PGx: Folate metabolism

MTHFR efficiency and folic acid

Now that you have been tested genetically you may stumble upon the term MTHFR. It is associated with folate/folic acid metabolism. The genetical basis for processing folate has been associated with several diseases. Preventing folate deficency for longer period might postpone or prevent some health conditions. Although the scientist still argue if risks with smaller variations have any effect we might consider adding more natural folate to our diet. Good source for folate-rich foods can be found -> here, but please be aware also about the over hyping of the condition. A good article describing the problem can be found -> here.

Folate is a generic name for both natural and synthetic forms of the B9 vitamin, such as folic acid, folinic acid and 5-methyltetrahydrofolate. It is important in cell growth and function, metabolism of nucleic and amino acid precursors and red blood cell formation. During pregnancy folate has an important role in the development of the brain and spine. It is an essential vitamin and has to be supplied by diet, as humans cannot synthesize folate. (1);(2)

Methylene tetrahydrofolate reductase (MTHFR) is an enzyme coded by the MTHFR gene. It is the key enzyme in folate metabolism and converts folate to a form that is necessary in another reaction – synthesis of methionine from homocysteine. Therefore MTHFR is important not only in folate metabolism but also in maintaining the homeostasis of homocysteine. Mutations in the MTHFR gene can lead to higher than normal levels of homocysteine, a condition called hyperhomocysteinemia.(3);(4)

“It helps to change one amino acid building block, homocysteine, into another, methionine. The problem isn’t the MTHFR, it’s the amount of homocysteine in your blood.”

Genomemag.com – MTHFR: Hope or Hype?

The marker rs1801133 has two alleles, C and T. The T allele is the risk allele associated with lowered MTHFR efficiency. The C allele is the normal allele. (5)

C : C
normal MTHFR efficiency

C : T
65 % MTHFR efficiency
(compared to C : C genotype )

T : T
30 % MTHFR efficiency
(compared to C : C genotype )

The marker rs1801131 has two alleles, A and C. The C allele is the risk allele associated with lowered MTHFR efficiency. The A allele is the normal allele. (6)

A : A
normal MTHFR efficiency

A : C
83 % MTHFR efficiency
(compared to A : A genotype )

C : C
60 % MTHFR efficiency
(compared to A : A genotype)

THE COMBINED EFFECT

As the proportion of the risk alleles is low in the population no people with either homozygosity for the both risk alleles (rs1801133 T : T and rs1801131 C : C) or homozygosity for the one risk allele and heterozygosity for the other risk allele have been detected in the studies. Therefore there is no data about these genetic combinations. The occurrence of these combinations is very unlikely.

The combined heterozygosity ( rs1801133 C : T and rs1801131 A : C ) results in an outcome similar, though somewhat less severe, to rs1801133 homozygotes ( T : T ). (8);(9);(10)

Why does efficiency of MTHFR matter?

As mentioned before, MTHFR is very important in regulation of homocysteine levels. Lowered MTHFR efficiency may lead to elevated homocysteine levels, which is a risk factor for a number of diseases. A great deal of research has been conducted to examine the relationship between MTHFR  mutations, elevated homocysteine levels and disease.

Elevated homocysteine levels are associated with cardiovascular disease, clots in veins, pregnancy complications (neural tube defect) an a number of other conditions.

While reduced MTHFR enzyme function can lead to elevated homocysteine levels it does not necessarily do so, many people have normal levels. The MTHFR mutations in the absence of elevated homocysteine levels are not a risk factor for heart disease, blood clotting and pregnancy complications in countries where food is fortified with folic acid.

Overall a number of studies have looked at MTHFR  mutations and associations with various diseases, in fact over 600 medical disorders have been researched. The studies have been conflicting, some showing associations and others not. Overall the studies have been inconclusive and conflicting and therefore a solid scientific base for MTHFR variants having an effect on health has not been established. (11).

References

are linked in the article and numbered.

Disclaimer

The information provided in this article is based on published SNP (single nucleotide polymorphism) data and is for educational purposes only. Most published studies about genetic variants in the DNA explain only a small part of the heritability of a trait or disease risk, and often do not take into account how different variants may interact with each other. In addition, many published studies do not account for medical history or environmental, dietary, microbial, or lifestyle factors, which may alter true risk for any trait or disease.

The relevance of each article may vary based on ethnicity. Nothing in the genetic article should be used for medical self-diagnosis or self-treatment. The information provided should not be considered complete, nor should it be relied on to suggest diagnosis or treatment of a particular individual. You should always get the advice of your doctor or other appropriate health care professional if you have any questions about diagnosis, treatment, prevention, mitigation, or cure of any medical condition, phenotype, condition, impairment, or the status of your health.

Glossary

ALLELE
An allele is a variant form of a gene that is located at a specific position, or genetic locus, on a specific chromosome. Humans have two alleles at each genetic locus, with one allele inherited from each parent.
CHROMOSOME
A chromosome is a thread-like structure of DNA that carries hereditary information, or genes. Human cells have 22 chromosome pairs plus two sex chromosomes, giving a total of 46 per cell.
DISEASE PREVALENCE
The proportion of individuals in a population having a disease or characteristic. Prevalence is a statistical concept referring to the number of cases of a disease that are present in a particular population at a given time, whereas incidence refers to the number of new cases that develop in a given period of time.
DNA
DNA, or deoxyribonucleic acid, is the main component of chromosomes and the carrier of genetic information in nearly all living organisms. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
GENE
A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome. Genes are transferred from a parent to offspring, and are responsible for the physical and heritable characteristics or phenotype of an individual.
GENETIC VARIANT
An alteration in the most common DNA nucleotide sequence. The variant can be benign, pathogenic or of unknown significance. SNPs are the most common type of genetic variation.
GENOTYPE
The genetic makeup of an individual organism. It may also refer to just a particular gene or set of genes carried by an individual. The genotype determines the phenotype, or observable traits of the organism.
ODDS RATIO
The odds ratio is a way of comparing whether the odds of a certain outcome is the same for two different groups. In this report, the odds ratio estimates the probability of a condition occurring in a group of people with a certain genetic variant compared to a group of people without that variant.

An odds ratio of 1 means that the two groups are equally likely to develop the condition. An odds ratio higher than 1 means that the people with the genetic variant are more likely to develop the condition, while an odds ratio of less than 1 means that the the people with the variant are less likely to develop the condition.
PHENOTYPE
A description of an individual’s physical characteristics, including appearance, development and behaviour. The phenotype is determined by the individual’s genotype as well as environmental factors.
POPULATION ALLELE FREQUENCY
The allele frequency represents the incidence of a gene variant in a population. Alleles are variant forms of a gene that are located at the same position, or genetic locus, on a chromosome.
SNP
Single nucleotide polymorphisms, frequently called SNPs, are the most common type of genetic variation among people. A SNP is a variation in a single nucleotide that occurs at a specific position in the genome.

Translation

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Folate metabolism
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