23andMe MTHFR C677T marker
MTHFR rs1801133 in 23andMe raw data.
If you are searching a 23andMe raw DNA file for MTHFR C677T, the marker most people mean is rs1801133. GenoSight can help you check whether that marker is present, then keep interpretation cautious inside a broader educational Detox & Methylation report.
Start with marker coverage
Do this before interpreting the raw letters.
- Use the downloaded 23andMe raw genotype file, usually a zipped text file
- Search for rs1801133 in the raw-data text file or use a local marker checker
- Treat missing rs1801133 as a coverage issue, not proof that you do or do not have a variant
- Interpret C677T with A1298C, COMT, folate context, labs, symptoms, and clinician guidance
What to know before you search the file.
A raw-data search can answer a narrow coverage question. It cannot tell you, by itself, whether you have a methylation issue or need a supplement.
23andMe raw data is informational
23andMe says raw data has undergone general quality review, but only a subset of markers are individually validated and the data is not for medical or diagnostic use.
rs1801133 is one marker
rs1801133 is commonly discussed as MTHFR C677T. It is usually considered alongside MTHFR A1298C rs1801131 rather than as a standalone answer.
GenoSight separates detection from interpretation
The free checker can show whether rs1801133 appears in your file. A full report adds cautious methylation context without prescribing supplements.
Keep raw data inside its limits.
GenoSight is educational only. It can help you move from a raw marker lookup to a structured report, but medical decisions require clinical confirmation, labs, and a qualified professional.
23andMe raw data download
Explains raw-data access, informational-use limits, download timing, zipped text files, and third-party interpretation cautions.
23andMe raw-data technical details
Explains strand reporting, reference genome language, and uncalled variants shown as double dashes in downloaded raw data.
MedlinePlus MTHFR gene
Describes MTHFR and notes that C677T and 1298A>C are common studied polymorphisms while keeping medical context separate.
Next steps with a 23andMe file
Check rs1801133 locally
Use the browser-only checker to see whether the marker appears in your file without uploading it.
ContinueCompare rs1801131
Read the A1298C marker page so C677T is not interpreted in isolation.
ContinueRun Detox & Methylation
Use free signup credits or choose monthly to generate a broader educational report from a compatible raw file.
Continuers1801133 and 23andMe questions
Can I find rs1801133 in 23andMe raw DNA data?
Sometimes. 23andMe download format, lab pipeline, and no-call results can vary, so the right first step is checking whether your specific downloaded file contains rs1801133.
What does rs1801133 mean in MTHFR?
rs1801133 is commonly discussed as MTHFR C677T. A raw genotype is not a methylation test, diagnosis, or supplement instruction, and it should be interpreted with A1298C, COMT, folate context, labs, symptoms, and clinician guidance.
Why do my 23andMe MTHFR letters not match C/T examples?
Consumer raw files, SNPedia-style pages, and blog posts can use different strand conventions. C pairs with G and T pairs with A, so a raw rs1801133 call such as G/G may be the complement of a C/C-style example, and A/G may line up with C/T-style notation. For rs1801131, T/G can similarly appear where another source discusses A/C. GenoSight keeps marker detection, strand caveats, and interpretation separate so raw letters do not turn into overconfident health advice.
What if my 23andMe file does not show rs1801133?
That usually means the marker is missing, uncalled, or represented differently in that file. It does not prove anything clinically by itself.
Can GenoSight analyze my 23andMe file for MTHFR?
Yes, if it is a compatible 23andMe raw genotype file. GenoSight can run an educational Detox & Methylation report that frames MTHFR with COMT, folate context, caveats, and source notes.