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Coagulation

Hereditary thrombophilia / hypercoagulopathies

Hyperhomocysteinemia


Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 21 June 2012, last major update June 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

General
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● Homocysteine is an amino acid, derived from methionine, may be converted to cysteine
● Its metabolic pathways require vitamins B12, B6 and folate
● Elevated levels may be hereditary (due to mutations in these pathways) or acquired (due to deficiencies of vitamins B12, B6 or folate, renal failure, carcinoma, hypothyroidism or medications)
● Elevations in homocysteine are associated with increased risk of arterial and venous thrombosis and atherosclerosis, based on retrospective case control studies
● Prospective studies show a weak positive association with arterial thrombosis, and no definite association for venous thrombosis
● Homozygosity or heterozygosity for the C677T mutation in MTHFR gene (methylene tetrahydrofolate reductase), which is involved in homocysteine metabolic pathway, does not appear to be a risk factor for thrombosis, but may be significant in folate-deficient patients
● Although MTHFR was previously thought to be associated with thrombosis, newer data suggests this test is not useful in the first-line evaluation of thrombosis
● Mutation in the methioninesynthetase gene (MTR) also can lead to increased homocystein levels but, as with MTHFR mutations, are not thought to be associated with thrombosis
● Consider testing patients with documented coronary artery disease, cerebrovascular disease or peripheral vascular disease for homocysteine
● High levels can be treated with vitamins B6, B12, folic acid, trimethylglycine, although they may not reduce the risk of future cardiovascular events
● Homocysteinemia is usually associated with a moderately elevated plasma homocysteine, while homocysteinuria is a specific genetic entity with very high plasma homocysteine levels

Diagrams
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Folate metabolism

Additional references
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Arch Pathol Lab Med 2002;126:1367, Hematol J 2001;2:38

End of Coagulation > Hereditary thrombophilia / hypercoagulopathies > Hyperhomocysteinemia


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