Methylenetetrahydrofolate Reductase (MTHFR)

MTHFR C667T is an autosomal recessive mutation within the MTHFR gene that results in the production of a thermolabile enzyme with decreased activity for methylating homocysteine. This mutation involves a single nucleotide substitution of thymidine for cytosine at nucleotide position 667 of the MTHFR gene. Carriers of this mutation are associated with elevated levels of homocysteine in plasma, which, in turn, increases the risk of arterial disease and venous thrombosis.

The prevalence of the MTHFR C667T mutation in the general population is estimated to be 10-15%. However, for patients with a history of familial hyperhomocysteinemia, there is an estimated 28% incidence of homozygosity for this mutation. MTHFR C667T heterozygosity has a reported incidence of approximately 45% in the Caucasian population. This genotype, however, is not reported to significantly increase homocysteine levels.

The MTHFR gene mutation test may be helpful in determining the cause of hyperhomocysteinemia. However, we do not recommend the test as first line screening for this condition.