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Comorbidity of 5,10-methylenetetrahydrofolate reductase and methionine synthase gene polymorphisms and risk for neural tube defects
  2. T TAMURA*,
  1. *Department of Nutrition Sciences, 340 Webb Building, The University of Alabama at Birmingham, Birmingham, Alabama 35294-3360, USA
  2. †The Center for Obstetric Research, Department of Obstetrics and Gynecology, The University of Alabama at Birmingham, Birmingham, Alabama, USA
  1. Dr Johanning, garyj{at}

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Editor—Neural tube defects (NTDs) are among the most common and devastating birth defects. NTDs result from an incomplete closure of the neural tube, and include malformations of the skull, brain, meninges, spinal cord, and vertebral column. Recent evidence suggests that closure of the neural tube occurs in five separate sites which then fuse during the fourth week of gestation; NTDs occur when one site fails to close or two sites fail to fuse.1

During the last decade, periconceptional folic acid supplementation has been shown to reduce the risk of occurrence2 and recurrence3 of NTDs. Women with an NTD affected pregnancy do not usually have overt signs of folate deficiency, although decreased erythrocyte folate concentration, the index known to reflect whole body folate stores, has been reported.4 5 In addition, it has been reported that women with NTD pregnancies have raised homocysteine concentrations in plasma and amniotic fluid,6 7 suggesting that folate metabolism may be altered in these women.

5,10-methylenetetrahydrofolate reductase (MTHFR) catalyses the reaction from 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, which serves as methyl donor for the remethylation of homocysteine to methionine.8 A substitution (C to T) at the highly conserved nucleotide 677 of theMTHFR gene has been described, which results in the conversion of an alanine (Ala) to a valine (Val) residue and increased in vitro thermolability of the enzyme.9 In vivo, the thermolabile MTHFR mutant is known to result in raised plasma homocysteine concentrations when folate nutriture is inadequate.10 The frequency of homozygosity for this mutation is approximately 9% for various populations, but is higher in French Canadian, Italian, and Hispanic populations, and lower in African-American populations.9 11-13

The C677T mutation has been reported to be a genetic risk factor for NTDs.11 14-17 However, the significance of …

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