Methylation – Function, Health Effects and Cycle

What is Methylation?

Methylation is a fundamental biochemical process in which a methyl group (–CH₃) is transferred onto a molecule. This process occurs throughout the entire human body and influences a wide range of biological functions, including gene expression, detoxification, neurotransmitter production, and immune function. Methylation is one of the most important concepts in epigenetics – the science that studies how genes are switched on and off without altering the DNA sequence itself.

Types of Methylation

DNA Methylation

DNA methylation involves the addition of a methyl group to a cytosine nucleotide in the DNA double helix, typically at so-called CpG sites. This modification generally leads to the silencing (inactivation) of the affected gene. DNA methylation is critical for normal developmental processes, cell differentiation, and the stable inactivation of one X chromosome in females.

RNA Methylation

RNA molecules can also be methylated. These modifications influence the stability, transport, and translation of RNA, thereby playing an important role in protein biosynthesis.

Protein and Histone Methylation

Proteins, particularly histones (the proteins around which DNA is wrapped), can also be methylated. Histone methylation regulates how tightly DNA is wound around the histones, which in turn affects the accessibility of genes for the transcription machinery.

The Methylation Cycle

The methylation cycle, also known as the one-carbon cycle or methionine cycle, is a complex network of biochemical reactions that ensures the supply of methyl groups in the body. The central molecule is S-adenosylmethionine (SAM), considered the universal methyl group donor. Key nutrients that support this cycle include:

• Folate (Vitamin B9): Essential for the regeneration of methyl groups.
• Vitamin B12 (Cobalamin): A cofactor for the enzyme methionine synthase.
• Vitamin B6 (Pyridoxine): Involved in the conversion of homocysteine.
• Choline and Betaine: Alternative methyl group donors.
• Riboflavin (Vitamin B2): A cofactor for the MTHFR enzyme.

The MTHFR Gene and Methylation Disorders

The enzyme MTHFR (methylenetetrahydrofolate reductase) is a key enzyme in the methylation cycle. Certain genetic variants (polymorphisms) of the MTHFR gene, particularly C677T and A1298C, can reduce enzyme activity and lead to a diminished methylation capacity. This can raise homocysteine levels in the blood, which is associated with an increased risk of cardiovascular disease, neurological disorders, and pregnancy complications.

Importance of Methylation for Health

Balanced methylation is essential for numerous bodily functions:

• Gene regulation: Controls the expression of genes, including tumour suppressor genes.
• Detoxification: Supports the liver in neutralising and eliminating harmful substances.
• Neurotransmitter production: Involved in the synthesis of serotonin, dopamine, and melatonin.
• Immune function: Regulates inflammatory responses and immune cell activity.
• Homocysteine breakdown: Prevents the accumulation of vessel-damaging homocysteine.
• Epigenetic inheritance: Methylation patterns can be passed on across generations.

Hypermethylation and Hypomethylation

An imbalance in methylation status can have significant health consequences. Hypermethylation refers to excessive methylation of genes, leading to their inactivation – this can contribute to the silencing of tumour suppressor genes and the development of cancer. Conversely, hypomethylation involves insufficient methylation of genes, which can result in uncontrolled gene activation and similarly contribute to cancer development or autoimmune diseases.

Diagnostics and Laboratory Values

Methylation capacity can be assessed indirectly through various laboratory parameters:

• Homocysteine levels in the blood: Elevated values may indicate impaired methylation.
• MTHFR genotyping: Detection of relevant gene variants.
• Folate and Vitamin B12 levels: Reflect the availability of essential cofactors.
• SAM/SAH ratio: A direct measure of methylation capacity available through specialised laboratories.

Treatment and Support of Methylation

In cases of confirmed methylation disorders or elevated homocysteine, the following measures may be beneficial:

• Supplementation with active folate (5-MTHF) rather than synthetic folic acid, especially for individuals with MTHFR variants.
• Adequate intake of Vitamin B12, preferably as methylcobalamin.
• Intake of Vitamin B6 and riboflavin as important cofactors.
• A diet rich in natural folate: green leafy vegetables, legumes, and nuts.
• Avoidance of factors that burden the methylation cycle, such as excessive alcohol consumption and smoking.

References

1. Loscalzo J, Handy DE. Epigenetic modifications: basic mechanisms and role in cardiovascular disease. Pulm Circ. 2014;4(2):169-174.
2. Crider KS, Yang TP, Berry RJ, Bailey LB. Folate and DNA methylation: a review of molecular mechanisms and the evidence for folate's role. Advances in Nutrition. 2012;3(1):21-38.
3. World Health Organization (WHO). Folic acid supplementation guidelines. WHO Technical Report. Geneva, 2023. Available at: https://www.who.int