A Polymorphism, R653Q, in the Trifunctional Enzyme Methylenetetrahydrofolate Dehydrogenase/Methenyltetrahydrofolate Cyclohydrolase/Formyltetrahydrofolate Synthetase Is a Maternal Genetic Risk Factor for Neural Tube Defects: Report of the Birth Defects Research Group  Lawrence C. Brody, Mary Conley, Christopher Cox, Peadar N. Kirke, Mary P. McKeever, James L. Mills, Anne M. Molloy, Valerie B. O’Leary, Anne Parle-McDermott, John M. Scott, Deborah A. Swanson  The American Journal of Human Genetics  Volume 71, Issue 5, Pages 1207-1215 (November 2002) DOI: 10.1086/344213 Copyright © 2002 The American Society of Human Genetics Terms and Conditions

Figure 1 Role of MTHFD1 in DNA synthesis. The main role for MTHFD1 (shaded) is in providing 10-formyl THF and 5,10-methylene THF for purine and pyrimidine synthesis. 10-Formyl THF can be synthesized directly from formate and THF, via the synthetase activity, or from 5,10-methenyl THF, via the cyclohydrolase activity, which is channeled from 5,10-methylene THF via the dehydrogenase activity. MTHFD1 plays an indirect role in homocysteine metabolism by providing some of the 5,10-methylene THF pool, but the major source of this is SHMT. The enzymes MTHFR and MS are directly involved in homocysteine metabolism. The American Journal of Human Genetics 2002 71, 1207-1215DOI: (10.1086/344213) Copyright © 2002 The American Society of Human Genetics Terms and Conditions