Neural tube defects, methylenetetrahydrofolate reductase mutation, and north/south dietary differences in China.

There is a well-recognized correlation between methylenetetrahydrofolate reductase (MTHFR) C677T mutation homozygosity, elevated plasma homocysteine, and increased risk of neural tube defects (NTDs). This risk is modulated by maternal and fetal folate levels provided provided by diet or supplement. Although the frequencies of the C677T mutation are nearly identical between north and south China, the incidence of NTDs is nearly 5 times greater in the north than in the south. This dramatic difference appears related to the fact that dietary sources of folate are more plentiful and varied in South China.