MTHFR stands for Methylenetetrahydrofolate reductase. Another term for MTHFR is NAD(P)H 5,10-methylenetetrahydrofolate.

The MTHFR gene provides instructions that make the enzyme methylenetetrahydrofolate reductase. This enzyme is important because it helps process amino acids and converts 5,10-methylenetetrahydrofolate to 5-methylenetetrahydrofolate.

5-methylenetetrahydrofolate is important because it converts homocysteine to methionine. This conversion is imperative because high homocysteine levels cause narrowing of the arteries and can lead to excessive blood clotting.

There are several polymorphisms (more than one variation) in the MTHFR gene.
Two of the most investigated polymorphisms are the: C677T and the A1298C mutations.

Individuals with the C677T gene mutation suffer from methylenetetrahydrofolate deficiency. This mutation is associated with heart disease, stroke, high blood pressure, high blood pressure during pregnancy (preeclampsia) and hyperhomocysteinemia.

Hyperhomocysteinemia is when there are high levels of homocysteine in the blood. High levels of homocysteine are associated with coronary artery disease and venous thrombophilia (an abnormality of blood coagulation that leads to clotting).

About 10% of the North American population are homozygous (carry two copies of the gene) for this polymorphism.

The A1298C mutation does not lead to elevated homocysteine levels unless the individual also carries the C677T mutation. However when the MTHFR mutation is present in an individual along with another thrombophilic factor (ie. Factor V Ledien), the risk for thrombophilia is greatly increased.