Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.2.1.22 (cystathionine beta-synthase)
965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutations in the human cystathionine beta-synthase (CBS) gene are known to cause homocystinuria and may also be a significant risk factor for premature atherosclerosis. We have previously shown that the human CBS protein can substitute for the endogenous yeast CBS protein in Saccharomyces cerevisiae. We now show that expression of three different CBS mutants known to be associated with reduced enzyme activity in humans fail to complement growth in the yeast assay. In addition, we have used the yeast CBS assay to identify eight mutant CBS alleles in cell lines from patients with CBS deficiency. These mutant alleles include two previously identified and five novel CBS mutations. Our results also demonstrate that the yeast CBS assay can detect a large percentage of individuals heterozygous for mutations in CBS. This system should be useful in determining the relationship between CBS mutations and human disease.
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PMID:A yeast assay for functional detection of mutations in the human cystathionine beta-synthase gene. 852 2

Two separate metabolic pathways that methylate homocysteine to methionine are known in humans, utilizing, respectively, 5-methyltetrahydrofolate and betaine as methyl donors. Deficiency of the folate-dependent methylation system is linked to hyperhomocysteinemia. Our data suggest that this deficiency leads to concurrent metabolic down-regulation of homocysteine transsulfuration that may contribute to hyperhomocysteinemia. By contrast, no instances have been reported of hyperhomocysteinemia resulting from deficiencies of betaine-dependent homocysteine methylation. Long-term betaine supplementation of 10 patients, who had pyridoxine-resistant homocystinuria and gross hyperhomocysteinemia due to deficiency of cystathionine beta-synthase activity, caused a substantial lowering of plasma homocysteine, which has now been maintained for periods of up to 13 years. Betaine had to be taken regularly because the effect soon disappeared when treatment was stopped. In conclusion, depressed activity of the transsulfuration pathway may contribute to hyperhomocysteinemia because of primary deficiencies of enzymes of either the transsulfuration or of the folate-dependent methylation pathways. Stimulation of betaine-dependent homocysteine remethylation causes a commensurate decrease in plasma homocysteine that can be maintained as long as betaine is taken.
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PMID:Human homocysteine catabolism: three major pathways and their relevance to development of arterial occlusive disease. 864 74

We compared biochemical and molecular methods for the identification of heterozygous carriers of mutations in the cystathionine beta-synthase (CBS) gene. Eleven relatives of seven unrelated patients with homocystinuria due to homozygous CBS deficiency and controls were studied with respect to total homocysteine concentrations before and after methionine loading. In addition, we determined CBS activity in cultured skin fibroblasts and tested for the presence of five known mutations by a PCR-based method in these seven patients, their relatives and controls. The results demonstrate that measurement of homocysteine after methionine loading and assay of CBS enzyme activity in cultured fibroblasts identify most but not all heterozygotes. There was significant correlation between homocysteine concentrations and CBS activities only after methionine loading (r = 0.12, 0.48, 0.48 and 0.50 at 0, 4, 6 and 8 h, respectively). Among the homozygous patients, molecular approaches identified five T833C and two G919A mutations out of 14 independent alleles, confirming the studies of others that these represent the two most prevalent mutations. In addition, we found that three of six heterozygotes with the T833 C allele had post-methionine loading homocysteine levels which overlapped with controls and of the other three, one (as well as an obligate heterozygote who did not carry any of the five mutant alleles tested) had CBS activity comparable to that of controls. These findings demonstrate that genotyping is useful as an adjunctive method for the diagnosis of the heterozygous carrier state of CBS deficiency.
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PMID:Molecular and biochemical approaches in the identification of heterozygotes for homocystinuria. 872 13

We determined the molecular basis of cystathionine beta-synthase (CBS) deficiency in a partially pyridoxine-responsive homocystinuria patient. Direct sequencing of the entire CBS cDNA revealed the presence of a homozygous G1330A transition. This mutation causes an amino acid change from aspartic acid to asparagine (D444N) in the regulatory domain of the protein and abolishes a TaqI restriction site at DNA level. Despite the homozygous mutation, CBS activities in extracts of cultured fibroblasts of this patient were not in the homozygous but in the heterozygous range. Furthermore, we observed no stimulation of CBS activity by S-adenosylmethionine, contrary to a threefold stimulation in control fibroblast extract. The mutation was introduced in an E. coli expression system and CBS activities were measured after addition of different S-adenosylmethionine concentrations (0-200 microM). Again, we observed a defective stimulation of CBS activity by S-adenosylmethionine in the mutated construct, whereas the normal construct showed a threefold stimulation in activity. These data suggest that this D444N mutation interferes in S-adenosylmethionine regulation of CBS. Furthermore, it indicates the importance of S-adenosylmethionine regulation of the transsulfuration pathway in homocysteine homeostasis in humans.
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PMID:Defective cystathionine beta-synthase regulation by S-adenosylmethionine in a partially pyridoxine responsive homocystinuria patient. 875 36

Homocystinuria, due to a deficiency of the enzyme cystathionine beta-synthase (CBS), is an inborn error of sulphur-amino acid metabolism. This is an autosomal recessive disease which results in hyperhomocysteinaemia and a wide range of clinical features, including optic lens dislocation, mental retardation, skeletal abnormalities and premature thrombotic events. We report the identification of 5 missense mutations in the protein-coding region of the CBS gene from 3 patients with pyridoxine-nonresponsive homocystinuria. Reverse-transcription PCR was used to amplify CBS cDNA from each patient and the coding region was analysed by direct sequencing. The mutations detected included 3 novel (1058C-->T, 992C-->A and 1316G-->A) and 2 previously identified (430G-->A and 833C-->T) base alterations in the CBS cDNA. Each of these mutations predicts a single amino acid substitution in the CBS polypeptide. Appropriate cassettes of patient CBS cDNA, containing each of the above defined mutations, were used to replace the corresponding cassettes of normal CBS cDNA sequence within the bacterial expression vector pT7-7. These recombinant mutant and normal CBS constructs were expressed in Escherichia coli cells and the catalytic activities of the mutant proteins were compared with normal. All of the mutant proteins exhibited decreased catalytic activity in vitro, which confirmed the association between the individual mutation and CBS dysfunction in each patient.
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PMID:Characterisation of five missense mutations in the cystathionine beta-synthase gene from three patients with B6-nonresponsive homocystinuria. 915 16

Among 40 patients with homocystinuria due to cystathionine beta-synthase deficiency diagnosed in the state of New South Wales, Australia (population 6 million) and followed long-term, there were 10 deaths at ages 2-30 years. Of these 8 were definite vascular deaths, one was a presumed vascular death, and the other was due to an accident and unrelated to homocystinuria. The vascular deaths were all early cases and only one patient, a pyridoxine-responsive 30-year-old woman, had been prescribed adequate treatment although it was uncertain that she was taking it. In 32 patients of mean age 30 years (range 9-66 years) there were 539 patient-years of treatment with pyridoxine, folic acid and hydroxocobalamin. There were 17 pyridoxine-responsive patients and all maintained plasma total free homocyst(e)ine levels < 20 mumol/L over an average treatment period of 16.6 years. The 15 nonresponsive patients received additionally 6-9 g of betaine daily. This resulted in a further 74% mean decline (+/-14% SD) in plasma total free homocyst(e)ine, persisting during an average (post-betaine) treatment period of 11 years; current mean +/- SD levels are 33 +/- 17 mumol/L (n = 15). There were two vascular events during treatment, one fatal pulmonary embolus (see above) and one myocardial infarction, whereas without treatment, 21 would have been expected, chi2 = 14.22, p = 0.0001, relative risk 0.09 (95% CI 0.02-0.38). There were no events during 258 patient-years of treatment in the 15 pyridoxine-nonresponsive patients (p < 0.005 versus expected untreated). Nineteen patients had a total of 19 major and 15 minor operations requiring anaesthetic, and three had successful pregnancies, one whilst receiving betaine. There were no thromboembolic complications. We conclude that treatment which effectively lowers circulating homocyst(e)ine, even to suboptimal levels, markedly reduces cardiovascular risk in patients with cystathionine beta-synthase deficiency, and that betaine therapy contributes importantly to this in pyridoxine-nonresponsive patients. Betaine as additional therapy is safe and effective for at least 16 years.
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PMID:The natural history of vascular disease in homocystinuria and the effects of treatment. 921 Dec 1

We used single-strand conformational polymorphism and direct nucleotide sequencing to identify a novel mutation in the cystathionine beta-synthase (CBS) gene of two siblings with homocystinuria. Both patients are heterozygous carriers of the G919A transition and the novel mutation which involves a G-to-A transition in the intron 12 splice donor site. Reverse transcription of RNA harvested from transformed lymphocytes followed by PCR showed a normal size product along with two shorter products involving the deletion of either exon 12 alone or both exons 11 and 12. To our knowledge, the skipping of more than one exon through a single base substitution at a splice-donor site has not been previously reported. The normal size splice product was found to have either a G or an A at nucleotide position 919, indicating that normal size mRNA was produced by both alleles.
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PMID:Identification of a splice site mutation in the cystathionine beta-synthase gene resulting in variable and novel splicing defects of pre-mRNA. 923 91

Homocystinuria due to cystathionine beta-synthase (CS) deficiency is the most common inborn error of methionine metabolism. Patients with CS-deficiency have an extremely high risk of vascular disease. The underlying mechanism is still unsolved. Dysfunction of endothelial cells could be the trigger in the formation of atherosclerosis and thrombosis. Therefore, differences in cell function were studied between normal and CS-deficient human umbilical endothelial cells (HUVECs). Total homocysteine (tHcy) concentrations in culture media as a measure of homocysteine export increased in all cell lines, including the cell line with CS-deficiency, with constant amounts of approximately 2.5 microM every 24 h. von Willebrand factor (vWF), tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) in culture media were used as markers of endothelial function and increased also with progression of culture time. The effects of additions of folate, vitamin B6 and methionine to the culture medium were studied. The homocysteine export and the markers of endothelial function did not differ between the control and the CS-deficient HUVECs under various test conditions. These data show that CS-deficient endothelial cells have normal homocysteine export and normal endothelial cell function. In CS-deficient patients the very high blood levels of homocysteine, probably due to deficient CS function in liver and kidney, seems to be the hazardous factor to endothelial cells, thus promoting atherosclerosis and thrombosis in CS-deficient patients.
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PMID:Homocysteine metabolism in endothelial cells of a patient homozygous for cystathionine beta-synthase (CS) deficiency. 926 79

Homocystinuria is a rare autosomal recessive disease characterized by homocystinuria and multisystemic clinical disorders. The term denotes a biochemical abnormality of methionine metabolism caused both by transsulfuration pathway disorders and remethylation of homocysteine into methionine, and as such it can be a result of numerous specific and different genetic lesions. Homocystinuria is most commonly caused by deficiency of cystathionine beta-synthase (CBS) activity (EC 4.2.1.22). In this lesion, depending on specific characteristics of mutant enzyme molecules, in regard to existence of residual activity, responsive and nonresponsive homocystinuria can be differed regarding clinical response to high doses of pyridoxine. Although there are numerous different clinical abnormalities, changes on four organ systems are dominant. The most common symptoms of homocystinuria include lens dislocation, vascular disorders, skeletal abnormalities and mental retardation. Laboratory findings are the first diagnostic procedure, while determination of enzymatic activity is a direct parameter for making diagnosis. Prenatal diagnosis and early detection are extremely important for the course and prognosis of the disease as they enable application of currently available therapy as soon as possible. The presently available therapy can, only in such cases, prevent occurrence of serious clinical symptoms, prevent their advancement to some extent or improve reversible clinical manifestations.
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PMID:[Homocystinuria--biochemical, clinical and genetic aspects]. 929 49

We present two siblings with vitamin B6-nonresponsive homocystinuria due to a deficiency of cystathionine beta-synthase who had different levels of methionine in the blood during the neonatal period, even though they had the same genetic defect. One of them was missed in the screening of newborns for homocystinuria. Special care should be taken in screening neonates for homocystinuria using the blood level of methionine.
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PMID:Two siblings with vitamin B6-nonresponsive cystathionine beta-synthase deficiency and differing blood methionine levels during the neonatal period. 939 25


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