factor for placental abruption a common cause of miscarriage and for misscarriages that occur in the second trimester. We have re-created these genes in the laboratory and are currently using an experimental system to determine exactly how these variants alter the function of these proteins. Experiments completed in the last year have revealed that the different forms of TC2 bind vitamin B12 with different affinities. These data may explain the differences that we and others observe in plasma levels of vitamin B12. We have expanded these studies to include the molecule responsible for transporting vitamin B12 into the cell. We have preliminary data that suggests that variants in this transporter are associated with a risk of having a child with an NTD. We are currently carrying out experiment aimed determining which of the many variants in this gene is actually causing the increased risk. In the past year we began to investigate the relationship between folate, vitamin B12 and DNA methylation. Little is known about inter-individual variation in DNA methylation. We developed an assay that allows us to measure the extent of methylation by carrying out DNA sequencing. We are currently evaluating this technique. If sucessful, this method will allow us to map methylation sites in the genome at high resolution. A detailed knowledge of the function of the the genes in the folate/vitamin B12 metabolic pathways will add to our understanding of neural tube defects and potentially help guide public health policy in the area of nutritional supplementation.