Tuesday, November 8, 2022

Homocysteinaemia (C677T, A128C-MTHFR) screening, total blood

Reference values Modification

Test code: 2743

Effective update from 23/11/2022


Mutations C677T and A1298C MTHFR gene are not detected.
Interpretive Data:

The 677T and A1298C mutations in the heterozygous or homozygous states correlate with reduced enzyme activity.

But only individuals homozygous for the C677T mutation or compound heterozygous for the C667T/A1298C mutations have significantly elevated plasma homocysteine levels.

Homozygosity for the C677T mutation (from 1.5 to 15% of the population) is associated with intermediate and mild hyperhomocystinemia and a threefold increased risk for premature cardiovascular disease.

Version of Test: 7

The C677T and A1298C variants decrease the enzymatic activity of the methylenetetrahydrofolate reductase (MTHFR), which indeed is a risk factor of hyperhomocysteinemia. High homocysteine ​​levels in blood may increase the risk of developing vascular disease, thrombosis or hypertension.


No risk of hyperhomocysteinemia has been demonstrated in individuals with these genotypes: heterozygous A1298C, heterozygous C677T, compound heterozygous A1298C / C677T, or homozygous A1298C. However, homozygous C677T patients are at moderately risk, so it is recommended to study fasting total plasma homocysteine (if not previously ordered, to provide more accurate counseling).


Clinical practice guidelines recommend not testing MTHFR polymorphisms as a part of a routine evaluation for thrombophilia since there is not enough scientific evidence to relate them to this phenotype (1).

This report must be interpreted by a specialist within the clinical context and family history of the patient, in conjunction with other laboratory findings.


                 (1)  Hickey et al. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing (2013)         

Version of Test: 8

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