MTHFR gene testing

• MTHFR gene testing is not recommended in routine general practice.
• There is no substantial evidence that testing common MTHFR variants improves patient outcomes.
• Knowing a patient’s MTHFR status is unlikely to change management.
• RACGP advises GPs to avoid requesting MTHFR gene testing, because there is no causal link between common MTHFR variations and particular diseases, and no evidence-based treatment that improves outcomes based on the result.
• RCPA also recommends against MTHFR testing for common disorders in people receiving a normal folate-fortified diet.

2. What is MTHFR?

• MTHFR stands for methylenetetrahydrofolate reductase.
• It is an enzyme involved in folate metabolism.
• Folate is important for many biochemical reactions in the body.
• The MTHFR gene helps process amino acids, particularly through its role in folate metabolism.

3. Common MTHFR variants

• The two commonly discussed MTHFR variants are:
  • C677T / p.Cys677Thr
  • A1298C / p.Ala1298Cys
• These variants are common in the general population.
• Around 65% of people have at least one of these variants.
• These variants can be associated with mildly increased homocysteine, but this usually does not translate into clinically useful disease prediction or treatment change.

4. Why MTHFR testing became popular

MTHFR testing is often promoted, especially by some complementary and alternative practitioners, for conditions such as:

• infertility
• recurrent pregnancy loss
• thrombophilia / clotting risk
• cardiovascular disease
• autism spectrum disorder
• mental health concerns
• cancer risk
• general “genetic risk” assessment

However, the problem is that association does not equal causation, and the test usually does not change treatment.

5. Evidence problem: association is weak and inconsistent

• MTHFR variants have been studied in many conditions, including:
  • thromboembolism
  • stroke
  • peripheral artery disease
  • migraine
  • hypertension
  • miscarriage
  • infertility
  • neural tube defects
  • cancer
  • psychiatric disorders
  • chemotherapy toxicity
• Evidence is often conflicting.
• Many common diseases are multifactorial, involving:
  • genetics
  • diet
  • lifestyle
  • comorbidities
  • environmental factors
• Folate metabolism is complex, and dietary folate intake can influence the effect of MTHFR variants.

6. Analytical validity, clinical validity and clinical utility

Analytical validity

• This is about the technical accuracy of the test.
• For MTHFR testing, analytical validity is good because the lab can accurately identify the common MTHFR variants. In simple terms:
• “Does the test correctly detect the gene variant?”
• For MTHFR: yes, it can detect the variant

Clinical validity

Question: Does the test result actually relate to the disease or condition we are worried about?

• This is about whether the result has a meaningful relationship to disease.
• For MTHFR testing, clinical validity is uncertain/weak.
• Some studies show associations with conditions, but evidence is conflicting.
• Many conditions are multifactorial, involving:
  • genetics
  • diet
  • lifestyle
  • folate intake
  • other medical risk factors
• In simple terms:
  “If the test is positive, does that mean the patient is likely to have or develop the disease?”
• For common MTHFR variants: not reliably

Clinical utility

Question: Does the test result change management or improve outcomes?

• This is the most important question in GP.
• A test may be technically accurate, but still not useful if it does not change treatment.
• For MTHFR testing, clinical utility is not demonstrated.
• The result usually does not change:
  • diagnosis
  • treatment
  • prevention advice
  • referral pathway
  • pregnancy folic acid advice
• In simple terms:
  “Will this test result help me do something different that benefits the patient?”
• For common MTHFR variants: usually no.

Practical conclusion

• The test may detect a variant, but it usually does not help diagnose disease, predict risk reliably, or guide treatment.

7. Homocysteine and MTHFR

• Common MTHFR variants can be associated with mildly increased homocysteine.
• Mild homocysteine elevation was previously thought to be linked with:
  • thrombophilia
  • cardiovascular disease
  • recurrent pregnancy loss
• More recent evidence does not support using this as a clinically useful basis for MTHFR testing.
• Homocysteine can also be affected by:
  • diet
  • lifestyle
  • smoking
  • overweight
  • other genetic factors

Practical GP point

• If homocysteine is clinically relevant, a biochemical homocysteine test may be more useful and less expensive than MTHFR genetic testing.
• However, routine homocysteine testing itself should still be guided by the clinical scenario.

8. Pregnancy, miscarriage and folic acid

Key points

• MTHFR testing is not recommended as part of evaluation for:
  • early pregnancy loss
  • recurrent miscarriage
  • thrombophilia assessment
• MTHFR status does not change the recommendation for folic acid supplementation.
• Women planning pregnancy or in the first trimester should take standard folic acid supplementation to reduce neural tube defect risk.
• This applies regardless of MTHFR status.

Australia-specific point

• In 2009, Australia introduced mandatory folate fortification of wheat flour used for bread.
• This reduced the number of people with low red-cell folate levels.
• Folate fortification further reduces the likely value of routine MTHFR testing in people eating a normal Australian diet.

9. When MTHFR testing should not be ordered

Do not order MTHFR testing for routine evaluation of:

• thrombophilia
• venous thromboembolism risk
• early pregnancy loss
• recurrent miscarriage
• infertility
• cardiovascular disease risk
• migraine
• hypertension
• autism spectrum disorder
• mental health concerns
• cancer risk
• general genetic screening
• vague fatigue or “methylation” concerns

Reason:

• no proven causal link
• no evidence-based treatment change
• no improvement in clinical outcomes
• risk of unnecessary anxiety and cost

10. Important exception: homocystinuria

• Common MTHFR polymorphisms are not the same as rare metabolic disorders causing marked homocysteine elevation.
• If homocystinuria is suspected, especially in a newborn, appropriate paediatric referral or repeat screening may be required.
• This is a different clinical situation from routine MTHFR testing in adults.

11. Harms of MTHFR testing

MTHFR testing can cause harm through:

• unnecessary investigations
• patient anxiety
• pregnancy-related worry about neural tube defects or miscarriage
• parental distress and unnecessary testing in children
• false reassurance where proper screening or prevention is needed
• unnecessary financial cost
• genetic labelling or stigma

RCPA notes that the test itself has little physical risk, but the larger concern is the cost and the risk of labelling someone as having a genetic disorder despite lack of robust evidence.

12. Medicare / cost

• MTHFR testing is generally not covered by the Medicare Benefits Schedule.
• It cannot be bulk billed when requested for common MTHFR variants because the result does not change treatment.
• Patients may access testing privately at their own expense.

13. Genetics referral

• There is usually no indication to refer to genetics services for common MTHFR variants.
• Because of poor clinical utility, some genetics services no longer accept referrals for MTHFR-related consultations.

14. What to do instead

Explore the patient’s reason for requesting the test

Ask:

• “What are you hoping this test will explain?”
• “Are you worried about miscarriage, clots, fertility, fatigue, or family risk?”
• “Has someone advised you that this result would change your treatment?”

Manage the actual clinical concern

Examples:

• Recurrent miscarriage: assess according to recurrent pregnancy loss pathways; consider appropriate obstetric/gynaecology referral.
• Thrombosis history: assess personal and family history, provoking factors, and indications for thrombophilia testing according to guidelines.
• Cardiovascular risk: use absolute CVD risk assessment and manage BP, lipids, smoking, diabetes, weight and lifestyle.
• Pregnancy planning: provide standard folic acid advice.
• Fatigue/non-specific symptoms: assess common causes such as anaemia, thyroid disease, sleep, mood, medication effects and lifestyle factors.

Continue standard preventive care

• healthy balanced diet
• smoking cessation
• weight management
• exercise
• management of comorbidities
• standard folic acid supplementation for women of childbearing age
• appropriate screening based on age, sex, family history and clinical risk

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Bottom line

• Do not routinely order MTHFR genetic testing.
• Do not use MTHFR testing to assess thrombophilia, miscarriage, infertility, cardiovascular disease, autism, mental illness, cancer risk or vague non-specific symptoms.
• Standard folic acid advice applies regardless of MTHFR status.
• Manage the patient’s actual clinical problem using evidence-based assessment and treatment.
• Testing common MTHFR variants usually adds cost and anxiety without changing management.