MTHFR 2 Mutations Indications for Ordering Clinical Background

Methotrexate Sensitivity (MTHFR)
2 Mutations
Identifies patients who may experience intolerance
to antifolate medications such as methotrexate
Indications for Ordering
Clinical Background
Disease Overview
Methotrexate is an antimetabolite drug used in treatment
of cancer and autoimmune diseases. As a structural
analogue of folate, methotrexate interferes with folate
metabolism by inhibiting dihydrofolate reductase, which
leads to depletion of cellular folate. Supplementation
with folate or folinic acid (leucovorin) reduces the
efficacy and toxicity of methotrexate.
Methylenetetrahydrofolate reductase (MTHFR) is an
important enzyme in maintaining cellular folate pools,
and MTHFR gene variants associated with reduced
enzyme function and hyperhomocysteinemia may affect
methotrexate sensitivity and contribute to toxicity.
Adverse effects of methotrexate therapy may include
cardiovascular, neurological, dermatologic, hematologic,
hepatic, and gastrointestinal symptoms.
An association between MTHFR variants and
methotrexate toxicity supports dose adjustment and
limitation/discontinuation of therapy in affected
MTHFR mutations are associated with an increased
risk for arteriosclerotic coronary disease and
venous thrombosis. They may also contribute to the
pathophysiology of neural tube defects, cardiovascular
disease, and a variety of malignancies.
US allele frequency of C677T = 0.39 and A1298C =
The frequency of homozygotes for C677T or A1298C is
8–12 percent in most populations.
The common MTHFR mutations, C677T and A1298C,
produce reduced function enzymes with altered catalytic
activity and thermolability.
Homozygotes for C677T have about 30 percent of normal
MTHFR enzyme activity; heterozygotes for C677T have
approximately 60 percent normal activity.
The C677T mutation is associated with elevated plasma
homocysteine levels, whereas the A1298C mutation is
Clinical relevance is associated with homozygosity for
C677T or A1298C, and the compound heterozygous
state (C677T/ A1298C).
Identification of individuals at risk for methotrexate
sensitivity due to prolonged administration of methotrexate as
management for the following conditions:
Acute lymphoblastic leukemia (ALL)
Chronic myelogenic leukemia (CML)
Juvenile idiopathic arthritis
Rheumatoid arthritis
Immune disease
Optimization of therapy for individuals requiring methotrexate
or other folate antimetabolites, particularly when a family
history of intolerance to methotrexate exists.
Contraindication for Ordering
For assessment of homocysteine levels and risk for
arteriosclerotic coronary disease and venous thrombosis, refer
to Methylenetetrahydrofolate Reductase (MTHFR) 2 Mutations
(ARUP test # 0055655).
Negative: No mutations detected; genotype is consistent with
normal MTHFR enzyme activity.
Heterozygous C677T or A1298C: decreased enzyme
activity but no correlation with methotrexate intolerance
Homozygous C677T: associated with increased plasma
homocysteine levels and methotrexate intolerance;
dosing adjustments/discontinuation may be required
Homozygous A1298C: associated with decreased enzyme
activity and lower dose requirements for methotrexate
Compound heterozygote (C677T/ A1298C): associated
with increased plasma homocysteine levels and
methotrexate intolerance
Genotype should be interpreted with clinical information;
consultation with a clinical pharmacist is recommended.
Analysis of the common MTHFR mutations, C677T and
A1298C, by polymerase chain reaction and fluorescence
monitoring using hybridization probes.
Analytical sensitivity and specificity are >99 percent.
500 Chipeta Way, Salt Lake City, UT 84108 • (800) 522-2787 • (801) 583-2787 •
Specific genotype or haplotype-based dosing guidelines are
not currently available.
MTHFR mutations, other than C677T and A1298C, will not
be detected.
Testing will not determine haplotypes.
Mutations in other genes and non-genetic factors that may
affect drug sensitivity are not detected.
Rare diagnostic errors may occur due to primer-site
Chiusolo P, et al. Preponderance of methylenetetrahydrofolate
reductase C677T homozygosity among leukemia patients
intolerant to methotrexate. Ann Oncol 2002;13:1915–8.
Donnelly JG. Pharmacogenetics in cancer chemotherapy:
balancing toxicity and response. Ther Drug Monit 2004;
Krajinovic M, et al. Role of polymorphisms in MTHFR
and MTHFD1 genes in the outcome of childhood acute
lymphoblastic leukemia. Pharmacogenomics 2004;4:66–72.
Urano W, et al. Polymorphisms in the methylenetetrahydrofolate
reductase gene were associated with both the efficacy and the
toxicity of methotrexate used for the treatment of rheumatoid
arthritis, as evidenced by single locus and haplotype analyses.
Pharmacogenetics 2002;12:183–90.
Test Information
Methotrexate Sensitivity by MTHFR Genotyping
For specific collection, transport, and testing information, refer to the ARUP Web site at
For information on test selection, ordering, and interpretation, refer to ARUP Consult® at