Impact of 5,10-methylenetetrahydrofolate reductase gene polymorphism on neural tube defects

Neural tube defects (NTDs) are among the most common congenital malformations worldwide. Their etiology and exact mechanisms of development are incompletely understood. Many enzymes involved in folate metabolism and the genes encoding these enzymes have been studied as candidates in their etiology. A mutation in the methylenetetrahydrofolate reductase (MTHFR) gene--a C-->T transition at nucleotide 677--is one among them. The mutation results in substitution of alanine by valine at a functionally important site in the enzyme. It has been shown to be a risk factor for development of NTDs in certain populations. The present study was conducted to evaluate the role of MTHFR 677 C-->T mutation as a risk factor for NTD in the South Indian population and to determine the relative importance of the genotypes in the affected child and its mother.

Blood samples were collected from the test and the control groups. The test group consisted of children with NTDs and their mothers, while the control group consisted of apparently healthy controls. MTHFR C677T polymorphism in the 3 groups was determined by polymerase chain reaction and restriction fragment length polymorphism studies. Comparison of polymorphism in the 3 groups was using the chi-square test.

There was a significant difference in the prevalence of MTHFR 677 C-->T mutation among the 3 groups (p = 0.002). The risk conferred by the TT genotype in the child was statistically significant (OR 12.625, 95% CI 1.430-111.465). In the mothers, however, although there was an increased prevalence of the mutation compared with the control individuals, the difference was not statistically significant (p = 0.152).

The MTHFR 677TT genotype is considered to be a definite risk factor for development of NTDs. It is the TT genotype status of the developing embryo, rather than the TT genotype status of its mother, that is the critical genetic determinant of MTHFR-related NTD risk.