Hyperhomocysteinemia: Description, Causes and Risk Factors:
Hyperhomocysteinemia is a naturally occurring amino acid that, if present at a high level in the blood, can produce an increased risk of blood clots. This condition is known as hyperhomocysteinemia. People with hyperhomocysteinemia may get blood clots in either the veins (e.g. deep vein thrombosis and pulmonary embolism) or arteries (e.g. stroke and heart attack). It is believed that high blood levels of homocysteine can damage the lining of blood vessels. This damage is what can lead to blood clots. In addition to making people prone to blood clots, hyperhomocysteinemia will also increase the risk of birth defects, dementia (e.g., Alzheimer's disease), and bone fractures. Common causes of hyperhomocysteinemia include kidney disease, lack of B vitamins (such as folate, vitamin B12, and vitamin B6) in the diet, hypothyroidism, alcoholism, and certain medications.
Patients with kidney failure who are undergoing dialysis also have an increased risk of developing hyperhomocysteinemia. However, researchers have not discovered exactly why this condition may develop in dialysis patients.
Other conditions that may increase an individual's risk of developing hyperhomocysteinemia include hypothyroidism, liver disease, metabolic disorders (especially those leading to nutritional deficiencies), genetic abnormalities, and certain types of cancer. Some medications may also elevate homocysteine levels in the blood.
A condition known as homocystinuria (cystathionine beta-synthase deficiency) may cause elevated levels of homocysteine in the blood. This is a rare genetic (inherited) disorder that affects the enzyme cystathionine beta-synthase. This enzyme is involved in the metabolism of homocysteine. In homocystinuria, cystathionine beta-synthase does not work properly. As a result, homocysteine accumulates in the blood.
Inheritable differences in the methylenetetrahydrofolate reductase (MTHFR) gene may also lead to increased levels of homocysteine in the blood. This gene contains the instructions for making the MTHFR enzyme, which is involved in the conversion of homocysteine to methionine. Genetic differences in the MTHFR gene are quite common, and certain variations that cause the gene to be defective have been linked to increased risk of cardiovascular disease.
The association of hyperhomocysteinemia and arterial and venous thrombosis is controversial. Severe hyperhomocysteinemia is associated with atherosclerosis. The effect of mild hyperhomocysteinemia is less certain. Coinheritance of methylenetetrahydrofolate reductase defects and factor V Leiden is likely to increase the risk of venous thromboembolism. The association of methylenetetrahydrofolate reductase defects combined with no additional thrombophilic risk factors with venous thrombosis is less clear. High doses of folic acid to lower homocysteine levels might not be necessary.
Hyperhomocysteinemia usually does not cause any obvious symptoms. Therefore, the American Heart Association (AHA) recommends regular homocysteine
testing in patients who have a high risk of developing heart disease
The diagnosis of hyperhomocysteinemia is made by measuring the level of total homocysteine in the blood.Some people inherit defects that cause hyperhomocysteinemia. Most people with inherited defects are only mildly affected. In rare cases, however, inherited defects in genes produce a severe form of hyperhomocysteinemia called homocystinuria. People affected with homocystinuria have a very high risk of blood clots, and also may suffer from mental retardation, bone abnormalities, and visual problems.
The primary goal of treatment is to lower blood levels of homocysteine to normal. Treatment may consist of giving supplements of folic acid, vitamin B12
, and/or vitamin B6
. It also may include anticoagulant medications (blood thinners), such as aspirin, clopidogrel, heparin, low-molecular weight heparin, or warfarin, to prevent blood clots. Patients with the severe form of hyperhomocysteinemia (homocystinuria) are often treated with high doses of vitamin B6
or betaine, and the amount of methionine consumed in the diet may be restricted.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.