Cystathionine beta-synthase (CBS) deficiency is a rare inherited disorder in the methionine catabolic pathway, in which the impaired synthesis of cystathionine leads to accumulation of homocysteine. Patients can present to many different specialists and diagnosis is often delayed. Severely affected patients usually present in childhood with ectopia lentis, learning difficulties and skeletal abnormalities. These patients generally require treatment with a low-methionine diet and/or betaine. In contrast, mildly affected patients are likely to present as adults with thromboembolism and to respond to treatment with pyridoxine. In this article, we present recommendations for the diagnosis and management of CBS deficiency, based on a systematic review of the literature. Unfortunately, the quality of the evidence is poor, as it often is for rare diseases. We strongly recommend measuring the plasma total homocysteine concentrations in any patient whose clinical features suggest the diagnosis. Our recommendations may help to standardise testing for pyridoxine responsiveness. Current evidence suggests that patients are unlikely to develop complications if the plasma total homocysteine concentration is maintained below 120 μmol/L. Nevertheless, we recommend keeping the concentration below 100 μmol/L because levels fluctuate and the complications associated with high levels are so serious.

• MeSH
• betain metabolismus   MeSH
• cystathionin-beta-synthasa nedostatek   MeSH
• homocystein metabolismus   MeSH
• homocystinurie dietoterapie   farmakoterapie   MeSH
• lidé MeSH
• methionin metabolismus   MeSH
• pyridoxin terapeutické užití   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• systematický přehled MeSH
• Názvy látek
• betain MeSH
• cystathionin-beta-synthasa MeSH
• homocystein MeSH
• methionin MeSH
• pyridoxin MeSH

Misfolding of mutant enzymes may play an important role in the pathogenesis of cystathionine beta-synthase (CBS) deficiency. We examined properties of a series of 27 mutant variants, which together represent 70% of known alleles observed in patients with homocystinuria due to CBS deficiency. The median amount of SDS-soluble mutant CBS polypeptides in the pellet after centrifugation of bacterial extracts was increased by 50% compared to the wild type. Moreover, mutants formed on average only 12% of tetramers and their median activity reached only 3% of the wild-type enzyme. In contrast to the wild-type CBS about half of mutants were not activated by S-adenosylmethionine. Expression at 18 degrees C substantially increased the activity of five mutants in parallel with increasing the amounts of tetramers. We further analyzed the role of solvent accessibility of mutants as a determinant of their folding and activity. Buried mutations formed on average less tetramers and exhibited 23 times lower activity than the solvent exposed mutations. In summary, our results show that topology of mutations predicts in part the behavior of mutant CBS, and that misfolding may be an important and frequent pathogenic mechanism in CBS deficiency.

• MeSH
• cystathionin-beta-synthasa chemie   nedostatek   genetika   MeSH
• Escherichia coli genetika   MeSH
• homocystinurie enzymologie   genetika   MeSH
• katalytická doména genetika   MeSH
• katalýza MeSH
• kvarterní struktura proteinů MeSH
• lidé MeSH
• molekulární modely MeSH
• multimerizace proteinu MeSH
• mutace * MeSH
• mutantní proteiny chemie   genetika   metabolismus   MeSH
• nízká teplota MeSH
• rozpustnost MeSH
• sbalování proteinů MeSH
• stabilita enzymů MeSH
• terciární struktura proteinů MeSH
• western blotting MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• cystathionin-beta-synthasa MeSH
• mutantní proteiny MeSH

OBJECTIVES: To estimate the frequency of the cystathionine beta-synthase deficiency caused by c.1105C>T mutation in Central Europe compared to Norway, and to examine the pathogenicity of the corresponding p.R369C mutant enzyme. STUDY DESIGN: Mutation c.1105C>T was analyzed in 600 anonymous Czech newborn blood spots. Catalytic activity and quaternary structure of the p.R369C mutant was evaluated after expression in 2 cellular systems. RESULTS: Population frequency of the c.1105C>T mutation was 0.005, predicting the birth prevalence of homocystinuria of 1:40000, which increased to 1:15500 in a model including 10 additional mutations. In Escherichia coli the p.R369C mutant misfolded, and its activity was severely reduced, and expression in Chinese hamster ovary cells enabled proper folding with activity decreased to 63% of the wild-type enzyme. This decreased activity was not due to impaired K(m) for both substrates but resulted from V(max) lowered to 55% of the normal cystathionine beta-synthase enzyme. CONCLUSIONS: The c.1105C>T (p.R369C) allele is common also in the Czech population. Although the p.R369C mutation impairs folding and decreases velocity of the enzymatic reaction, our data are congruent with rather mild clinical phenotype in homozygotes or compound heterozygotes carrying this mutation.

• MeSH
• CHO buňky enzymologie   MeSH
• Cricetulus MeSH
• cystathionin-beta-synthasa genetika   MeSH
• Escherichia coli enzymologie   MeSH
• exprese genu MeSH
• frekvence genu * MeSH
• genotyp MeSH
• homocystinurie enzymologie   epidemiologie   genetika   MeSH
• křečci praví MeSH
• lidé MeSH
• mutace genetika   MeSH
• novorozenec MeSH
• prevalence MeSH
• sbalování proteinů MeSH
• zvířata MeSH
• Check Tag
• křečci praví MeSH
• lidé MeSH
• novorozenec MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Česká republika epidemiologie   MeSH
• Názvy látek
• cystathionin-beta-synthasa MeSH

During the past 20 years, cystathionine beta-synthase (CBS) deficiency has been detected in the former Czechoslovakia with a calculated frequency of 1:349,000. The clinical manifestation was typical of homocystinuria, and about half of the 21 patients were not responsive to pyridoxine. Twelve distinct mutations were detected in 30 independent homocystinuric alleles. One half of the alleles carried either the c.833 T-->C or the IVS11-2A-->C mutation; the remaining alleles contained private mutations. The abundance of five mutant mRNAs with premature stop codons was analyzed by PCR-RFLP. Two mRNAs, c.828_931ins104 (IVS7+1G-->A) and c.1226 G-->A, were severely reduced in the cytoplasm as a result of nonsense-mediated decay. In contrast, the other three mRNAs-c.19_20insC, c.28_29delG, and c.210_235del26 (IVS1-1G-->C)-were stable. Native western blot analysis of 14 mutant fibroblast lines showed a paucity of CBS antigen, which was detectable only in aggregates. Five mutations-A114V (c.341C-->T), A155T (c.463G-->A), E176K (c.526G-->A), I278T (c.833T-->C), and W409_G453del (IVS11-2A-->C)-were expressed in Escherichia coli. All five mutant proteins formed substantially more aggregates than did the wild-type CBS, and no aggregates contained heme. These data suggest that abnormal folding, impaired heme binding, and aggregation of mutant CBS polypeptides may be common pathogenic mechanisms in CBS deficiency.

• MeSH
• alely MeSH
• cystathionin-beta-synthasa chemie   nedostatek   genetika   metabolismus   MeSH
• dítě MeSH
• dospělí MeSH
• fibroblasty MeSH
• genotyp MeSH
• hem metabolismus   MeSH
• homocystinurie enzymologie   genetika   metabolismus   MeSH
• lidé středního věku MeSH
• lidé MeSH
• messenger RNA genetika   metabolismus   MeSH
• missense mutace genetika   MeSH
• mladiství MeSH
• molekulární sekvence - údaje MeSH
• mutace genetika   MeSH
• nesmyslný kodon genetika   MeSH
• podjednotky proteinů MeSH
• polymorfismus délky restrikčních fragmentů MeSH
• terminační kodon genetika   MeSH
• vazba proteinů MeSH
• western blotting MeSH
• Check Tag
• dítě MeSH
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mladiství MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, P.H.S. MeSH
• Názvy látek
• cystathionin-beta-synthasa MeSH
• hem MeSH
• messenger RNA MeSH
• nesmyslný kodon MeSH
• podjednotky proteinů MeSH
• terminační kodon MeSH