MTHFR Mutations Indications for Ordering

Methylenetetrahydrofolate Reductase (MTHFR) 2
Mutations
Indications for Ordering
• Determine genetic cause for early-onset
hyperhomocysteinemia
• Predict methotrexate sensitivity which may be associated
with
o Toxicity in individuals with a family history of
intolerance
o Individuals taking prolonged administration of
methotrexate therapy (eg, ALL, CML, rheumatoid
arthritis)
• Limited utility
o For identification of early onset arteriosclerotic vascular
disease
o In determining risk for deep vein thrombosis (DVT)
• Not recommended testing for women who have
o Pregnancy complications
o Recurrent miscarriages
o A previous child with a neural tube defect (NTD)
Test Description
• PCR followed by fluorescence monitoring
• Hybridization probes detect c.665C>T; p.Ala222Val and
c.1286A>C; p.Glu429Ala (previously known as c.677C>T
and c.1298A>C, respectively)
Tests to Consider
Primary test
Methylenetetrahydrofolate Reductase (MTHFR) 2 Mutations
0055655
• To determine potential sensitivity to antifolate
medications and genetic cause for early-onset
hyperhomocysteinemia
Related tests
Homocysteine, Total 0099869
• Acceptable screening test for disorders of methionine
metabolism (congenital hyperhomocysteinemia)
• Not recommended for risk assessment of cardiovascular
disease or venous thromboembolism
Methotrexate, Sensitive 2005405
• Monitor methotrexate concentration in rheumatoid
arthritis
Thrombotic Risk, DNA Panel 0056200
• Acceptable panel to detect the 2 most common inherited
thrombophilias
Disease Overview
Prevalence – most common inherited risk factor for
hyperhomocysteinemia
• Allelic frequency (based on data from dbSNP, February
2013)
o c.665C>T − 0.35 in European Caucasians, 0.12 in African
Americans
o c.1286A>C − 0.31 in European Caucasians, 0.15 in
African Americans
• Homozygosity for c.665C>T is 1-15% in the United States
Related conditions
Hyperhomocysteinemia
• Moderately elevated plasma homocysteine
o Independent risk factor for atherosclerotic vascular
disease and venous thrombosis
▪ 10% of total risk may be attributable to elevated
plasma homocysteine
▪ For each 5 μmol/L homocysteine elevation, risk of
coronary artery disease increased by 60% for men and
80% for women
o Affected by genetic and environmental factors (eg,
dietary)
o Folic acid supplementation reduces homocysteine
levels, but effect on atherosclerosis and thrombosis risk
is not clearly defined
o Genetic testing is generally not useful for preventing or
predicting atherosclerosis
NTDs
• Defects in folate metabolism may play a role in NTDs but
risk is largely dependent on nutritional status and
homocysteine level
Thrombophilia
• MTHFR mutations − may interact with other inherited risk
factors for thrombosis (eg, factor V Leiden)
o Co-inheritance does not further increase the thrombotic
risk associated with factor V Leiden
FEBRUARY 2014 | © 2013 ARUP LABORATORIES | ARUP is a nonprofit enterprise of the University of Utah and its Department of Pathology.
500 Chipeta Way, Salt Lake City, UT 84108 | (800) 522-2787 | (801) 583-2787 | www.aruplab.com | www.arupconsult.com
Methotrexate sensitivity
• MTHFR mutations − associated with methotrexate toxicity
o Dose adjustment or discontinuation of therapy may be
advised for individuals with high-risk MTHFR genotypes
Pregnancy loss
• MTHFR mutations − not associated with recurrent
pregnancy loss
o Conflicting evidence regarding role in pregnancy
complications (eg, pre-eclampsia, placental abruption,
intrauterine growth restriction)
Genetics
Gene – MTHFR
Inheritance – autosomal recessive
Structure/function − MTHFR mutations (c.665C>T and
c.1286A>C) correlate with reduced MTHFR enzyme activity
• MTHFR enzyme is involved in folate metabolism
o Catalyzes 5,10-methylenetetrahydrofolate to 5methyltetrahydrofolate
o Necessary cofactor for the re-methylation of
homocysteine
o Reduced enzyme function increases plasma
homocysteine
Test Interpretation
Sensitivity/specificity
• Clinical sensitivity – undefined; dependent upon multiple
contributing factors
• Analytical sensitivity/specificity – 99%
Results
• Negative – no mutations detected
o Normal MTHFR enzyme activity expected
• Positive
o Homozygosity for c.665C>T
▪ Associated with increased plasma homocysteine levels
and increased risk for arteriosclerotic coronary disease
and venous thrombosis
▪ At risk for methotrexate intolerance and may require
dosing adjustments/discontinuation
o Homozygosity for c.1286A>C
▪ Associated with intermediate enzyme activity, but not
with increased plasma homocysteine levels
▪ No increased risk for premature cardiovascular
disease/venous thrombosis
▪ May require lower dose requirements for
methotrexate
o Compound heterozygosity (c.665C>T/c.1286A>C)
▪ Associated with increased plasma homocysteine levels
and increased risk for arteriosclerotic coronary disease
and venous thrombosis
▪ At risk for methotrexate intolerance and may require
dosing adjustments/discontinuation
o Heterozygosity for either c.665C>T or c.1286A>C
▪ Associated with intermediate levels of enzyme activity,
but NOT with increased plasma homocysteine levels
▪ No increased risk for premature cardiovascular
disease/venous thrombosis or methotrexate
intolerance
• Genotypes should be interpreted with clinical information
o Specific genotype- or haplotype-based methotrexate
dosing guidelines are not currently available
▪ Consultation with a clinical pharmacist is
recommended
Limitations
• MTHFR mutations other than c.665C>T and c.1286A>C are
not evaluated by this test
• Rare diagnostic errors may occur due to primer-site
mutations
FEBRUARY 2014 | © 2013 ARUP LABORATORIES