Assessment of the methylation pathway is critical in understanding the optimal metabolism of methionine and homocysteine. Methionine is an amino acid critical for cellular methylation of DNA and neurotransmitters, transsulfuration, and folate-dependent transmethylation. The most often recognized concerns with inefficient metabolism of methionine are increased risk of cardiovascular disease, cancer, autoimmunity, mood disorders, neurodegeneration, birth defects, poor detoxification, and autism.

Metabolism of Methionine to Homocyteine

Baseline labs we run on new patients and as part of an annual review may include: Homocysteine, Methyl B12, Vitamin B6, Folic acid, and MTHFR. Methionine metabolism is a multi-step process with Homocysteine as an end product of the cycle, that is easily measured in standard labs. Since Homocysteine is used to recycle methionine, elevations in Homocysteine will predict blunting of the methionine and methylation cycle. It is also critical to test for vitamin B12, as a deficiency will also cause a significant increase in Homocysteine levels and blunting of the methylation cycle.

Causes of Elevated Homocysteine

Methionine metabolism defects, often signified by elevated or suboptimal homocysteine levels, are associated with nutritional and vitamin deficiencies, normal aging, environmental toxicants, lead toxicity, and genetics. Evaluating vitamin B12, B6, and Folic acid levels associated with the methylation pathway is easily accomplished through normal lab testing. Environmental testing can be done as a part of a Toxic Metals Chelation challenge to evaluate for lead burden. But for a large percent of individuals, genetics may also be involved.


A large percent of the population carries a polymorphism in an enzyme called 5,10 methyltetrahydrofolate reductase or MTHFR. This polymorphism results in a decline in a number of events that require sufficient folic acid. The effect of this enzyme defect results in a decline of the MTHFR enzyme by approximately 60 percent, leaving the folic acid cycle very sluggish. Folic acid comes in two common forms outside the body known as folate and folic acid. Folic acid status in the US has improved since 1998 when it was added to fortified foods, yet studies show that many people are still deficient in folic acid. Folic acid is essential for the synthesis of purines (the building blocks of DNA), the synthesis of methionine (important in methylation and over 100 reactions requiring SAMe), production of many neurotransmitters, and very importantly, metabolism of homocysteine. Folic acid is absorbed by the gut and is converted to tetrahydrofolate which is converted to methylene tetrahydrofolate and then to methyltetrahydrofolate by the enzyme MTHFR. If the MTHFR polymorphism is present then the pathways reducing homocysteine to methionine, glutathione, phospholipids, and neurotransmitters is reduced by up to 60 percent.

Folic acid deficiency has been linked in numerous studies with depression. It is estimated that 1/3 of all depressed patients have as the sole cause of their depression, a folate deficiency. Studies which have added folic acid to the current antidepressant prescription also showed significant improvement in depression. In addition, studies have also found folic acid deficiency to cause low serotonin(and subsequently low melatonin), which is the brain’s major antidepressant neurotransmitter.

The good news about the folate pathway, it is maintained simply by high doses of folic acid, which will drive the pathway, just like water spilling over a dam, or by taking the form of folic acid that bypasses the need for MTHFR, called 5 Methyltetrahydrofolate (5-MTHF). Other cofactors that also help drive the folate cycle are essential and include vitamins B2 (riboflavin), B6 (pyridoxine), and B12 (methylcobalamin). Patients with depression, without a MTHFR defect, but who are folic acid deficient, will be benefited by taking additional folic acid as contained in a multivitamin mineral complex or methylated B-Complex. Those with the MTHFR are recommended to take a specifically formulated blend of methylated folic acid and co-factors required to maximize folic acid and methionine pathways.

For so many patients who have lived years or decades without knowing they had a MTHFR defect, it is imperative to treat it correctly now. A single blood draw is all that is required to determine the presence of MTHFR. Those who have any symptom of MTHFR polymorphism, or extended family history, should be tested and treated. Click to view DNA Methylation Pathway SNP’s Sample Report. Once the evidence of SNP’s has been determined and supplemental support has been added future evaluation can include specific nutrient levels of the methylation cycle including methionine, homocysteine, S-Adenosyl homocysteine, S-Adenosylmethionine, and cystathionine. Click to view a Methylation Profile Sample Report.