Methylation in Depth: Genotype, Phenotype and Clinical Overreach

An earlier article introduced folate, methylation, MTHFR and homocysteine, and explained why routine MTHFR testing is not recommended. This article goes deeper into the biochemistry of methylation, the difference between genotype and phenotype, and the forms of clinical overreach that have grown up around the subject. Methylation is genuinely central to human biology, which is exactly why it attracts overconfident claims.

What methylation does

Methylation is the transfer of a single carbon methyl group from a donor, mainly S adenosylmethionine, SAMe, to another molecule. It is involved in:

• Epigenetic regulation: methylation of DNA and histones controls gene expression.
• Phospholipid synthesis: the liver enzyme PEMT uses methyl groups to make phosphatidylcholine, essential for cell membranes and for exporting fat from the liver.
• Creatine synthesis: a major consumer of methyl groups in the body.
• Neurotransmitter metabolism: the enzyme COMT methylates catecholamines such as dopamine and noradrenaline, and catechol oestrogens.
• Other reactions, including some detoxification pathways.

After donating its methyl group, SAMe becomes S adenosylhomocysteine, SAH, which is converted to homocysteine. The ratio of SAMe to SAH is sometimes described as the methylation potential of a cell; high SAH inhibits many methylation reactions.

Methyl donors in the diet

Methyl groups come from several dietary sources: folate, working with vitamin B12; choline, found in eggs, meat, fish, soy and some vegetables; betaine, found in beetroot, spinach and whole grains; and methionine from protein. Choline requirements rise in pregnancy, and many people, particularly those eating few eggs or animal foods, have intakes below recommended levels. Choline is sometimes overlooked in discussions focused on folate.

Genotype and phenotype

Consumer genetic panels often report variants in several methylation related genes.

The key point is that genotype does not equal phenotype. Common variants have small effects that depend heavily on nutrient intake, and many people with several variants have normal homocysteine and normal health. Phenotype, what is actually happening in the body, is better assessed with measurable markers.

Phenotype markers

• Homocysteine: reflects the combined status of folate, B12 and B6, kidney function and other factors.
• Vitamin B12, active B12 and methylmalonic acid: assess B12 status.
• Serum or red cell folate.
• SAMe and SAH: research measures, not routine clinical tests.
• Dietary assessment: folate, B12, choline and protein intake.

Forms of clinical overreach

Diagnosing from genotype

Labelling patients as poor methylators or assigning complex diagnoses on the basis of common variants is not supported by evidence.

Overmethylation and undermethylation

Some practitioners classify patients as overmethylators or undermethylators based on symptoms, genotypes or tests such as whole blood histamine, and link these categories to psychiatric symptoms and personality traits. These concepts and tests have not been validated in controlled research.

High dose protocols

Protocols combining high doses of methylfolate, methylcobalamin, SAMe, betaine and other supplements are sometimes prescribed on the basis of genotype. Evidence of benefit is lacking for most indications, and high doses are not without concern. Some people report anxiety, irritability or insomnia when taking high dose methylated supplements, though these reports are largely anecdotal.

Ignoring basic deficiencies

Focusing on genetic variants can distract from common, measurable problems: B12 deficiency from metformin, acid suppressants or vegan diets; folate deficiency; inadequate choline in pregnancy; kidney disease raising homocysteine.

Questions about high intakes

High folic acid intakes can mask B12 deficiency, and unmetabolised folic acid appears in the blood with high intakes; its significance is uncertain. High serum B12 levels are sometimes found in people with liver disease, kidney disease or cancer, most likely as a consequence rather than a cause, but an unexplained very high B12 in someone not taking supplements warrants medical assessment. These uncertainties are a reason for proportionate rather than maximal supplementation.

Where methylation related interventions have evidence

• Folic acid before conception to prevent neural tube defects.
• Treatment of B12 and folate deficiency.
• Adequate choline in pregnancy, recommended by several nutrition bodies.
• Management of rare inherited disorders of homocysteine metabolism under specialists.
• L methylfolate as an adjunct in some people with depression, with modest evidence.
• Folic acid for stroke prevention in populations with low folate status and hypertension, as shown in a large Chinese trial.

An illustrative case

A 38 year old woman with anxiety, insomnia and fatigue has been told by a practitioner that she is a poor methylator based on a genetic panel showing variants in MTHFR, COMT and MTRR. She is taking high dose methylfolate, methylcobalamin, SAMe and several other supplements, and her anxiety and insomnia have worsened since starting. Her homocysteine, B12 and folate are normal; her ferritin is low and she drinks 5 coffees a day. The high dose supplements are gradually stopped, her iron deficiency is treated, caffeine is reduced and her anxiety is addressed with cognitive behavioural therapy. Over 3 months her sleep and anxiety improve. Her genes had not changed; the plan had.

Central biology, careful claims

Methylation is fundamental to human health, and its biochemistry is worth understanding. But genotype panels and unvalidated tests do not reliably reveal how methylation is working in an individual, and high dose protocols built on them lack evidence. Measurable markers, adequate nutrition and attention to common deficiencies provide a more reliable, and safer, foundation.