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Causes of high and low homocysteine
Last reviewed: 06.07.2025
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High homocysteine concentrations are the most important factor in the early development of atherosclerosis and thrombosis. Hyperhomocysteinemia is detected in 13-47% of patients with coronary heart disease. Currently, the determination of the concentration of homocysteine in the blood serum is used as a marker of the development of coronary heart disease. High concentration of homocysteine in the blood of patients with coronary heart disease is a clear harbinger of acute episodes that can lead to death. According to the degree of severity, hyperhomocysteinemia is divided into mild (15-25 μmol / l), moderate (25-50 μmol / l) and severe (50-500 μmol / l). In patients with coronary heart disease with a homocysteine concentration in the blood below 10 μmol / l, stenosis of the coronary arteries is usually less than 50%, at a level of 10-15 μmol / l - 80%, above 15 μmol / l - 90%.
Congenital homocystinuria is a monogenic metabolic defect caused by a deficiency of methylenetetrahydrofolate reductase. Patients have significantly increased plasma homocysteine concentrations (50-500 μmol/l) and its excretion in urine.
In heterozygotes for the cystathionine-β-synthetase defect, the concentration of homocysteine in the blood is within the normal range, therefore, a methionine loading test is used to detect the disease. This test is carried out in 2 stages. Initially, a control study is carried out. A blood sample is taken immediately after breakfast and after 2, 4, 6 and 8 hours. Normally, a transient peak of an increase in the concentration of homocysteine occurs between 4 and 8 hours. On the second day, blood for research is taken immediately before the load and after 2, 4, 6 and 8 hours after oral administration of methionine (100 mg/kg). The test is considered positive if the concentration of homocysteine in the blood during this period of time exceeds the results of the control test by an amount equal to or greater than 2 standard deviations.
Currently, the mechanisms that determine the role of increased homocysteine concentration in the blood in the pathogenesis of atherosclerosis are actively discussed. A negative correlation has been established between the concentrations of homocysteine and folates in the blood, as well as vitamins B 6 and B 12. Deficiency of these substances in the body is accompanied by an increase in the concentration of homocysteine in the blood. The use of folates, vitamins B6 and B 12 (cofactors of methionine metabolism enzymes) in the treatment of patients with hyperhomocysteinemia has shown their effectiveness. With effective therapy, the concentration of homocysteine in the blood serum should not exceed 10 μmol / l.
Hyperhomocysteinemia may also be one of the manifestations of a neoplastic process, in particular, in breast, ovarian and pancreatic cancer, ALL. An increase in the concentration of homocysteine in the blood serum is possible with hypothyroidism, severe psoriasis, long-term use of theophylline preparations, estrogen-containing contraceptives, cytostatics (methotrexate) and antiepileptic drugs (phenytoin, carbamazepine), due to impaired metabolism and absorption of vitamin B 12 and folic acid.