Evidence · Replicated

What the research found

In the cited research, the A allele at rs1801133 was associated with lower serum folate concentrations in the studied cohorts.

GG: Higher average
AG: Middle
AA: Lower average

Slight effect

What the study found

In the study, each copy went with lower serum folate on average.

Icelanders with serum folate measured at two clinical laboratories (1990 to 2011) · 28,913 people · Table 2 (Icelandic column); sample size in the Results study outline

Evidence: Replicated genome-wide association with a coding variant
Who was studied: Icelandic and Danish cohorts

1000 Genomes Project

How common each genotype is

How common each genotype is in the 1000 Genomes Project, by region
Region	GGHigher average	AGMiddle	AALower average
All regions2,504 people	59%	33%	8%
Africa661 people	83%	16%	1%
The Americas347 people	26%	53%	21%
East Asia504 people	51%	38%	11%
Europe503 people	41%	46%	14%
South Asia489 people	77%	22%	<1%

Among the 2,504 people of the 1000 Genomes Project, in five world regions. These percentages describe groups of people, never anyone’s chance of having a trait.

Ancient genomes

Through time

How often the studied letter was read in ancient people, era by era, in the region chosen.

Region

Through time: Europe
Before farmingbefore 6500 BC	11%6 of 56 copies read
First farmers6500 to 3000 BC	43%345 of 804 copies read
Bronze Age3000 to 1200 BC	39%255 of 657 copies read
Iron Age and Antiquity1200 BC to AD 600	34%329 of 961 copies read
Middle AgesAD 600 to 1500	35%168 of 481 copies read
Today1000 Genomes	36%367 of 1,006 copies

Neanderthal and Denisovan genomes

Altai Neanderthal: No copies
Vindija Neanderthal: No copies
Chagyrskaya Neanderthal: No copies
Denisovan: No copies

Neanderthals and Denisovans carried the other letter, so this letter is younger than our split with them.

For most ancient people only one of their two copies can be read, so these counts are copies read, not people. Close relatives, repeated samples and samples the archive marks as unreliable are left out. Damage in old DNA can fake this letter, so it is counted only from samples treated to remove that damage and from high-quality genomes. Ancient genomes from the Allen Ancient DNA Resource (AADR v66): 15,136 people.

rs1801133

The marker

Gene or region: MTHFR
Marker: rs1801133
Location: Chromosome 1 · GRCh37 11,856,378 · GRCh38 11,796,321
Letters studied: A and G, with A as the studied allele

A DNA Traits report reads this marker in your raw DNA file and shows which of the three genotypes is yours, with how common it is. It counts the copies of the studied allele; it does not measure the trait itself.

Marker: MTHFR · rs1801133
Location: Chromosome 1 · GRCh37 11,856,378 · GRCh38 11,796,321
Studied allele: A
Published statistic: Effect allele G (folate-raising): +0.096 Icelandic, +0.18 Inter99, +0.18 Health2006 on a quantile-normalised scale; combined P 9.5e-53, N 37,337; heterogeneity I² 62% (P 0.005); Table 2; 0.1 SD per copy (Table 2 (Icelandic column); sample size in the Results study outline)
1000 Genomes Project phase 3, people with 0, 1 and 2 copies: All regions 1480 / 819 / 205 · Africa 549 / 105 / 7 · The Americas 91 / 183 / 73 · East Asia 259 / 192 / 53 · Europe 204 / 231 / 68 · South Asia 377 / 108 / 4

See this card in the sample report

Limits

What it cannot tell you

This common variant is often described as MTHFR C677T on the gene strand; the forward genomic A allele corresponds to that T allele. Its effect depends partly on folate intake and fortification. It does not measure DNA methylation or imply that folic acid is unsuitable. Only the studied A/G allele pair is interpreted. It cannot tell you a current folate level, is not a test for deficiency and cannot choose a diet, supplement or dose.

Genetic Architecture of Vitamin B12 and Folate Levels Uncovered Applying Deeply Sequenced Large Datasets (Grarup et al., 2013)

The same topic

More in Nutrition & metabolism

Free, once per account

See your own two letters.

Upload the raw DNA file you already have. Your report reads this marker and every other card studied for you, each with its evidence and its limits.

See a sample report