This document addresses methylenetetrahydrofolate reductase (MTHFR) gene mutation testing (that is, two common MTHFR variants, polymorphisms C677T and A1298C) for the screening, diagnosis, and clinical management of a variety of diseases and disorders.
Investigational and Not Medically Necessary:
Methylenetetrahydrofolate reductase mutation testing is considered investigational and not medically necessary for all indications.
Methylenetetrahydrofolate reductase (MTHFR) is an enzyme that plays a role in the processing of amino acids, the building blocks of proteins, and is important for a chemical reaction involving forms of the B-vitamin folate (folic acid or vitamin B9). The MTHFR gene provides instructions for making the MTHFR enzyme. The MTHFR enzyme is thought to have a role in homocysteine metabolism; the mutation is reported to reduce MTHFR activity, resulting in hyperhomocysteinemia. Polymorphisms or common variants (C677T and A1298C) in the MTHFR gene have been associated with an increased risk of homocystinuria, and suggested as a possible risk factor for developing a variety of diseases and disorders. The potential associations between MTHFR genotype status and a number of medical complications have been evaluated using methodologies such as case-control and cohort study designs, Mendelian randomization, and meta-analysis.
The Genetics Home Reference website (GHR, 2016) states that at least 40 mutations in the MTHFR gene have been identified in persons with homocystinuria. Increased levels of homocysteine have been associated with an increased risk for arterial and venous thromboembolism (VTE) in persons with or without a personal or family history or recurrent VTE (for example, VTE while on oral contraceptive, family history of stroke, pulmonary embolism, and deep vein thrombosis [DVT] in first-degree relatives under age 50) and for women with an increased risk for obstetric complications of abnormal placenta vasculature (including VTE or DVT during pregnancy, fetal death after 10 weeks gestation, fetal growth retardation and/or preeclampsia, abruptio placentae, and stillbirth). Other MTHFR gene mutations have been associated with an increased risk of neural tube defects including anencephaly and spina bifida.
MTHFR mutation analysis has been explored for use in the screening, diagnosis, risk assessment, and clinical management of numerous diseases and disorders. The test provides direct detection of the MTHFR C677T and A1298C common variants for hereditary hypercoagulability by polymerase chain reaction-based assay (PCR) techniques (GHR, 2016), and is offered as a single test or as part of a thrombophilia panel which may include mutation testing for prothrombin G20210A (factor II) and factor V Leiden (Kujovich, 2014).
MTHFR mutation analysis has been used to evaluate the association between MTHFR 677C>T polymorphism as a potential biomarker for the risk of developing certain diseases and conditions such as cleft lip and palate. According to the American College of Medical Genetic and Genomics (ACMG) practice guideline on MTHFR polymorphism testing (Hickey, 2013), a modest positive association has been found between the MTHFR thermolabile polymorphism and various medical conditions including, but not limited to:
Several studies and meta-analyses have also evaluated MTHFR polymorphisms (C677T and A1298C) in association to drug toxicity when folate antagonists (such as, fluorouracil and methotrexate) are utilized for the treatment of cancer and rheumatoid arthritis.
Studies of MTHFR variants in individuals with these disorders have reported mixed results; associations are found in some studies, but not in others. It remains unclear how changes in the MTHFR gene impact these disorders (GHR, 2016).
MTHFR Testing for Inherited Thrombophilia, Cardiovascular Disease, and Recurrent Pregnancy Loss
Genetic testing for mutations associated with thrombophilia is available for the MTHFR gene and proposed for use in the following clinical scenarios:
The MTHFR gene has been widely studied for conditions such as hyperhomocysteinemia and thrombophilia, the latter in individuals with or without a personal history of VTE, in family members of individuals with thrombophilia, and in pregnant women. The clinical validity of testing for inherited thrombophilia is determined by the predictive ability of the test for future thromboembolic events, both in individuals with and without prior thromboembolization. The peer-reviewed published medical literature consists of studies in which individuals with and without the MTHFR mutation are followed for the development of thromboembolism.
The association of MTHFR mutations with arterial or venous thromboembolic disease is not definitive, with studies reporting mixed results. Two meta-analyses (Li, 2014b; Zhou, 2013), a prospective study (Supanc, 2014), and a case-control study (Russo, 2015) have shown some association between MTHFR mutations and thromboembolic disease. However, the overall evidence is lacking as to how these associations will impact treatment decisions and demonstrate a net health benefit.
Klerk and colleagues (2002) conducted a meta-analysis of individual participant data from case-control observational studies with data on the relationship of MTHFR 677C>T polymorphisms and risk of coronary heart disease. Data was obtained from 40 (34 published and 6 unpublished) observational studies involving a total of 11,162 cases and 12,758 controls. The authors reported that individuals with the MTHFR 677TT genotype had a significantly higher risk of coronary heart disease, however, this risk was “particularly in the setting of low folate status.” In individuals identified with hyperhomocysteinemia, adequate folic acid intake appears to reduce the impact of MTHFR variants. This observation further complicates any attributable risk of hyperhomocysteinemia to an increased risk of cerebrovascular, peripheral vascular, and coronary heart disease, and for venous thromboembolic disease.
In a large population-based case control study of 9231 subjects (MEGA study), Bezemer and colleagues (2007) reported no association was demonstrated between the MTHFR gene mutation and recurrent VTE. den Heijer and colleagues (2007) reported results of a randomized, double-blind, placebo-controlled trial that found no reduction in VTE associated with the treatment of hyperhomocysteinemia.
Naess and colleagues (2008) performed a study (HUNT 2) of homocysteine and MTHFR 677TT genotype and risk for venous thrombosis in the general population. This case-cohort study prospectively investigated whether elevated homocysteine levels measured in blood samples drawn before the event and the MTHFR gene polymorphism C677T were associated with subsequent first venous thrombosis. Over 2 years, blood samples were collected from 66,140 subjects; during the 7-year follow-up period, 505 venous thrombosis cases were identified. A total of 1458 age- and sex-matched subjects were selected as controls from the original cohort. The total plasma homocysteine (tHcy) and MTHFR genotype were measured in stored samples that were drawn a median of 33 months before the events. In men, the odds ratio was 2.17 (95% confidence interval [CI], 1.20-3.91) for levels above versus below the 95th percentile, but no association was found in women (odds ratio, 1.00). Stratification by age, predisposing risk factors, or time-to-event did not alter these results. The authors concluded that elevated homocysteine levels in the general population predicted subsequent first venous thrombosis in men but not in women, and the MTHFR 677TT genotype was not related to risk for venous thrombosis.
In a prospective cohort study of 90 children with confirmed VTE or arterial ischemic stroke (Joachim, 2013), neither the prevalence of hyperhomocysteinemia nor that of MTHFR variant was increased relative to reference values, and adverse thrombus outcomes were not definitively associated with either. The authors suggested that routine testing for MTHFR 677C>T genotype as part of a thrombophilia evaluation in children with incident thromboembolism is not warranted. Larger studies are needed to establish or refute a link between MTHFR variant and adverse outcomes.
Mahajerin and colleagues (2014) reported findings of a single center, retrospective cohort study exploring patterns of thrombophilia testing in children and adolescents (0-20 years of age) who presented with VTE. Eligible subjects had VTE confirmed by imaging and were evaluated for the presence of significant risk factors. A total of 392 subjects (239 inpatient and 153 outpatient) met the inclusion criteria. Thrombophilia testing (including MTHFR, Factor V Leiden, protein C and other antithrombin activity; antiphospholipid antibodies and plasminogen activator inhibitor-1 levels) was ordered in 310 of the 392 subjects (79%). Positive results were found in 37 subjects (12%). Thrombophilia rate differences between outpatient and inpatient cohorts did not reach statistical significance except for protein C deficiency, which was significantly higher in the outpatient group. In the inpatient group, the presence of a central venous line was significantly associated with not having tests done (p<0.0022). The study results demonstrated a low thrombophilia rate in both the inpatient and outpatient settings in children and adolescents with VTE. The authors concluded that the role of thrombophilia testing should be explored further in other pediatric subjects and noted that that the “presence or absence of thrombophilia rarely influences VTE management.”
Trifa and colleagues (2014) attempted to demonstrate a possible contribution of the factor V Leiden, prothrombin G20210A, and MTHFR 677C>T and 1298A>C mutations to thrombotic risk in a retrospective review of individuals with polycythemia vera and essential thrombocythemia. A total of 34 of 86 subjects with polycythemia vera (39.5 %) had major thrombosis and 22 of 95 subjects (23.1 %) with essential thrombocythemia had major thrombosis. On univariate and multivariate analysis of the entire cohort of subjects, only factor V Leiden mutation was significantly associated with both arterial and venous thrombosis.
According to the GHR (2016), “research indicates that individuals who have the 677C>T polymorphism on both copies of the MTHFR gene have an increased risk of developing vascular disease, including heart disease and stroke.” Khandanpour and colleagues (2009b) performed a case-control study and meta-analysis evaluating the association of MTHFR C677T polymorphisms with the incidence of peripheral artery disease. A total of 133 subjects with peripheral artery disease were compared to 457 healthy controls. The MTHFR C677T allele frequencies in the subjects with peripheral artery disease and controls were 0.37 and 0.33, and the odds ratios for the association of the 677T allele or TT genotype with peripheral artery disease were 1.18 (95% CI, 0.89, 1.58) and 1.99 (95% CI, 1.09, 3.63). Homozygotes for the MTHFR C677T mutation had higher concentrations of tHcy (odds ratio, 2.82; 95% CI, 1.03, 7.77) compared to homozygotes for the MTHFR 677CC genotype. A meta-analysis of nine studies (including the authors’ study) showed that being homozygous for the C677T allele was associated with an increased risk of peripheral artery disease (pooled odds ratio, 1.36; 95% CI, 1.09, 1.68). The authors cautioned that these findings need to be replicated in a wider range of settings and with larger sample sizes.
Guerzoni and colleagues (2009) evaluated the effect of the MTHFR C677T polymorphism on atherosclerosis development, angiogenesis, and homocysteine metabolism as risk factors for coronary artery disease. A total of 244 subjects were evaluated by coronary angiography, 144 subjects with coronary artery disease and 99 controls. Using a multivariate model to adjust for other risk factors for coronary artery disease, the MTHFR polymorphism did not show an association with the extension and/or severity of coronary artery disease. The MTHFR C677T polymorphism showed no direct association with hyperhomocysteinemia or increased mean plasma concentrations of homocysteine metabolism.
Mehlig and colleagues (2013) examined whether the association between plasma homocysteine and coronary heart disease is modified by the MTHFR 677C>T polymorphism. This meta-analysis evaluated data from two case-control studies: the Stockholm Heart Epidemiology Program (SHEEP) (first-time myocardial infarction) and the INTERGENE study (myocardial infarction and unstable angina). The tHcy was determined in a total of 1150 cases and 1753 controls. In SHEEP, the association between tHcy and myocardial infarction was observed in MTHFR 677C-homozygotes (odds ratio, 1.4; 95% CI, 1.2 to 1.6) and in heterozygotes (odds ratio, 1.3; 95% CI, 1.1 to 1.6) but not in T-homozygotes, independent of smoking, physical activity and obesity. An effect modification of similar size was observed in the smaller INTERGENE study, although it was not statistically significant. In summary, the authors stated this meta-analysis showed that the association between elevated tHcy and coronary heart disease was confined to carriers of the MTHFR 677C allele; however, how these results could influence the management of tHcy-lowering therapy and alter treatment plans is unknown.
Li and colleagues (2014b) performed a systematic review and meta-analysis to evaluate the role of tHcy and homozygosity for the thermolabile variant of the MTHFR C677T genotype in the risk of retinal vein occlusion. A review of 42 studies with 6445 participants concluded there was no evidence to suggest an association between homozygosity for the MTHFR C677T genotype and retinal vein occlusion.
Because thrombophilias have been implicated as a possible cause of recurrent pregnancy loss, researchers have investigated the relationship between MTHFR mutations and females with a history of obstetric complications. The peer-reviewed published medical literature reports inconsistent findings in the causal relationship of inherited thrombophilic disorders and recurrent early pregnancy loss. Kist and colleagues (2008) conducted a meta-analysis to evaluate the relationship between markers of thrombophilia (including MTHFR C677T, factor V Leiden, and prothrombin G20210A) and adverse pregnancy outcomes with respect to potential confounders across studies. The authors identified a total of 98 case-control studies with clear definitions of one or more of the candidate confounders including ethnicity (for example, Caucasian or non-Caucasian), severity of illness, and method of testing (functional testing and/or genetic testing). Adverse pregnancy outcomes measured included recurrent fetal loss, fetal growth restriction, preeclampsia and placental abruption. Severity of illness was described by: (a) trimester of recurrent fetal loss; (b) proteinuria level, blood pressure, and gestational age at delivery in preeclampsia; (c) gestational age at delivery, percentile of low birth weight, and any additional adverse outcomes in combination with fetal growth restriction; and (d) gestational age at delivery with placental abruption. A total of 19 articles were identified that confirmed a significant relationship between preeclampsia and MTHFR C677T homozygous (odds ratio, 1.54; 95% CI, 1.30-1.82). Of these 19 articles, 15 addressed the issue of ethnicity. Nine articles studying Caucasian subjects showed a strong relationship between preeclampsia and MTHFR C677T homozygous (odds ratio, 1.68; 95% CI, 1.37-2.07), while the relationship was not significant in Asian subjects (3 articles, odds ratio, 1.15; 95% CI, 0.76-1.74) and African subjects (3 articles; odds ratio, 1.53; 95% CI, 0.34-6.94). Six studies that used a blood pressure measurement of ≥ 160/110 mm Hg as a criterion to define preeclampsia showed a stronger relationship (odds ratio, 1.77; 95% CI, 1.32-2.38) than that in 13 articles that used a minimum blood pressure measurement of ≥ 140/90 mm Hg to define the diagnosis (odds ratio, 1.30; 95% CI, 1.06-1.58). Two articles used both definitions dividing their cases into mild and severe preeclampsia groups. A cofounder analysis could not be performed on the relationship of preeclampsia with MTHFR C677T homozygous, since all 17 articles used genotyping alone, rather than using the phenotype of hyperhomocysteinemia.
There is some evidence suggesting that loss of the fetus documented to have been alive at or beyond 10 weeks gestation is associated with thrombophilia; however, in a multicenter case-control study, Hefler and colleagues (2004) compared 94 women with late unexplained intrauterine fetal death to 94 healthy women with at least one uncomplicated full-term pregnancy and found no significant association between 12 common polymorphisms of thrombolic and vascular genes, including MTHFR C677T and A1298C mutations.
Coriu and colleagues (2014) retrospectively performed genetic analyses of 151 pregnant women from a single center with a history of complicated pregnancy (that is, maternal thrombosis and placental vascular pathology [intrauterine growth restriction, preeclampsia, recurrent pregnancy loss]) to detect mutations in MTHFR C677T/A1298C and other gene mutations. There was no positive association (odds ratio, 0.69; 95% CI, 0.28-1.7; p=0.416) between thrombosis and MTHFR C677T gene mutations. Also, no association was found between the presence of thrombosis and compound heterozygous MTHFR C677T/A1298C (odds ratio, 0.63; 95% CI, 0.23-1.7; p=0.36).
Silver and colleagues (2016) performed a secondary analysis of data from a population-based case-control study of stillbirths (the Stillbirth Collaborative Researcher Network) to determine, the clinical utility of MTHFR C677T testing for prothrombin-related thrombophilia. In addition to testing for MTHFR C677T and A1298C mutations, testing for FVL, prothrombin G20210A, and plasminogen activating inhibitor-1 4G/5G variants was performed on maternal and fetal (or placental) DNA from single pregnancies. There was an increased odds of stillbirth for maternal homozygous FVL variant. However, there were no significant differences in the odds of stillbirth for any other maternal thrombophilia, even after stratified analyses. The data did not support routine testing of MTHFR C677T and A1298C mutations for heritable thrombophilias as part of an evaluation for possible causes of stillbirth.
In 2014, the American College of Obstetricians and Gynecologists (ACOG) reaffirmed clinical management guidelines published in 2013 for inherited thrombophilias in pregnancy. These guidelines state that a definitive causal link cannot be made between inherited thrombophilias and adverse pregnancy outcomes. Screening for inherited thrombophilias is controversial, but may be considered for pregnant women in the following situations:
The guidelines also state:
The ACMG practice guideline (Hickey, 2013) on MTHFR polymorphism testing states:
MTHFR polymorphism testing is frequently ordered by physicians as part of the clinical evaluation for thrombophilia. It was previously hypothesized that reduced enzyme activity of MTHFR led to mild hyperhomocysteinemia which led to an increased risk for venous thromboembolism, coronary heart disease, and recurrent pregnancy loss. Recent meta-analyses have disproven an association between hyperhomocysteinemia and risk for coronary heart disease and between MTHFR polymorphism status and risk for venous thromboembolism. There is growing evidence that MTHFR polymorphism testing has minimal clinical utility and, therefore should not be ordered as a part of a routine evaluation for thrombophilia.
The National Society for Genetic Counselors (NSGC) (Laurino, 2005; reaffirmed 2010) provides recommendations for genetic evaluation and counseling of couples with recurrent miscarriage, defined as three or more clinically recognized consecutive or nonconsecutive pregnancy losses occurring prior to fetal viability (< 24 weeks gestation). The recommendations state that testing for thermolabile C677T MTHFR mutation is not justified (associated with some hereditary thrombophilia patterns such as hyperhomocysteinemia).
Duhl and colleagues (2007) published a consensus report and recommendation for prevention and treatment of venous thromboembolism and adverse pregnancy outcome. The authors acknowledged that “studies of the possible relationship between thrombophilia and pregnancy loss are plagued by differences in the definitions used for miscarriage and fetal death, and the methods used to select patients, and the lack of appropriate, ethnicity-matched controls.” Most research suggests that thrombophilias, including the most common MTHFR mutation, “are not associated with loss of the conceptus or recurrent miscarriage before 10 weeks’ gestation (preembryonic or embryonic losses).” The authors suggest that more evidenced-based data from prospective randomized trials evaluating the use of anticoagulation for the prevention of adverse pregnancy outcomes are needed before routine thrombophilia screening can be justified. For women with pregnancy loss after 10 weeks gestation, the panel recommended thrombophilia screening for individuals with unexplained fetal loss at 20 weeks gestation or longer; however, the basic screening tests did not include a recommendation for MTHFR mutation testing (Level IIIC evidence).
Inherited thrombophilias are a group of disorders that predispose to thrombosis. MTHFR mutation testing is available for these disorders and has been suggested to assist in the screening, diagnosis, and management of individuals predisposed to thrombosis. Genetic testing for mutations in the MTHFR gene for inherited thrombophilia is available, however, the clinical utility has not been established in any randomized controlled trials or controlled clinical trials in which testing for thrombophilia, including hyperhomocysteinemia, was the primary intervention and recurrent VTE was the outcome measure (Cohn, 2013). There is limited evidence on the clinical utility of testing for MTHFR mutations in persons with VTE or at risk for VTE. Given the lack of available evidence, and lack of clinical utility for serum homocysteine testing in general, it is unlikely that MTHFR mutation testing would alter the management of therapy resulting in improved clinical outcomes. At the current time, there is insufficient evidence in the peer-reviewed published medical literature and lack of support for MTHFR mutation testing from professional specialty society consensus guidelines establishing a definitive causal relationship between inherited thrombophilias and recurrent early pregnancy loss. The clinical utility of genetic testing for inherited thrombophilia disorders, including MTHFR mutation testing has not been established. The peer-reviewed published medical literature suggests MTHFR enzyme activity associated with hyperhomocysteinemia are not typically associated with pregnancy loss prior to 10 weeks gestation. Routine screening of all pregnant women is not recommended. Other evidence-based guidelines state the presence of inherited thrombophilia is an insignificant factor in determining the optimal duration of anticoagulation in individuals with venous thromboembolism. It is not possible to define a clinical situation in which the benefit of MTHFR mutation testing outweighs the risks of anticoagulation given the low risk of venous thromboembolism in some clinical situations. Additional studies are necessary to determine how MTHFR mutation testing impacts treatment decisions, and how these treatments improve health outcomes.
MTHFR Testing for Cancer Susceptibility
MTHFR genotype status has been associated with an increased risk of developing specific cancers (such as, acute lymphoblastic leukemia in children, and breast, cervical, colorectal, and ovarian cancers), and a decreased risk of developing other cancers (Hickey, 2013). MTHFR mutation analysis has been utilized in evaluating the association between MTHFR polymorphisms (C677T and A1298C) as potential biomarkers for cancer susceptibility. According to the ACGM practice guidelines (Hickey, 2013), the overall risk of developing specific cancers does not appear to be changed with MTHFR polymorphism testing (Zacho, 2011).
MTHFR Testing for Guiding Drug Therapy
Genotyping for MTHFR has been use to evaluate the therapeutic response of methotrexate in the treatment of rheumatoid arthritis and drug-related toxicity in antifolate chemotherapy (Fisher, 2009; Spyridopoulou, 2012). Two MTHFR polymorphisms, C677T and A1298C, influence metabolism of folates and have the potential to modify the pharmacodynamics of antifolates and other drugs whose metabolism, biochemical effects, or target structures require methylation reactions regulated by the MTHFR enzyme.
Lee and colleagues (2010) evaluated studies conducted on the association between MTHFR C677T and A1298C polymorphisms on the toxicity and efficacy of methotrexate in rheumatoid arthritis. A meta-analysis was then conducted to compare the toxicity and efficacy of methotrexate with respect to the MTHFR 677CC and 677CT/TT genotypes and MTHFR 1298AA and 1298AC/CC genotypes. The meta-analysis of eight studies including 1514 subjects did not demonstrate any association between the MTHFR C677T and A1298C polymorphisms and methotrexate toxicity when used in subjects with rheumatoid arthritis. The odds ratio for adverse effects with MTHFR 677CC versus 677CT/TT in all subjects was 0.633 (95% CI, 0.325, 1.234; p=0.180). The odds ratio for adverse effects with MTHFR 1298AA versus 1298AC/CC in all subjects was 0.942 (95% CI, 0.479, 1.851; p=0.861). In addition, no association was found between MTHFR C677T and A1298C polymorphisms and the efficacy of methotrexate in all subjects with rheumatoid arthritis.
Wang and colleagues (2012) performed a meta-analysis of 20 studies to examine genetic polymorphisms, including MTHFR variants, in predicting clinical outcomes (that is, response rates, overall survival, and toxicity) in individuals with gastric cancer treated with platinum/5-fluorouracil (5-FU)-based chemotherapy. No significant association was found between response rates and MTHFR polymorphisms. A significant association was demonstrated between toxicity and MTHFR polymorphism in specific studies. The authors concluded that studies with larger sample size using multivariate analysis are needed to give “more persuasive data” on the presumed association of MTHFR polymorphisms and predicting response to chemotherapy.
The Agency for Healthcare Research and Quality (AHRQ) (Raman, 2008) published a technology assessment reviewing use of pharmcogenetic tests for variants, including MTHFR, for non-cancer and cancer conditions. The report found that the evidence indicates MTHFR gene polymorphisms do not predict response to chemotherapy, concluding:
Overall, studies evaluating associations between the pharmacogenetic test results and the patient's response to therapy for non-cancer and cancer conditions showed considerable variation in study designs, study populations, medication dosages, and the type of medications. This variation warrants caution when interpreting our results. Data on the relationships among pharmacogenetic test results and patient- and disease-related factors and on the patient's response to therapy are limited. We found no data on the benefits, harms, or adverse effects from subsequent therapeutic management after pharmacogenetic testing. Detailed patient-level analyses are needed to adjust estimates for the effects of modifiers, such as age or tumor stage.
The ACMG practice guideline (Hickey, 2013) on testing for MTHFR genotype status states that individuals:
…should be counseled that it is important to provide their MTHFR genotype status to any physician who is considering starting them on types of chemotherapy whose activity depends on intracellular concentration of folate (e.g., methotrexate). In individuals who have a known thrombophilia, such as factor V Leiden or prothrombin c.*97G→A, most available studies support the contention that MTHFR genotype status does not alter their thrombotic risk to a clinically significant degree.
In summary, there is a paucity of evidence in the peer-reviewed published medical literature establishing the clinical utility of genotyping for MTHFR in guiding drug therapy for any indication.
MTHFR Testing for Neural Tube Defects
The MTHFR gene provides instructions for making the MTHFR enzyme which is important in a chemical reaction involving forms of the vitamin folate (vitamin B9) (GHR, 2016). Individuals with the common variant of the MTHFR gene, the 677C>T polymorphism, have elevated levels of homocysteine in their blood resulting from reduced activity of the MTHFR enzyme at higher temperatures (thermolabile). MTHFR gene polymorphisms are associated with an increased risk of the most common type of neural tube defect called anencephaly, a condition where the affected individual is missing large parts of the brain and is missing or has incompletely formed skull bones. These variations are common in many populations and most people with MTHFR gene polymorphisms do not have neural tube defects and their children are also unaffected. There is limited data regarding the clear association of MTHFR polymorphisms and how these variations increase the risk of neural tube defects and other complications of pregnancy related to the ability of the MTHFR enzyme to process folate (GHR, 2016). The available peer-reviewed published medical literature consists of observational studies and small case controlled and cohort studies of heterogeneous populations with reporting biases.
Yang and colleagues (2015) performed a meta-analysis of three groups of individuals with neural tube defects to investigate the association between the MTHFR C677T polymorphism and neural tube defect risks. A total of 40 articles were analyzed including tests for heterogeneity, sensitivity analysis, and assessment of publication bias. Thirteen studies compared 1329 persons with neural tube defects to 2965 healthy controls; 34 studies compared 3018 mothers with neural tube defect progeny to 8746 healthy controls; and, 3 studies compared 157 fathers with neural tube defect progeny to 705 healthy controls. The analysis results identified allele contrast in individuals with neural tube defects (odds ratio, 1.445; 95% CI, 1.186, 1.760); allele contrast in mothers (odds ratio, 1.342; 95% CI, 1.166, 1.544); and allele contrast in fathers (odds ratio, 1.062; 95% CI, 0.821, 1.374). The authors found no association between any of the father’s genotypes and neural tube defects, whereas a significant correlation between MTHFR C677T polymorphism and neural tube defect risk was found in persons with neural tube defects and in their mothers. Several limitations of this meta-analysis including the potential for selection bias as only studies in English or Chinese were selected and the number of studies and sample size in some subgroups was relatively small.
An ACGM practice guideline (Hickey, 2013) on the evidence for MTHFR polymorphism testing for neural tube defects states:
Because MTHFR polymorphism is only one of many factors contributing to the overall clinical picture, the utility of this testing is currently ambiguous. Furthermore, US-mandated fortification of grain products with folic acid to decrease the incidence of neural tube defects has resulted in increased serum folate concentrations and lowered serum total homocysteine levels in the general population. This public health initiative may be incidentally reducing some of the perceived risk associated with MTHFR polymorphisms. This is hypothesized to be one reason that an association between the “thermolabile” variant and venous thromboembolism is no longer observed in the North-American population.
MTHFR Testing for Other Medical Conditions
Polymorphisms in the MTHFR gene have been studied as possible risk factors for the development of other conditions including, but not limited to, Alzheimer’s disease, bone loss and fracture risk, diabetes, and glaucoma (Zacharaki, 2014).
Peng and colleagues (2015) performed a meta-analysis of 40 case-control studies including 4503 subjects with Alzheimer’s disease and 5767 controls. When data was pooled from all studies, a significant risk was found for Alzheimer’s disease. In subgroup analyses stratified by ethnicity, age of onset, and apolipoprotein E4 status, a significant increase in risk for Alzheimer’s disease was found in the Asian subjects, late-onset Alzheimer’s disease, and apolipoprotein E4 carriers. The authors suggested that MTHFR C677T polymorphism had a significant association with susceptibility for Alzheimer’s disease, although further investigation is warranted.
Zhu and colleagues (2009) evaluated 1213 women aged 70-85 and found that MTHFR C677T and A1298C polymorphisms were only weakly related to bone outcome measures but not fracture risk. Gjesdal and colleagues (2006) examined the association of hip bone marrow density with levels of tHcy, folate, and vitamin B12 and the MTHFR 677C>T and 1298A>C polymorphisms. Bone marrow density was measured in 2268 men and 3030 women from the Hordaland Homocysteine Study cohort. The authors observed no association between bone marrow density and vitamin B12 level or MTHFR polymorphisms.
Russo and colleagues (2011) evaluated the role of mild hyperhomocysteinemia and the MTHFR C677T polymorphism as a risk factor for long-term type 2 diabetes complications. In 216 of the subjects available at the time of follow-up evaluation (65 ± 9 months), the prevalence of MTHFR TT genotype was not associated with an increased incidence of macroangiopathy for those subjects with or without macroangiopathy at follow-up (17.1% vs. 26.9%; p>0.05). Both hyperhomocysteinemia and MTHFR TT genotype were insignificant risk factors for the onset of macrovascular disease, either at univariate or multivariate analysis, after adjusting for major determinants of tHcy levels, specifically identified in this population as well as for major cardiovascular risk factors. A test for sex-MTHFR genotype interaction on the risk for macroangiopathy was not significant (p>0.05 for the interaction term). The authors concluded that in this cohort of subjects with diabetes, mild hyperhomocysteinemia and the MTHFR TT genotype are not significant risk factors for the development of macroangiopathy.
Yigit and colleagues (2013) evaluated the possible association between MTHFR gene C677T mutation and diabetic peripheral neuropathy. A total of 230 subjects with diabetic peripheral neuropathy and 282 healthy controls were genotyped using the PCR-based polymorphism assay for the MTHFR gene C677T mutation. The genotype and allele frequencies of the MTHFR C677T mutation showed statistically significant differences between the subjects with diabetic peripheral neuropathy and the controls (p=0.003 and p=0.002, respectively). After subjects with diabetic peripheral neuropathy were stratified according to clinical and demographic characteristics, a significant association was observed between the MTHFR C677T mutation and history of retinopathy (p=0.039); however, the authors concluded that the significance of the MTHFR gene C677T mutation in diabetic peripheral neuropathy requires further study.
MTHFR Testing for Behavioral Health and Neuropsychiatric Disorders
Behavioral health and neuropsychiatric disorders encompass a wide range of conditions and disorders and are generally classified by symptomatology in systems such as the classification outlined in the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Genetic testing for mutations in the MTHFR gene in behavioral health disorders is primarily related to several clinical situations:
Several commercially available panels of genetic tests include the MTHFR gene and have been proposed for use in the diagnosis, risk assessment, and management of behavioral health and neuropsychiatric disorders. Genotyping of genes involved in these disorders can be accomplished by single nucleotide polymorphism microarrays, standard Sanger sequencing, or next-generation sequencing methods. There is currently a lack of information on the analytic validity of commercially available test panels. A search of the peer-reviewed published medical literature did not identify any studies that specifically evaluate the analytic validity of MTHFR testing methods performed for behavioral health and neuropsychiatric disorders.
Gatt and colleagues (2015) performed a review of meta-analysis studies examining the association between specific genes and specific behavioral health disorders. A total of 134 genes (206 variants) were identified as risk factors significantly associated with anxiety disorders, attention-deficit/hyperactivity disorder, major depressive disorder, bipolar disorder, or schizophrenia. Thirteen genetic variants, including the MTHFR C677T and MTHFR A1298C, were identified as shared between two or more disorders. The review highlighted “the progress that is being made in identifying shared and unique genetic mechanisms that contribute to the risk of developing several major psychiatric disorders.” However, additional research is needed to identify how this information would alter treatment plans and improve net health outcomes for persons with these conditions.
Hu and colleagues (2015) conducted a meta-analysis of 38 studies evaluating the association between MTHFR variants and risk of bipolar disorder or schizophrenia. The authors found a significant association between the MTHFR C677T variant and schizophrenia (odds ratio, 1.34; 95% CI, 1.18 to 1.53). A marginal association was found between MTHFR C677T with an increased risk of bipolar disorder (odds ratio, 26; 95% CI, 1.00 to 1.59). Subgroup analysis by ethnicity indicated that a significant association between MTHFR variants and schizophrenia and bipolar disorder existed in Asian and African American populations, but not in the Caucasian population.
Bousman and colleagues (2014) conducted a prospective cohort study to evaluate the association between MTHFR genetic variants and prognosis of major depressive disorder. A total of 147 primary care attendees with major depression underwent genotyping for two functional MTHFR polymorphisms (C677T [rs1801133] and A1298C [rs1801131]) and seven haplotype-tagging single nucleotide polymorphisms and serial measures of depression. Over a 5-year period, the MTHFR C677T polymorphism was significantly associated with symptom severity trajectory as measured by the Primary Care Evaluation of Mental Disorders Patient Health Questionnaire-9 (p=0.038). The MTHFR A1298C polymorphism and the haplotype-tagging single nucleotide polymorphisms were not associated with disease prognosis.
Wu and colleagues (2013) performed a meta-analysis of 26 published genome-wide association studies evaluating the association of MTHFR variants with depression. Low-strength associations were reported between numerous MTHFR single nucleotide polymorphisms and depression (odds ratio, 1.15 to 1.42). Subgroup analysis by ethnicity indicated a stronger association in Asian populations. In the Caucasian population, the associations were of marginal significance and in elderly individuals the associations were not statistically significant.
Lizer and colleagues (2011) conducted a case-control study of 156 subjects and found no significant differences in the frequency of various MTHFR C667T genotypes between depressed and nondepressed persons.
Peerbooms and colleagues (2011) conducted a systematic review and meta-analysis of case-control studies evaluating associations between the MTHFR single nucleotide polymorphisms C677T and A1298C and bipolar disorder (10 studies), unipolar depression (17 studies), and schizophrenia (24 studies). The MTHFR C677T single nucleotide polymorphism was significantly associated with all disorders combined (odds ratio, 1.26 comparing homozygotes; 95% CI, 1.09 to 1.46). The MTHFR A1298C single nucleotide polymorphism was significantly associated with bipolar disorder (odds ratio, 2.03 comparing homozygotes; 95% CI, 1.07 to 3.86).
In summary, the evidence on the clinical validity of genetic testing for evaluation of MTHFR polymorphisms of behavioral health and neuropsychiatric disorders consists primarily of genome-wide association studies and case-control studies that indicate a correlation between variants of these genes and clinical factors; although, the available evidence shows low-strength associations with a variety of behavioral health disorders. No studies of clinical validity were identified that evaluate defined groups of persons (such as, those with depression and nonresponse to SSRIs and those with schizophrenia) or report the sensitivity and specificity of panel results for those persons. Therefore, lacking clinical evidence, it is not possible to estimate the clinical sensitivity and specificity of MTHFR testing as a diagnostic test for specific groups of persons. In addition, a range of associations are reported for response to certain medications and alterations in pharmacokinetics. Evidence is lacking in the clinical utility of MTHFR testing for the management of behavioral health medications (such as anti-anxiety, antidepressants, and antipsychotic drugs), and how testing would impact the diagnostic work-up and treatment decisions that would improve health outcomes.
Genetic testing for polymorphisms (mutations) C677T and A1298C in the MTHFR gene has been explored for use in the diagnosis, risk assessment, and/or disease management of numerous clinical disorders. The MTHFR gene is a widely studied gene that codes for the protein that converts folic acid to methylfolate. Methylfolate is a precursor for the synthesis of norepinephrine, dopamine, and serotonin. It is a key step in the metabolism of homocysteine to methionine, and deficiency of MTHFR enzyme can result in hyperhomocysteinemia and homocystinuria. Hyperhomocysteinemia is implicated in a wide variety of disorders, including cardiovascular disease, VTE, and pregnancy complications (Khandanpour, 2009a; Said, 2010). The MTHFR protein also plays a major role in control of changes in gene function that do not involve changes in DNA sequences. The C677T polymorphism of the MTHFR gene is common in Western populations, with 10% to 15% of individuals being homozygous for this polymorphism. Other common polymorphisms of the MTHFR gene include A1286C and A1298C. These polymorphisms result in altered activity of the MTHFR enzyme. Several commercial laboratories offer genetic testing for the MTHFR gene as a single test or in test panels.
Thrombophilia (also known as hypercoagulability) leads to the inappropriate formation of blood clots. In adults, this disorder most commonly manifests as VTE, such as deep vein thrombosis (DVT) in the legs and pulmonary embolism (PE). In women, VTE may result in adverse pregnancy outcomes. It has been estimated that in the United States, approximately 300,000 to 600,000 individuals are affected by VTE annually.
The predisposition to form clots may be caused by genetic factors, acquired changes in the clotting mechanism, or, more commonly, an interaction between genetic and acquired factors. Independent environmental factors contributing to VTE include, but are not limited to: male sex, confinement to a nursing home or hospital, older age, smoking; trauma sufficient to require hospitalization, malignant neoplasm, neurologic disease with chronic extremity paresis, superficial vein thrombosis, and prior central venous catheter or transvenous pacemaker. Additional risks for women include pregnancy and use of oral contraceptives, tamoxifen, raloxifene and estrogen replacement therapy (Spector, 2005).
Genetic risk factors for VTE include:
Morbidity and mortality in individuals with thrombophilia are primarily the result of VTE and PE. The risk for thrombosis may be significantly increased in individuals with a combination of two or more risk factors for thrombosis. Any multiplicity of risk factors, whether acquired or hereditary, elevates the risk for thrombosis.
Analytical validity: The ability of a genetic test to accurately and reliably measure the genotype of interest; the technical performance of the test, in terms of accurately identifying the genetic markers to be measured.
Clinical utility: The ability of the test to alter patient management and improve clinical outcomes.
Clinical validity: The ability of a genetic test to predict or detect the associated phenotype or disorder.
Deep vein thrombosis (DVT): A blood clot in one of the deep veins of the body.
Gene polymorphism: A discontinuous genetic variation resulting in the occurrence of several different forms or types of individuals among the members of a single species. A discontinuous genetic variation divides the individuals of a population into two or more sharply distinct forms.
Homocysteine: A naturally occurring amino acid that, if present at a high level in the blood, can produce an increased risk of blood clots. This condition is known as hyperhomocysteinemia. It is believed that high blood levels of homocysteine can damage the lining of blood vessels. This damage is what can lead to blood clots.
Hyperhomocysteinemia: A condition where an individual may get blood clots in either the veins (for example, DVT and pulmonary embolism) or arteries (for example, stroke and heart attack). In addition to making people prone to blood clots, hyperhomocysteinemia may also increase the risk of specific birth defects and other disorders. Common causes of hyperhomocysteinemia include kidney disease, lack of B vitamins (such as folate, vitamin B12, and vitamin B6) in the diet, hypothyroidism, alcoholism, and certain medications.
Methylenetetrahydrofolate reductase (MTHFR): An enzyme (protein) that breaks down homocysteine. Deficiency of the MTHFR enzyme may cause hyperhomocysteinemia.
Mutation: A change in a gene from what is considered normal.
Neural tube defects: A group of birth defects that occur during the development of the brain and spinal cord.
Thermolabile: A substance which is subject to destruction, decomposition, or change in response to heat.
Thrombophilia: A blood coagulation abnormality that increases the risk of thrombosis; also known as hypercoagulability.
Thrombosis: The presence of blood clots in the blood vessels.
Venous thromboembolism (VTE): The formation of a blood clot in the veins.
The following codes for treatments and procedures applicable to this document are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.
When services are Investigational and Not Medically Necessary:
When the code describes a procedure indicated in the Position Statement section as investigational and not medically necessary.
MTHFR (5,10-methylenetetrahydrofolate reductase) (eg, hereditary hypercoagulability) gene analysis, common variants (eg, 677T, 1298C)
Peer Reviewed Publications:
Government Agency, Medical Society, and Other Authoritative Publications:
|Websites for Additional Information|
Invader® MTHFR 677
Invader MTHFR 1298
MTHFR (C677T) Mutation Analysis
MTHFR C677T/A1298C Analysis
MTHFR DNA Mutation Analysis
MTHFR Genetic Testing
MTHFR Thermolabile Variant DNA Analysis
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Medical Policy & Technology Assessment Committee (MPTAC) review. The document deader wording updated from “Current Effective Date” to “Publish Date.” Updated Rationale, Background, References, and Websites for Additional Information sections.
MPTAC review. Updated Description, Rationale, Background, References, and Websites for Additional Information sections.
MPTAC review. Initial document development.