A Second Common Mutation in the Methylenetetrahydrofolate Reductase Gene: An Additional Risk Factor for Neural-Tube Defects?

Am J Hum Genet. 1998 May;62(5):1044-51. doi: 10.1086/301825.

Abstract

Recently, we showed that homozygosity for the common 677(C-->T) mutation in the methylenetetrahydrofolate reductase (MTHFR) gene, causing thermolability of the enzyme, is a risk factor for neural-tube defects (NTDs). We now report on another mutation in the same gene, the 1298(A-->C) mutation, which changes a glutamate into an alanine residue. This mutation destroys an MboII recognition site and has an allele frequency of .33. This 1298(A-->C) mutation results in decreased MTHFR activity (one-way analysis of variance [ANOVA] P < .0001), which is more pronounced in the homozygous than heterozygous state. Neither the homozygous nor the heterozygous state is associated with higher plasma homocysteine (Hcy) or a lower plasma folate concentration-phenomena that are evident with homozygosity for the 677(C-->T) mutation. However, there appears to be an interaction between these two common mutations. When compared with heterozygosity for either the 677(C-->T) or 1298(A-->C) mutations, the combined heterozygosity for the 1298(A-->C) and 677(C-->T) mutations was associated with reduced MTHFR specific activity (ANOVA P < .0001), higher Hcy, and decreased plasma folate levels (ANOVA P <.03). Thus, combined heterozygosity for both MTHFR mutations results in similar features as observed in homozygotes for the 677(C-->T) mutation. This combined heterozygosity was observed in 28% (n =86) of the NTD patients compared with 20% (n =403) among controls, resulting in an odds ratio of 2.04 (95% confidence interval: .9-4.7). These data suggest that the combined heterozygosity for the two MTHFR common mutations accounts for a proportion of folate-related NTDs, which is not explained by homozygosity for the 677(C-->T) mutation, and can be an additional genetic risk factor for NTDs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenine*
  • Adult
  • Cytosine*
  • Female
  • Homocysteine / blood
  • Humans
  • Male
  • Methylenetetrahydrofolate Reductase (NADPH2)
  • Middle Aged
  • Neural Tube Defects / enzymology*
  • Neural Tube Defects / genetics*
  • Oxidoreductases Acting on CH-NH Group Donors / genetics*
  • Oxidoreductases Acting on CH-NH Group Donors / metabolism
  • Point Mutation*
  • Prevalence
  • Pyridoxine / blood
  • Vitamin B 12 / blood

Substances

  • Homocysteine
  • Cytosine
  • Oxidoreductases Acting on CH-NH Group Donors
  • Methylenetetrahydrofolate Reductase (NADPH2)
  • Adenine
  • Pyridoxine
  • Vitamin B 12