Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Elevated levels of plasma homocysteine are associated with both venous and arterial thrombosis. Homocysteine inhibits the function of thrombomodulin, an anticoagulant glycoprotein on the endothelial surface that serves as a cofactor for the activation of protein C by thrombin. The effects of homocysteine on thrombomodulin expression and protein C activation were investigated in cultured human umbilical vein endothelial cells and CV-1(18A) cells that express recombinant human thrombomodulin. Addition of 5 mM homocysteine to endothelial cells produced slight increases in thrombomodulin mRNA and thrombomodulin synthesis without affecting cell viability. In both cell types, thrombomodulin synthesized in the presence of homocysteine remained sensitive to digestion with endoglycosidase H and failed to appear on the cell surface, suggesting impaired transit along the secretory pathway. In a cell-free protein C activation assay, homocysteine irreversibly inactivated both thrombomodulin and protein C in a process that required free thiol groups and was inhibited by the oxidizing agents diamide or N-ethylmaleimide. By inhibiting both thrombomodulin surface expression and protein C activation, homocysteine may contribute to the development of thrombosis in patients with cystathionine beta-synthase deficiency.
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PMID:Inhibition of thrombomodulin surface expression and protein C activation by the thrombogenic agent homocysteine. 166 Dec 91

The link between vascular disease and elevated homocysteine levels has been recognized for more than 30 years, and association with moderately elevated levels has been suspected for 20 years. Homocysteine is a sulfhydryl-containing amino acid that is formed by the demethylation of methionine. It is normally catalysed to cystathionine by cystathionine beta-synthase a pyridoxal phosphate-dependent enzyme. Homocysteine is also remethylated to methionine by methionine synthase, a vitamin B12 dependent enzyme and by methylenetetrahydrofolate reductase. Environmental factors such as folate, or vitamin B12, or vitamin B6 deficiencies and genetic defects such as cystathionine beta-synthase or abnormality of methylene-tetrahydrofolate reductase or some vitamin B12 metabolism defects may contribute to increasing plasma homocysteine levels. Normal fasting levels of homocysteine lie within the range 6-16 mumol/l. Apart from differences in assay methods, age, sex and nutritional status may affect the plasma levels. Though it is now well known that homocysteine is an independent risk factor for premature vascular disease, the pathogenesis of homocysteine-induced vascular damage is, for the most part, unknown. It may be multifactorial, including direct homocysteine damage to the endothelium, an enhanced low-density lipoprotein peroxidation, an increase of platelet thromboxane A2, or a decrease of protein C activation.
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PMID:[Deregulation of homocysteine metabolism and consequences for the vascular system]. 923 30

Thromboembolic disease results from an hypercoagulable state and multifactorial causes may lead to hypercoagulability. Thrombogenic risk factors can be acquired and/or inherited. For each thrombophilic patient, the main clinical features retained are: the patient age, the familial history, the recurrence of thromboembolic events, an unusual site of thrombosis. Anti-phospholipid antibodies, which are considered as acquired thrombogenic risk factors, can be detected with coagulation tests and/or Elisa methods. The association of antiphospholipid antibodies with thrombosis is defined as the anti-phospholipid syndrome. Last decades, genetic risk factors were identified. First of all, antithrombin, protein C and protein S deficiencies were described. These deficiencies are involved in about 10% of patients who develop thrombosis before the age of 50. In 1993, a new genetic risk factor was discovered: activated protein C resistance which is due to the Q506 mutation in factor V. This defect represents the most prevalent abnormality of inherited thrombophilia, affecting 20 to 40% of thrombophilic patients. Interestingly, hyperhomocysteinemia, known as potentially predisposing to arterial disease, was also recognized as a risk factor for venous occlusive disease. Several genes encoding homocystein metabolism enzymes, such as cystathionine beta-synthase or methylenetetrahydrofolate reductase are concerned. Establishment of a causal association between the presence of a biological abnormality and the occurrence of thrombosis may lead to an adapted prophylaxis whatever the risk situation.
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PMID:[Evaluation of hemostasis in venous thromboembolism pathology]. 975 22

Thrombosis is the major cause of morbidity and mortality in individuals with untreated classical homocystinuria (HCU) due to cystathionine beta-synthase deficiency and characterised by severe hyperhomocysteinaemia. In addition, mild and moderate hyperhomocysteinaemia and Factor V Leiden (FVL; Arg506Gln) have recently been identified as thrombotic risk factors. FVL. which renders resistance to activated Protein C, is the most common inherited genetic risk factor for thrombosis with a high allelic frequency amongst Caucasians. As thrombophilia is a multigenic disorder, 26 individuals with HCU (median age 17.6 years, range 3.5-32.8 years) and 36 obligate heterozygotes (median age 51.5 years, range 34-74 years) were screened for FVL. All the HCU individuals received treatment, except one, within 6 weeks of birth for those who were diagnosed at birth through the national newborn screening programme (n = 20) and at the time of diagnosis for those late detected (n = 5, mean age of starting treatment 4.9 years, range 1.4-11 years). All had been free from venous thrombosis, except one HCU individual and one HCU obligate heterozygote. Neither of the two individuals with venous thrombosis carried FVL. Two independent individuals with HCU (male 14.8 years; female 18.2 years) were heterozygous for FVL (allelic frequency 3.8%) and three independent HCU obligate heterozygotes (males 40 and 45.8 years; female 45.6 years) were also heterozygous for FVL (allelic frequency 4.16%). The findings in this small group suggest that FVL is not a mandatory but a significant confounding risk factor for the occurrence of thrombosis in HCU individuals and additional contributing factors may be required for thrombosis to occur in HCU obligate heterozygotes with FVL heterozygosity. Our data also suggest that treatment of HCU not only reduces the thrombotic risk in patients with isolated HCU but also in those with the additional FVL heterozygosity.
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PMID:Factor V Leiden (Arg506Gln), a confounding genetic risk factor but not mandatory for the occurrence of venous thromboembolism in homozygotes and obligate heterozygotes for cystathionine beta-synthase deficiency. 1023 28

The frequency of the heterozygous 844ins68 mutation of the cystathionine beta-synthase (CBS) gene and of its association with the homozygous C677T transition of the methylenetetrahydrofolate reductase (MTHFR) gene, plasma fasting tHcy, folate and vitamin B12 levels were evaluated in 309 consecutive patients with objectively diagnosed early-onset venous (n = 200) or arterial thromboembolic disease (n = 109) recruited over 25 months in Milan (North Italy) and Naples (South Italy). The above gene polymorphisms were also evaluated in a population of 787 unmatched controls, 204 of whom--similar to patients for age- and sex-distribution--had fasting tHcy, vitamins and activated protein C resistance measured in their plasma. Moderate fasting hyperhomocysteinemia was detected in 15.5% of patients and in 5.9% of 204 controls (Mantel-Haenszel OR after stratification for type of occlusive disease and gender: 2.88; 1.48-5.32). The frequencies of the 677TT mutation of the MTHFR gene and of the heterozygous 844ins68 insertion of the CBS gene were not significantly different in the patient (19.4% and 6.9%) and the control population (16.5% and 7.8%), but the association of the two gene polymorphisms found in 3.9% of patients and in 1.1% of controls - was significantly associated with an increased risk of venous or arterial occlusive diseases (RR = 3.63; 1.48-8.91). The MTHFR 677TT mutation (RR: 6.92; 3.86-12.4) and its association with the 844ins68 insertion (RR: 21.9; 8.35-57.4), but not the isolated insertion (RR: 0.71), were more frequent in patients and controls with fasting hyperhomocysteinemia than in normohomocysteinemic subjects, irrespective of the type of occlusive disease (venous or arterial). When adjusted for determinants of hyperhomocysteinemia in the patient and the control populations (generalized linear model), fasting tHcy levels were significantly higher in subjects with association of the two gene abnormalities (24.2+/-3.8 micromol/L) than in subjects with the MTHFR 677TT mutation only (14.0+/-5.8 micromol/L, p = 0.004). Activated protein C resistance was significantly more prevalent in venous patients (9.9%) than in controls (3.9%, OR = 2.69; 1.08-6.88). Six of 21 venous patients with APC-resistance also had hyperhomocysteinemia (RR = 5.04; 0.68-37.6), but isolated fasting hyperhomocysteinemia retained statistical significance for the association with venous occlusive disease (RR = 2.84; 1.34-6.01). Heterozygosity for the 844ins68 mutation of the CBS gene is not per se a risk factor for premature arterial and/or venous occlusive diseases. However, when detected in combination with thermolabile MTHFR, it increases by almost 4-fold the risk of occlusive diseases (arterial and/or venous), by increasing the risk and the degree of fasting hyperhomocysteinemia.
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PMID:Contribution of the cystathionine beta-synthase gene (844ins68) polymorphism to the risk of early-onset venous and arterial occlusive disease and of fasting hyperhomocysteinemia. 1105 53

Venous and arterial thromboembolism can occur in patients with homocystinuria. Resistance to activated protein C, which is caused by a single point mutation in the gene for factor V, renders an individual at risk for thrombosis. It has been suggested that coexistence of hereditary homocystinuria and factor V Leiden mutation might jointly play a role in the development of thrombosis. We analysed six patients with homocystinuria due to cystathionine beta-synthase deficiency for factor V Leiden and prothrombin G20210A mutations. Only one patient was found to have the factor V Leiden mutation in homozygous form and this patient had suffered from severe thrombosis. One patient was found to be heterozygous with no documented thrombosis. None of the patients had prothrombin G20210A mutation. We stress the necessity for screening for known thrombophilic risk factors in patients with cystathonine beta-synthase deficiency. The coexistence of the factor V Leiden mutation can cause severe thrombotic events in patients with homocystinuria.
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PMID:Factor V Leiden mutation in Turkish patients with homozygous cystathionine beta-synthase deficiency. 1148 2

Aberrant DNA methylation is recognized as being a common feature of human neoplasia.CpG island hypermethylation and global genomic hypomethylation occur simultaneously in the cancer cell. However, very little is known about the interindividual inherited susceptibility to these epigenetic processes. To address this matter, we have genotyped in 233 cancer patients (with colorectal, breast, or lung tumors), four germ-line variants in three key genes involved in the metabolism of the methyl group, methylene-tetrahydrofolate reductase, methionine synthase, and cystathionine beta-synthase, and analyzed their association with DNA methylation parameters. The epigenetic features analyzed were the 5-methylcytosine content in the genome of the tumors and their normal counterparts, and the presence of CpG island hypermethylation of tumor suppressor genes (p16(INK4a), p14(ARF), hMLH1, MGMT, APC, LKB1, DAPK, GSTP1, BRCA1, RAR beta 2, CDH1, and RASSF1). Two positive associations were found. First, carriers of genotypes containing the methylene-tetrahydrofolate reductase 677T allele show constitutive low levels of 5-methylcytosine in their genomes (P = 0.002), and tumors in these patients do not achieve severe degrees of global hypomethylation (P = 0.047). Second, tumors occurring in homozygous carriers of the methionine synthase 2756G allele show a lower number of hypermethylated CpG islands of tumor suppressor genes (P = 0.029). The existence of these associations may provide another example of the interplay between genetic and epigenetic factors in the cancer cell.
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PMID:Germ-line variants in methyl-group metabolism genes and susceptibility to DNA methylation in normal tissues and human primary tumors. 1215 64

Hyperhomocysteinemia has been proposed to inhibit the protein C anticoagulant system through 2 mechanisms: decreased generation of activated protein C (APC) by thrombin, and resistance to APC caused by decreased inactivation of factor Va (FVa). We tested the hypotheses that generation of APC by thrombin is impaired in hyperhomocysteinemia in monkeys and that hyperhomocysteinemia produces resistance to APC in monkeys, mice, and humans. In a randomized crossover study, cynomolgus monkeys were fed either a control diet or a hyperhomocysteinemic diet for 4 weeks. Plasma total homocysteine (tHcy) was approximately 2-fold higher when monkeys were on the hyperhomocysteinemic diet than when they were on the control diet (9.8 +/- 2.0 microM versus 5.6 +/- 1.0 microM; P <.05). After infusion of human thrombin (25 microg/kg of body weight), the peak level of plasma APC was 136 +/- 16 U/mL in monkeys fed the control diet and 127 +/- 13 U/mL in monkeys fed the hyperhomocysteinemic diet (P >.05). The activated partial thromboplastin time was prolonged to a similar extent by infusion of thrombin in monkeys fed the control diet and in those fed the hyperhomocysteinemic diet. The sensitivity of plasma FV to human APC was identical in monkeys on control diet and those on hyperhomocysteinemic diet. We also did not detect resistance of plasma FV to APC in hyperhomocysteinemic mice deficient in cystathionine beta-synthase (plasma tHcy, 93 +/- 16 microM) or in human volunteers with acute hyperhomocysteinemia (plasma tHcy, 45 +/- 6 microM). Our findings indicate that activation of protein C by thrombin and inactivation of plasma FVa by APC are not impaired during moderate hyperhomocysteinemia in vivo.
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PMID:Effect of hyperhomocysteinemia on protein C activation and activity. 1260 65

The role of methylenetetrahydrofolate reductase (MTHFR) TT677 genotype, cystathionine beta-synthase (CBS) 844ins68 mutation and endothelial cell protein C receptor (EPCR) 4031ins23 in the development of deep-vein thrombosis (DVT) was investigated in 300 consecutive DVT patients and 410 healthy blood donors. MTHFR TT677 was found in 40 (13.3%) patients and in 59 (14.4%) controls (OR 0.92; 95% C.I. 0.54-1.41); CBS 844ins68 in 20 (6.7%) patients and in 56 (13.7%) control subjects (OR 0.45; 95% C.I. 0.27-0.77); and the combination of MTHFR TT677 with CBS 844ins68 in 4 (1.3%) patients and in 7 (1.7%) controls (OR 0.78; 95% C.I. 0.23-2.68). Logistic regression analysis did not show a further increase of risk for MTHFR TT677 or CBS 844ins68 in combination with the factor V Leiden or the prothrombin gene G20210A mutations. The EPCR 4031ins23 was observed in 2 patients (0.66%) and none of the controls. In conclusion, MTHFR TT677 does not appear to be an important risk factor for DVT, EPCR 403ins23 seems to be very rare, its role in the development of DVT unclear. A putative protective effect of CBS 844ins68 should be further investigated.
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PMID:CBS 844ins68, MTHFR TT677 and EPCR 4031ins23 genotypes in patients with deep-vein thrombosis. 1241 83

Mutations such as factor V Leiden G1691A (FVL), prothrombin G20210A (FIIM), methylenetetrahydrofolate reductase (MTHFR) C677T, cystathionine beta-synthase (CBS) 844ins68 and endothelial cell protein C receptor (EPCR) 4031ins23 are risk factors for thromboembolism. To assess the role of these mutations in young adults with cerebral ischemia of otherwise undetermined etiology, 93 patients younger than 50 years old with thromboembolic strokes or transient ischemic attacks were studied. One hundred and eighty-six healthy age-matched and sex-matched blood donors served as controls. The FVL mutation was detected in 15/93 patients and 13/186 controls. After adjustment for smoking, arterial hypertension, and hyperlipidemia, the association of the FVL mutation with cerebral ischemia [odds ratio (OR), 3.19; 95% confidence interval (CI), 1.38-7.39] remained significant. One of 93 patients and 6/186 controls were carriers of FIIM (OR, 0.33; 95% CI, 0.04-2.75). We detected the MTHFR TT677 genotype in 9/93 patients and 26/186 controls (OR, 0.66; 95% CI, 0.30-1.47), a CBS 844ins68 mutation in 12/93 patients and 19/186 controls (OR, 1.30; 95% CI, 0.60-2.81), and an EPCR 4031ins23 mutation in 1/93 patients and in no control individual (P = 0.33). In conclusion, in younger adults the FVL mutation is a risk factor for cerebrovascular disease. FIIM, the MTHFR TT677 genotype and the CBS 844ins68 mutation did not contribute to the risk in this group of patients. The EPCR 4031ins23 mutation is very rare, its possible role needs further investigation.
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PMID:Genetic risk factors in young adults with 'cryptogenic' ischemic cerebrovascular disease. 1243 43


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