|MadSci Network: Biochemistry|
You have asked a question which is central to a very major field of current research. I'll try to summarize some of the information that is out there, and then I will point you to some more in depth studies.
Folic acid is simply a stable form of folate that is biologically
accessible. So, the question really is "What is the role of folate in
development?" Apparently, the role of folate is actually as a part of
the cycle which results in the remethylation of homocysteine as the picture
below demonstrates [adapted from Eskes, 1998. Nutrition Reviews
It is known that mothers with increased levels of homocysteine (hyperhomocysteinemia) in their blood have a tendency to have offspring with neural tube defects (NTDs). Also, hyperhomocysteinemia can result from specific mutations in the enzyme 5,10-methylenetetrahydrofolate reductase (MTHFR in the figure above). Genetically caused hyperhomocysteinemia can be normalized with folic acid in the diet (all as reviewed in Eskes, 1998).
Homocysteine appears to be a teratogen. When amounts of homocysteine equivalent to those found in hyperhomocysteinemic mothers are applied to early developing chick embryos, a significant proportion of those embryos develop NTDs (Rosenquist et al., 1996. PNAS 93:15227- 32). The molecular mechanism of this effect is not currently understood.
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