MTHFR is an enzyme responsible for converting 5,10 methylenetetrahydyrofolate to the product 5-methyltetrahydrofolate-it is invovled in the metabolism of folate and homocysteine. The product of the reaction catalyzed by MTHFR coverts homocysteine (a potentially toxic amino acid) to methionine (a useful and necessary amino acid).
Why is this important?
Certain mutations in this gene can lead to increased homocysteine levels especially when folate is low. High homocysteine is a risk factor for heart and vascular disease.
People with this gene mutation should not be taking folic acid supplements or food with folic acid enriched because they cannot metabolize it. They need L methyl folate instead. In fact methylation is a challenge for these people and methylation is very important for detoxing heavy metals.
Spectracell has an excellent test for the MTHFR genotype so that you can know if methylation is a challenge and know if you should not be taking folic acid.
I also recommend you visit the website MTHFR.net for excellent information on this subject.