Being A1298C homozygous means both copies of one folate-processing gene carry the same common spelling change, one inherited from each parent. It is a normal genetic variation shared by millions of people, not a diagnosis. The label often sounds more alarming than it is, because this is the milder of the two well-known MTHFR changes, and on its own it usually leaves blood chemistry looking normal.
What the A1298C Variant Actually Changes
MTHFR is the gene for an enzyme that turns folate from food into the active form your cells use. That active folate feeds a chemical tagging process cells rely on for DNA repair, gene control, making brain messengers and clearing homocysteine.1Clin Obstet Gynecol Reprod Med. What Does It Mean to Be A1298C Homozygous? The body has other routes to supply methyl groups, including choline and betaine from food, so the MTHFR enzyme is one source among several.
On a report, AA means no copies of the change, AC means one copy (heterozygous), and CC means two copies (homozygous). You have CC.
People with two copies of A1298C have about 60% of normal enzyme activity in white blood cells.2PubMed. A second genetic polymorphism in methylenetetrahydrofolate reductase (MTHFR) associated with decreased enzyme activity That figure is a lab measurement, not a reading of how you feel or function. It doesn’t mean 40% of your overall folate handling is lost, and a partial slowdown often changes nothing you can feel.
Your report likely lists the better-known C677T variant right alongside this one, which invites comparison. Unlike C677T, A1298C doesn’t make the enzyme fragile or heat-sensitive.3PubMed Central. Homocysteine Metabolism Gene Polymorphisms (MTHFR C677T, MTHFR A1298C, MTR A2756G and MTRR A66G) Jointly Elevate the Risk of Folate Deficiency C677T is the one more closely tied to raised homocysteine, so reading CC on A1298C is not the same as reading TT on C677T. Several studies find A1298C doesn’t lower blood folate, and one found carriers had slightly higher folate.4PubMed Central. Homocysteine Metabolism Gene Polymorphisms (MTHFR C677T, MTHFR A1298C, MTR A2756G and MTRR A66G) Jointly Elevate the Risk of Folate Deficiency
Does It Raise Homocysteine or Clot and Heart Risk
Homocysteine is an amino acid in your blood, and high levels are linked to heart disease and clots. Your body makes it when it processes methionine from protein, then normally recycles it using folate, B12 and B6. If the recycling slows enough, homocysteine builds up.
For two copies of A1298C, usually it doesn’t. People with two copies did not have raised homocysteine in a large nutrition study.5PubMed. A common mutation A1298C in human methylenetetrahydrofolate reductase gene: association with plasma total homocysteine and folate concentrations In older British men and women, A1298C had no effect on homocysteine, folate or B12.6PubMed. The effect of the C677T and A1298C polymorphisms in the methylenetetrahydrofolate reductase gene on homocysteine levels in elderly men and women from the British regional heart study One study in India did link A1298C to higher homocysteine, though vegetarian diets low in B12 also raised it.7Journal of Human Genetics. Homocysteine levels are associated with MTHFR A1298C polymorphism in Indian population Diet may matter more than the gene, and homocysteine tends to rise only when A1298C is paired with C677T.8Journal of Clinical & Medical Genomics. Epigenetics in Clinical Practice: Characterizing Patient and Provider Experiences with MTHFR Polymorphisms and Methylfolate
A blood test can tell you what the gene can’t. The gene shows what you inherited; homocysteine shows what is happening now, and a normal level means the variant isn’t causing a measurable problem. If you’re worried, ask your doctor whether the test makes sense for you.
On clots, very large European data found A1298C raised clot risk by about 3%, roughly 30 times weaker than the known clotting gene Factor V Leiden.9PubMed Central. Association of MTHFR missense variants with thromboembolic diseases and coagulation factor levels in European populations Clots usually come from a mix of causes such as long immobility, surgery, hormones, smoking and family history, and this variant is a minor part of that mix. It showed no link to heart attacks or strokes in the same data.10PubMed Central. Association of MTHFR missense variants with thromboembolic diseases and coagulation factor levels in European populations One clot study found no genotype differences between patients and healthy people.11PubMed Central. Polymorphisms C677T and A1298C of MTHFR Gene: Homocysteine Levels and Prothrombotic Biomarkers in Coronary and Pulmonary Thromboembolic Disease A small Iranian study linked A1298C to coronary disease, while one copy looked protective.12Turkish Journal of Biochemistry. The association of methylene tetrahydrofolate reductase (MTHFR) A1298C gene polymorphism, homocysteine, vitamin B12, and folate with coronary artery disease (CAD) in the north of Iran The heart findings point in different directions, and none show a meaningful risk from two copies alone.
Pregnancy, Miscarriage and Fertility
Pooled data found no link between A1298C and repeated miscarriage.13PubMed. The association between maternal methylenetetrahydrofolate reductase C677T and A1298C polymorphism and birth defects and adverse pregnancy outcomes Unlike C677T, A1298C wasn’t linked to spinal birth defects or Down syndrome.14PubMed. The association between maternal methylenetetrahydrofolate reductase C677T and A1298C polymorphism and birth defects and adverse pregnancy outcomes An A1298C result alone doesn’t explain past losses.
You may still see MTHFR on your report after a loss because it was once commonly bundled into clotting and miscarriage panels. Other causes, such as chromosome changes in the embryo, are more common and are a better thing to discuss with your clinician.
Standard folic acid before pregnancy is still recommended for everyone planning one. It lowers the chance of neural tube defects, applies regardless of genotype, and a CC result is no reason to skip it or delay starting. You may run into claims that methylfolate prevents miscarriage in MTHFR carriers. One small study reported far fewer losses than with regular folic acid, but it mixed variant types and was a single trial, so it can’t settle the question. Don’t stop prescribed folic acid, and discuss any switch with your obstetrician.
For male fertility, the picture is mixed. One study found two copies more often in men with very low sperm counts.15PubMed Central. Association of the MTHFR A1298C Variant with Unexplained Severe Male Infertility One pooled analysis found no overall link, only a small rise in Asian men.16PubMed. Association between MTHFR A1298C polymorphism and male infertility: A meta-analysis Another found a small overall link, mostly with no sperm at all.17PubMed. Association of the methylenetetrahydrofolate reductase gene A1298C polymorphism with male infertility: a meta-analysis The variant may nudge risk slightly, but it isn’t a cause of infertility by itself. At a fertility appointment, mention the result, but fertility workups don’t usually change because of A1298C.
When You Also Carry C677T
Carrying one A1298C copy and one C677T copy is called compound heterozygous.18PubMed Central. Study of the C677T and 1298AC polymorphic genotypes of MTHFR Gene in autism spectrum disorder That pairing lowers enzyme activity by 50 to 60%.19PubMed Central. Study of the C677T and 1298AC polymorphic genotypes of MTHFR Gene in autism spectrum disorder The two variants lower activity in different ways, so together their effects add up. Even then, the lower activity matters mainly if folate or B12 intake is also low.
About 15 to 20% of people have this combination,20Journal of Clinical & Medical Genomics. Epigenetics in Clinical Practice: Characterizing Patient and Provider Experiences with MTHFR Polymorphisms and Methylfolate so it is a common pattern, not a rare finding. People with two A1298C copies plus C677T copies are very rare; one large Indian survey found no one with four changed copies.21PubMed. Spectrum of MTHFR gene SNPs C677T and A1298C: a study among 23 population groups of India
That affects how you read your report. CC at A1298C usually comes with no change at C677T, which reports typically list as CC. If C677T shows CT or TT, the combined picture matters more than either result alone. A homocysteine test tells you whether the pairing is having any effect, and it is most reasonable to check if you have other reasons for concern, such as clots or a family history.
Migraines, Mood and Other Claimed Links
Pooled data across five studies found two copies linked to migraine, mainly migraine without aura.22PubMed. Effects of MTHFR C677T and A1298C Polymorphisms on Migraine Susceptibility: A Meta-Analysis of 26 Studies Small single studies reported larger effects, but small studies often overstate risk. Carrying CC may slightly raise migraine odds, yet most carriers never have migraines. Sleep, stress, hormones, diet and strong family patterns matter as much.
One pooled analysis linked two copies to roughly 2.6 times higher odds of depression.23PubMed Central. Association between variants of MTHFR genes and psychiatric disorders: A meta-analysis Depression has many causes, including life events, sleep, illness and family history. Low mood deserves care on its own terms and shouldn’t be blamed on, or dismissed because of, a gene report.
In one study, the pairing of one copy of each variant was more common in autistic children.24Journal of American Physicians and Surgeons. Association of MTHFR Gene Variants with Autism That is a pattern in a group, not a cause in any one person. A genetic report shouldn’t be read as explaining or predicting a child’s development.
A1298C isn’t linked to colorectal cancer risk.25PubMed. Association of polymorphisms MTHFR C677T and A1298C with risk of colorectal cancer, genetic and epigenetic characteristic of tumors, and response to chemotherapy For methotrexate, an arthritis drug, studies disagree on whether CC changes side effects.26PubMed. Association of the MTHFR C677T and A1298C polymorphisms with methotrexate toxicity in rheumatoid arthritis: a meta-analysis If you take methotrexate, standard folic acid and blood monitoring still apply regardless of your result.
Do You Need Methylfolate or Special Supplements
Low folate and low B12 both go with higher homocysteine regardless of MTHFR type.27PubMed Central. Association of MTHFR polymorphism, folic acid, and vitamin B12 with serum homocysteine levels in pregnant women Low riboflavin (vitamin B2) is linked to higher homocysteine in everyone, not just variant carriers.28PubMed. Effect of riboflavin status on the homocysteine-lowering effect of folate in relation to the MTHFR (C677T) genotype A folate-rich diet and folic acid lower homocysteine across genotypes.29PubMed Central. Homocysteine Lowering by Folate-Rich Diet or Pharmacological Supplementations in Subjects with Moderate Hyperhomocysteinemia Covering these vitamins through food or a standard multivitamin is the most useful step.
Leafy greens, beans and fortified grains supply folate. Meat, eggs, dairy or fortified foods supply B12. Dairy, eggs and almonds supply riboflavin. A regular multivitamin typically covers all three at modest doses, and it is a simple, inexpensive option compared with specialty products, especially if your diet is uneven.
Folic acid is the form used in supplements and fortified foods, and the body converts it to the active form in several steps. Methylfolate is already the active form, which is why it is sold as an MTHFR fix. Because A1298C usually leaves folate and homocysteine normal, there is no good evidence that the conversion step is a problem methylfolate would solve, and most carriers have no proven need for it.
Vegetarians and vegans should make sure they get B12, since low B12 raised homocysteine in one population.30Journal of Human Genetics. Homocysteine levels are associated with MTHFR A1298C polymorphism in Indian population Before buying expensive supplements, ask whether your homocysteine is even high. High doses of folic acid aren’t better and can mask B12 deficiency. Tell your doctor about any supplement you start.
Why Doctors Don’t Routinely Test or Treat It
The American College of Medical Genetics and Genomics says there’s not enough evidence to support MTHFR variant testing.31Genetics in Medicine. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing US obstetricians’ groups don’t recommend MTHFR or homocysteine testing to explain blood clots.32Genetics in Medicine. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing British blood-disorder guidelines leave MTHFR out of inherited clotting tests.33Genetics in Medicine. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing Measuring homocysteine is more useful than knowing your genotype.34Genetics in Medicine. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing
Testing is only useful if the result changes what a doctor would do, and for A1298C it doesn’t change treatment. Homocysteine reflects the combined effect of your genes, your diet and your vitamin levels, so it shows what is actually happening. If it is normal, your genotype isn’t causing a problem. If it is high, the cause is more likely a vitamin shortfall that can be checked and corrected.
About 3 to 10% of Americans have two copies, and about a third have one.35Journal of Clinical & Medical Genomics. Epigenetics in Clinical Practice: Characterizing Patient and Provider Experiences with MTHFR Polymorphisms and Methylfolate The C version is far more common in parts of Asia, up to 70% of gene copies, and rarer in the Americas.36PubMed Central. Geographical Distribution of MTHFR C677T, A1298C and MTRR A66G Gene Polymorphisms in China: Findings from 15357 Adults of Han Nationality
When you talk to your doctor, expect them to say no treatment is needed for CC alone. Ask for a homocysteine test if you have clots, heart disease or a family history of either. Share any C677T result too, since the pairing matters. Don’t make medication changes based on the gene report.