Mild hyperhomocysteinemia is an established risk factor for venous thromboembolic disease as well as cardiovascular disease. Methylenetetrahydrofolate reductase (MTHFR) is a regulatory enzyme in folate-dependent homocysteine remethylation, catalyzing the reduction of 5, 10-methylenetrahydrofolate to 5-methytetrahydrofolate. A common polymorphism in the MTHFR gene (Cè T at nucleotide position 677, resulting in substitution of valine for alanine) associated with a thermolabile enzyme and decreased specific MTHFR activity. The prevalence of the homozygous form ranges from 8% to 18% in various populations, but is very uncommon in individuals of African descent.

Clinically, homozygosity for this MTHFR polymorphism is associated with an increased risk for venous thromboembolism as well as premature vascular disease. It is possible to modulate this risk, however, by supplementing dietary folate and/or pyridoxine, which is associated with decreased homocysteine levels. Consequently, patients with elevated plasma homocysteine levels should be evaluated for the thermolabile MTHFR polymorphism, since this information is useful in determining an individual patient’s therapeutic regimen as well as for genetic counseling of the patient and their family members.

• The increased risk of thrombophilia associated with cardiovascular disease in homozygous methylenetetrahydrofolate reductase mutation patients is approximately 3-fold.
• Elevated homocysteine level is a risk factor for cardiovascular disease.
• Patients homozygous for the methylenetetrahydrofolate reductase polymorphism are at increased risk for elevated homocysteine levels if they are also folate or pyridoxine deficient.
• The risk of thrombosis is substantially increased for patients with multiple genetic risk factors (i.e. The "double hit hypothesis") including the methylenetetrahydrofolate reductase (MTHFR) polymorphism, Prothrombin (G20210A) gene polymorphism, factor V Leiden polymorphism, hyperhomocysteinemia, protein C deficiency, protein S deficiency and the antiphospholipid antibody syndrome(s).
• The PCR method is the only method available to accurately define genotype and determine heterozygosity versus homozygosity of patients with the thermolabile variant of the MTHFR gene.
• Definition and confirmation of the MTHFR mutation is necessary for genetic counseling of patients for themselves and family members.

Methylenetetrahydrofolate reductase (MTHFR) mutation by Polymerase Chain Reaction (PCR)

This assay utilizes genomic DNA isolated from the buffy coat to determine the genotype of the patient. The extracted DNA is then combined with specific oligonucleotide primers, deoxynucleotides, and Taq polymerase. The PCR products are then restricted using the enzyme HinFI to produce the DNA segment for analysis. The DNA is then analyzed by agarose gel electrophoreses and compared to restricted samples from a normal individual and an individual who is homozygous for the methylenetetrahydrofolate reductase (MTHFR) mutation.

CPT Codes: 83890, 83892, 83894, 83898, 83192

Methylenetetrahydrofolate reductase (MTHFR) Mutation:

Specimen Requirements: Whole Blood (EDTA or 3.2% Sodium Citrate)

Transport temperature: Ambient (22 - 24° C)

Specimen Stability: 7 days at 22 - 24° C

Assay Setup days: Tuesday

Assay Time: 2-4 days

Report Turn-around-Time: 1 week (via Fax)

Note: It is recommended that a separate plasma sample be sent to correlate the MTHFR DNA analysis with a homocsyteine level from the same collection time. The specimen requirements and shipping instructions for the homocysteine level are as follows:

Homocysteine Level:

Specimen Requirements: Plasma (3.2% Sodium Citrate)

Transport temperature: Frozen (-20 to -80° C)

Specimen Stability: 6 months at -20 to -80° C

Assay Setup days: Wednesday

Assay Time: 1 day

Report Turn-around-Time: 1 week (via Fax)

Call (800) 441-1416 or (919) 684-6366 to request shipping instructions, test requisitions, collection requirements, and additional information.

Activated Protein C (APC) Resistance - aPTT-Based

Activated Protein C (APC) Resistance - PT-Based

Anticardiolipin Antibodies (IgG, IgM, IgA)

Antithrombin III Activity

Factor II Assay (Functional)

Factor V Leiden Mutation (FV^R506Q)

Homocysteine Level

Lupus Anticoagulant Panel

Plasminogen Activity

Protein C Functional Assay

Protein S Functional Assay

Prothrombin (G20210A) Gene Mutation

Prothrombin (Factor II) Antigen

Thrombosis Panel

 

 

Previous Section - PCR ASSAYS

 

Last Modified: May 4, 2000