Homozygosity for the c.665C>T variant in the Methylene tetrahydrofolate reductase (MTHFR) gene may be associated with increased levels of homocysteine. Note, the c.665C>T variant is also known as the thermolabile variant, and historically as C677T.
Individuals who are homozygous for c.665C>T, but have a normal homocysteine leveI are not at increased risk for venous thromboembolism or recurrent pregnancy loss. Individuals who are homozygous for the c.665C>T variant and have an elevated homocysteine level have a mildly increased risk for either event. There is no evidence of an association with mortality caused by cardiovascular disease. Women who are homozygous for the c.665C>T variant have a moderately increased risk to have a baby with a neural tube defect.
Please note, current knowledge indicates that the presence of a single copy of the c.665C>T variant is not associated with significant health risks. Therefore, heterozygosity for the c.665C>T variant is not reported by this laboratory. In addition, this assay does not assess the c.1286A>C variant in the MTHFR gene because it is reported to have limited clinical significance.