MTHFR Gene: How to Check Your Status from Raw Data

Medical Disclaimer: This article is for educational purposes only and does not constitute medical advice. MTHFR variants are common genetic polymorphisms that do not guarantee any specific health outcome. Always consult a qualified healthcare provider before making changes to your diet, supplements, or medications based on genetic information.

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What Is the MTHFR Gene and Why It Matters

The MTHFR gene encodes the enzyme methylenetetrahydrofolate reductase, which plays a central role in folate metabolism and the methylation cycle. Methylation is a biochemical process that occurs billions of times per second throughout your body — it regulates gene expression, neurotransmitter synthesis, detoxification, and DNA repair.

When the MTHFR enzyme works suboptimally due to genetic variants, the conversion of folate into its active form (5-methyltetrahydrofolate, or 5-MTHF) becomes less efficient. This can affect homocysteine metabolism, since MTHFR-dependent methylation is required to convert homocysteine back into methionine. Elevated homocysteine has been associated with cardiovascular risk, neural tube defects, and cognitive changes — though the clinical significance of MTHFR variants alone remains debated among researchers.

Two variants in particular have attracted significant scientific attention: rs1801133 (also known as C677T) and rs1801131 (also known as A1298C). These are single nucleotide polymorphisms (SNPs) — positions in your DNA where a single letter differs from the reference sequence. Understanding which variants you carry requires looking at your raw genetic data.

The good news is that if you have tested with 23andMe, AncestryDNA, MyHeritage, or another direct-to-consumer (DTC) genetic testing service, this information is already in your raw data file. You do not need to retest. You just need to know where to look.

Understanding MTHFR SNPs: rs1801133 and rs1801131 Explained

Before diving into how to find your variants, it helps to understand what these SNPs actually represent at the molecular level.

rs1801133 (C677T)

This SNP is located on chromosome 1 at position 11856378 (GRCh38 coordinates). The reference allele is C (cytosine), and the variant allele is T (thymine). The notation "C677T" refers to the position in the MTHFR coding sequence where the change occurs — codon 677, changing alanine to valine.

The TT genotype is associated with a thermolabile enzyme — it loses activity at higher body temperatures more readily than the CC variant. In raw data files from DTC tests, this SNP typically appears as rs1801133, and the genotype will show two letters representing your two alleles (one from each chromosome).

rs1801131 (A1298C)

This SNP is located nearby on the same gene. The reference allele is A (adenine), and the variant allele is C (cytosine). At codon 1298, this changes glutamate to alanine.

The A1298C variant has a milder individual effect than C677T, but when someone carries one copy of each variant (compound heterozygous: CT at rs1801133 + AC at rs1801131), the combined effect on enzyme activity may be more significant than either variant alone.

What "Compound Heterozygous" Means

If your raw data shows CT for rs1801133 and AC for rs1801131, you are compound heterozygous. This means you carry one variant allele at each position, on different chromosomes. Some clinicians treat this similarly to the TT homozygous state for C677T in terms of functional implications, though evidence remains mixed. Understanding this requires reading both SNPs together, not in isolation.

How to Download Your Raw DNA Data

To check your MTHFR variants, you first need to download your raw genetic data file. The process differs by testing provider.

23andMe

1. Log in to your account at 23andme.com
2. Navigate to Settings (gear icon, top right)
3. Scroll to 23andMe Data and click View
4. Select Download Raw Data
5. Choose All DNA Raw Data and confirm with your password
6. You will receive a .txt file (tab-separated) compressed as .zip

Note: If you tested with 23andMe, you may find it useful to read about what to do with your 23andMe raw data given recent changes to the company.

AncestryDNA

1. Log in at ancestry.com
2. Click DNA in the top navigation
3. Go to Settings (gear icon next to your name)
4. Under Test Management, click Download Raw DNA Data
5. Confirm via email, then download the .zip file containing a .txt file

For more on extracting health insights from AncestryDNA data, see AncestryDNA raw data health insights.

MyHeritage

1. Log in and go to DNA → Manage DNA Kits
2. Click the three-dot menu next to your kit
3. Select Download Raw DNA Data
4. Verify via email and download the .csv or .txt file

Other Providers

Most DTC genetics companies provide raw data downloads. The file format varies but is typically tab-separated or comma-separated text, with columns for rsID, chromosome, position, and genotype.

Finding MTHFR Variants in Your Raw Data File

Once you have your raw data file downloaded and unzipped, you can search it directly. No special software is required for this step.

Method 1: Text Editor Search

Open the file in any text editor (Notepad on Windows, TextEdit on Mac, or a code editor like VS Code). Use Ctrl+F (Windows) or Cmd+F (Mac) to open the search bar.

Search for: rs1801133

The line will look something like this (format varies by provider):

rs1801133	1	11856378	AG

Or in 23andMe format:

rs1801133	1	11856378	CT

The last column is your genotype — two letters representing your two alleles.

Then search for: rs1801131

Method 2: Terminal / Command Line (Mac/Linux)

If you are comfortable with the command line, this is faster:

grep "rs1801133\|rs1801131" your_raw_data_file.txt

This returns both lines instantly, even in files with hundreds of thousands of SNPs.

Method 3: Spreadsheet

Open the file in Excel or Google Sheets. Use Ctrl+F to search for the rsIDs. Some providers format the data as a proper CSV, making it easy to sort by the rsID column.

Interpreting What You See

Once you find the lines, the genotype column tells you your alleles. Here is a quick reference:

For rs1801133 (C677T):

• CC = no variant (wild type)
• CT or TC = heterozygous (one variant copy)
• TT = homozygous variant

For rs1801131 (A1298C):

• AA = no variant (wild type)
• AC or CA = heterozygous (one variant copy)
• CC = homozygous variant

Note that some providers report the complementary strand, so you may see GG, GA, or AA for rs1801133 instead of CC, CT, TT. This is not an error — it is simply reporting the opposite strand. The SNP databases on ClinVar and dbSNP provide strand orientation details if you need to verify.

Using Third-Party Tools to Analyze MTHFR Data

If manually searching your raw data file feels tedious, several tools can automate the process and provide additional context.

Genetic Genie (Free)

Genetic Genie is a free tool specifically designed for methylation and detoxification analysis. Upload your raw data file, and it will generate a report highlighting MTHFR variants (rs1801133, rs1801131) along with other methylation-related SNPs such as MTRR, MTR, COMT, and VDR.

The output is a color-coded table showing your genotype at each position and whether it is considered a variant. This is useful for a quick overview, though the tool does not provide detailed clinical interpretation.

Promethease

Promethease cross-references your raw data against the SNPedia database to generate a comprehensive report on thousands of SNPs. For MTHFR specifically, it will show your genotypes for both rs1801133 and rs1801131 along with curated summaries of relevant research.

If you are new to Promethease, the guide on how to read a Promethease report provides a walkthrough of navigating the interface. For a broader comparison of analysis platforms, see Promethease alternatives in 2026.

SelfDecode

SelfDecode offers a dedicated MTHFR report that includes rs1801133 and rs1801131, along with polygenic scores for related traits such as homocysteine levels and folate metabolism efficiency. The platform aggregates multiple SNPs for a more nuanced picture than single-variant analysis. See SelfDecode vs Promethease vs Genetic Genie for a comparison.

AskMyDNA

AskMyDNA takes a different approach: rather than generating a static report, it lets you have a conversation with your raw data. Upload your genome file and then ask specific questions like "What are my MTHFR genotypes for rs1801133 and rs1801131?" or "Do I have the compound heterozygous combination?" The AI references your actual genetic data in real time, rather than returning pre-written paragraphs. You can start with 3 free questions, no credit card required, which is often enough to check your MTHFR status and ask a follow-up about what it means for folate supplementation.

What Your MTHFR Results Mean (and Don't Mean)

This is perhaps the most important section — because the clinical significance of MTHFR variants is frequently overstated in wellness communities and undersold in conventional medicine. The reality is nuanced.

What the Research Actually Shows

The strongest evidence for C677T (rs1801133 TT genotype) relates to:

• Neural tube defects: Maternal TT genotype is associated with moderately increased risk, which is why folate supplementation in pregnancy is especially relevant. The association is real but not deterministic. (NIH reference)
• Homocysteine levels: TT homozygotes tend to have higher fasting homocysteine, particularly when dietary folate is low. Supplementation with folate (especially methylfolate) typically normalizes levels.
• Cardiovascular risk: Earlier studies suggested elevated CVD risk from MTHFR variants, but large meta-analyses have been inconsistent. The European Heart Journal and other sources note that in populations with adequate folate fortification, the risk elevation is minimal.

What MTHFR variants do NOT reliably predict in current evidence:

• Depression or anxiety (despite widespread claims online)
• Autism spectrum disorder
• Chronic fatigue
• "Toxin buildup" or detoxification failure
• Most of the conditions listed on many wellness websites

The American College of Medical Genetics (ACMG) specifically advises against reflexive clinical testing for MTHFR variants, noting that results are often misinterpreted and lead to unnecessary treatment.

The Dietary Folate Connection

MTHFR enzyme activity is highly sensitive to folate status. Many people with TT genotype who eat folate-rich diets (dark leafy greens, legumes, fortified foods) have normal homocysteine levels and no measurable functional deficit. The genotype creates a vulnerability, not a certainty.

For those with TT or compound heterozygous status who do have elevated homocysteine, the primary interventions studied are:

• Methylfolate (5-MTHF): The active form of folate that bypasses the MTHFR enzyme entirely. Doses used in research range from 400mcg to 15mg depending on context.
• Vitamin B12 (methylcobalamin): Works synergistically with folate in the methylation cycle.
• Vitamin B6 (pyridoxal-5-phosphate): Involved in the transsulfuration pathway as an alternative homocysteine clearance route.

These interventions should be discussed with a healthcare provider, not self-prescribed based on genotype alone.

Homocysteine Testing: The Missing Piece

Knowing your MTHFR genotype tells you about your enzymatic potential — it does not tell you your actual methylation status. Homocysteine testing does.

A fasting plasma homocysteine test (a standard blood test, not genetic) reveals whether elevated homocysteine is actually present. Normal fasting levels are typically below 15 µmol/L, with optimal levels often cited as below 10 µmol/L. This test:

• Is widely available through standard clinical labs
• Costs approximately $20–60 without insurance in the US
• Gives you actionable information regardless of MTHFR genotype
• Can be repeated to monitor response to dietary or supplement interventions

If your MTHFR genotype shows TT or compound heterozygous status, getting a homocysteine test is a logical next step — not because the genotype guarantees elevated levels, but because it represents a reasonable risk factor worth checking directly.

Other biomarkers often measured alongside homocysteine in methylation workups include:

MTHFR, Pregnancy, and Prenatal Considerations

The intersection of MTHFR variants and pregnancy is where the clinical evidence is most consistent and most actionable. This section is particularly relevant for individuals who are pregnant or planning a pregnancy.

Neural Tube Defects

The C677T TT genotype (rs1801133) is associated with approximately 2x increased risk of neural tube defects (NTDs) such as spina bifida and anencephaly in the offspring, when maternal folate status is inadequate. This is one of the reasons population-level folate fortification of grain products was introduced in the US in 1998 — it dramatically reduced NTD rates across the population, including in carriers of MTHFR variants.

Current recommendations from major obstetric organizations advise that women with known MTHFR TT genotype or prior NTD-affected pregnancy consider higher-dose folate supplementation (typically 4–5 mg/day of folic acid, or equivalent methylfolate). This should be discussed with an obstetrician or maternal-fetal medicine specialist.

Folic Acid vs. Methylfolate in Pregnancy

One practical consideration for MTHFR TT carriers: standard prenatal vitamins contain folic acid (the synthetic, oxidized form), which requires MTHFR to convert to active 5-MTHF. Some practitioners recommend methylfolate-containing prenatal vitamins for TT carriers, since this bypasses the conversion step entirely. The evidence on whether this makes a clinical difference for most TT carriers with adequate dietary folate is not definitive, but the theoretical rationale is sound.

Recurrent Pregnancy Loss

Some studies have examined MTHFR variants in relation to recurrent miscarriage, with mixed results. The association is weaker than for NTDs, and ACOG does not recommend routine MTHFR testing for recurrent pregnancy loss. However, homocysteine testing is sometimes included in recurrent loss workups given its role in implantation and placental function.

If you are working through a history of pregnancy complications and have your raw genetic data available, tools like AskMyDNA can help you explore your specific variants and formulate informed questions to bring to your obstetrician.

Comparing MTHFR Analysis Across Testing Platforms

Not all DNA testing platforms cover MTHFR variants equally. Here is a comparison of how rs1801133 and rs1801131 are handled across common platforms:

For a broader overview of platforms that accept raw data uploads and provide health insights, see best DNA upload sites in 2026.

Chip Generation Considerations

23andMe has used multiple chip versions over the years. The v5 chip (current) covers both rs1801133 and rs1801131. Earlier v2 and v3 chips covered rs1801133 but not always rs1801131. If you tested before 2017 and cannot find rs1801131 in your raw data, this may be why — the SNP simply was not genotyped in that version.

If a particular SNP is missing from your raw data, it will show as "no call" or simply be absent from the file. This is different from having the wild-type genotype — an absent SNP means no data was collected for that position.

FAQ

Do I need to see a doctor to understand my MTHFR results?

You do not need a doctor to find your MTHFR genotype in your raw data — that is a straightforward lookup. However, interpreting what it means for your health is where professional guidance becomes valuable. A clinician can order homocysteine testing, review your full medical history, assess your dietary folate intake, and recommend appropriate interventions if needed. The genotype alone, viewed in isolation, is rarely sufficient for clinical decision-making.

Is the TT genotype for rs1801133 dangerous?

Not inherently. Approximately 10–15% of people of European ancestry carry the TT genotype, and the majority have no significant health problems related to it. The variant reduces enzyme efficiency, but many TT carriers maintain normal homocysteine levels through adequate dietary folate. The word "dangerous" is not warranted — "a factor worth monitoring" is more accurate.

Can I take methylfolate without testing first?

Many people with TT genotype take methylfolate supplements without any adverse effects. However, high-dose methylfolate can cause side effects in some individuals, particularly those with certain psychiatric conditions or those who have not identified other genetic factors affecting the methylation cycle (such as COMT variants). Starting with lower doses and monitoring response is generally prudent. Consult a healthcare provider before high-dose supplementation.

Does MTHFR affect everyone with the variant the same way?

No. Gene expression is influenced by numerous factors: dietary intake, other genetic variants (the methylation cycle involves dozens of enzymes and cofactors beyond MTHFR), gut microbiome composition, stress, environmental exposures, and more. Two people with identical MTHFR genotypes can have very different functional methylation status. This is why looking at your raw data gives you a starting point, not a final answer. You can explore how your specific combination of MTHFR and related variants interacts by uploading your data to a platform like AskMyDNA and asking targeted questions about your methylation-related SNPs — 3 free questions, no credit card needed.

What if rs1801131 is missing from my raw data file?

If you cannot find rs1801131 in your file, the most likely explanations are: (1) your testing chip version did not include that SNP, or (2) the SNP did not pass quality control thresholds and was excluded from your results. In either case, it does not mean you have the variant — it means the test did not return a result for that position. You can have this SNP specifically tested through a clinical lab if it is clinically relevant for your situation.

Is MTHFR testing covered by insurance?

Clinical MTHFR testing (ordered by a physician) may be covered by insurance in specific contexts, such as recurrent pregnancy loss or unexplained elevated homocysteine. However, coverage varies widely. Some insurers consider MTHFR testing "not medically necessary" in the absence of specific clinical indications. If you already have raw data from a DTC test, using that data is a cost-free alternative for obtaining the genotype, though it does not replace physician-ordered testing in a clinical context.

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Conclusion

Checking your MTHFR status from raw genetic data is one of the more straightforward things you can do with your DTC test results. The two key SNPs — rs1801133 (C677T) and rs1801131 (A1298C) — are included in all major consumer genetic tests, and finding them requires nothing more than a text search in your downloaded data file.

Understanding what you find requires more context. The TT genotype for rs1801133 and compound heterozygous combinations are real factors in folate metabolism and homocysteine regulation, but they are not diagnoses and they do not determine outcomes on their own. Dietary folate status, other genetic variants, and overall health context matter enormously.

The most useful next step after identifying your MTHFR genotypes is a fasting plasma homocysteine test — a standard, inexpensive blood test that tells you whether the enzymatic variants are translating into any measurable functional change. From there, a clinician can guide appropriate interventions if needed.

Your raw data is a resource. Learning to read it — starting with well-studied variants like MTHFR — is a practical way to engage with your own biology. The knowledge is accessible, and the tools to interpret it are better than ever.

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