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About MTHFR – Information for GPs

About MTHFR – Information for GPs
(MTHFR = Methylenetetrahydrofolate Reductase)


In summary

  1. MTHFR variants are very common in the general population.
  2. MTHFR variant C667T is considered a strong determinant of folate status in women of reproductive age 1 and has been associated with lower levels of red blood cell folate and elevated homocysteine. MTHFR acts in association with a number of other genes as a threshold risk factor, and is not usually individually significant.
  3. Folic acid supplementation has been shown to increase folate levels, regardless of MTHFR status,  to that which is considered protective for neural tube defects 2.
  4. MTHFR variants are unlikely to have any impact on health in the absence of low red blood cell folate or high homocysteine. 
  5. MTHFR status does not change the recommendation for women to take folic acidsupplementation at least 1 month prior to conception, as per general guidelines.



The MTHFR gene encodes an enzyme in the methylation cycle (See Fig 1).

MTHFR (‘5,10-methylenetetrahydrofolate reductase’) converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, and is an important cofactor in the biosynthesis of SAMe (S-adenosyl methionine), the primary methyl donor involved in regulating gene expression.

Fig 1 - The Methylation Cycle:  Taken from


A number of variants have been identified in the MTHFR gene.  The two most commonly reported variants are C677T and A1298C.  These variants are common among the general population.

Last updated: Aug 05, 2015