Evaluating predictive pharmacogenetic signatures of adverse events in colorectal cancer patients treated with fluoropyrimidines

The potential clinical utility of genetic markers associated with response to fluoropyrimidine treatment in colorectal cancer patients remains controversial despite extensive study. Our aim was to test the clinical validity of both novel and previously identified markers of adverse events in a broad clinical setting. We have conducted an observational pharmacogenetic study of early adverse events in a cohort study of 254 colorectal cancer patients treated with 5-fluorouracil or capecitabine. Sixteen variants of nine key folate (pharmacodynamic) and drug metabolising (pharmacokinetic) enzymes have been analysed as individual markers and/or signatures of markers. We found a significant association between TYMP S471L (rs11479) and early dose modifications and/or severe adverse events (adjusted OR = 2.02 [1.03; 4.00], p = 0.042, adjusted OR = 2.70 [1.23; 5.92], p = 0.01 respectively). There was also a significant association between these phenotypes and a signature of DPYD mutations (Adjusted OR = 3.96 [1.17; 13.33], p = 0.03, adjusted OR = 6.76 [1.99; 22.96], p = 0.002 respectively). We did not identify any significant associations between the individual candidate pharmacodynamic markers and toxicity. If a predictive test for early adverse events analysed the TYMP and DPYD variants as a signature, the sensitivity would be 45.5 %, with a positive predictive value of just 33.9 % and thus poor clinical validity. Most studies to date have been under-powered to consider multiple pharmacokinetic and pharmacodynamic variants simultaneously but this and similar individualised data sets could be pooled in meta-analyses to resolve uncertainties about the potential clinical utility of these markers

A Comprehensive Association Analysis of Homocysteine Metabolic Pathway Genes in Singaporean Chinese with Ischemic Stroke

10.1371/journal.pone.0024757PLoS ONE69

Role of C677T and A1298C MTHFR, A2756G MTR and -786 C/T eNOS Gene Polymorphisms in Atrial Fibrillation Susceptibility

Hyperhomocysteinemia has been suggested to play a role in the NonValvular Atrial Fibrillation (NVAF) pathogenesis. Polymorphisms in genes coding for homocysteine (Hcy) metabolism enzymes may be associated with hyperhomocysteinemia and NVAF.456 NVAF patients and 912 matched controls were genotyped by an electronic microchip technology for C677T and A1298C MTHFR, A2756G MTR, and -786C/T eNOS gene polymorphisms. Hcy was determined by an immunoassay method.The genotype distribution of the four polymorphisms as well as genotype combinations did not differ in patients and controls. Hcy was higher in patients than in controls (15.2, 95%CI 14.7–15.7 vs 11.3, 95%CI 11.0–11.6 µmol/L; p<0.0001). In both populations, a genotype-phenotype association (p<0.0001) between Hcy and C677T MTHFR polymorphism was observed; in controls a significant (p = 0.029) association between tHcy and −786C/T eNOS polymorphism was also observed. At the multivariate analysis the NVAF risk significantly increased in the upper quartiles of Hcy compared to the lowest: OR from 2.8 (1.68–4.54 95%CI) in Q2 to 12.9 (7.96–21.06 95%CI) in Q4. or in combination

S-adenosylmethionine and S-adenosylhomocysteine levels in the aging brain of APP/PS1 Alzheimer mice

Hyperhomocysteinemia and factors of homocysteine metabolism, S-adenosylhomocysteine (AdoHcy) and S-adenosylmethionine (AdoMet), may play a role in Alzheimer’s disease (AD). With liquid-chromatography-tandem-mass-spectrometry AdoMet and AdoHcy were determined in brains of 8- and 15-month-old APP/PS1 Alzheimer mice, and their possible roles in AD brains investigated. The finding that AdoMet levels do not differ between the genotypes in (young) 8-month-old mice, but are different in (older) 15-month-old APP/PS1 mice compared to their wild-type littermates, suggests that alterations in AdoMet are a consequence of AD pathology rather than a cause. During aging, AdoMet levels decreased in the brains of wild-type mice, whereas AdoHcy levels diminished in both wild type and APP/PS1 mice. The finding that AdoMet levels in APP/PS1 mice are not decreased during aging (in contrast to wild-type mice), is probably related to less demand due to neurodegeneration. No effect of the omega-3 fatty acid docosahexaenoic acid (DHA) or cholesterol-enriched diets on AdoMet or AdoHcy levels were found

Consensus recommendations for the diagnosis, treatment and follow-up of inherited methylation disorders

Inherited methylation disorders are a group of rarely reported, probably largely underdiagnosed disorders affecting transmethylation processes in the metabolic pathway between methionine and homocysteine. These are methionine adenosyltransferase I/III, glycine N-methyltransferase, S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. This paper provides the first consensus recommendations for the diagnosis and management of methylation disorders. Following search of the literature and evaluation according to the SIGN-methodology of all reported patients with methylation defects, graded recommendations are provided in a structured way comprising diagnosis (clinical presentation, biochemical abnormalities, differential diagnosis, newborn screening, prenatal diagnosis), therapy and follow-up. Methylation disorders predominantly affect the liver, central nervous system and muscles, but clinical presentation can vary considerably between and within disorders. Although isolated hypermethioninemia is the biochemical hallmark of this group of disorders, it is not always present, especially in early infancy. Plasma S-adenosylmethionine and S-adenosylhomocysteine are key metabolites for the biochemical clarification of isolated hypermethioninemia. Mild hyperhomocysteinemia can be present in all methylation disorders. Methylation disorders do not qualify as primary targets of newborn screening. A low-methionine diet can be beneficial in patients with methionine adenosyltransferase I/III deficiency if plasma methionine concentrations exceed 800 μmol/L. There is some evidence that this diet may also be beneficial in patients with S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. S-adenosylmethionine supplementation may be useful in patients with methionine adenosyltransferase I/III deficiency. Recommendations given in this article are based on general principles and in practice should be adjusted individually according to patient's age, severity of the disease, clinical and laboratory findings

Molecular genetic analysis of hyperhomocysteinemia.

Contains fulltext : 30131_molegeano.pdf (publisher's version ) (Open Access)Homocysteine is a intermediary product of protein metabolism. A high concentration of homocysteine in the blood is associated with a higher risk of cardiovascular disease, including venous thrombosis. Homocysteine levels are in part determined by genetic factors and vitamin intake (such as vitamin B12). The main goal of the presented research was to identify genetic factors (polymorphisms) that affect homocysteine levels and to assess if these polymorphisms also increased the risk of recurrent venous thrombosis. In addition, we evaluated vitamin B12 as a risk factor of recurrent venous thrombosis. We investigated a polymorphism in the catechol-O-methyltransferase gene, which is involved in so-called 'transmethylation reactions', in relation to homocysteine levels. Individuals carrying this polymorphism had higher homocysteine levels than subjects that did not carry this variant. In addition, this polymorphism was more common in recurrent venous thrombosis cases than the general population. This supports the hypothesis that high homocysteine reflects a disturbed transmethylation, which increases venous thrombosis risk. We also developed a method to study metabolites in the blood that report on the ability of our body to perform transmethylation reactions. It appeared that the way the blood samples were stabilized was of great importance for the reliability of our method. Future studies will have to point out whether a disturbed transmethylation is involved in the aetiology of venous thrombosis. Finally, we show that a low vitamin B12 status, which is a cause of high homocysteine levels, is associated with an increased risk of recurrent venous thrombosis. Measuring methylmalonic acid, a marker of intracellular vitamin B12 availability, seems more suitable for measuring vitamin B12 status than plasma vitamin B12 itself.RU Radboud Universiteit Nijmegen, 11 januari 2007Promotor : Hermus, A.R.M.M. Co-promotores : Heijer, M. den, Blom, H.J.165 p

Associations of common polymorphisms in the thymidylate synthase, reduced folate carrier and 5-aminoimidazole-4-carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase genes with folate and homocysteine levels and venous thrombosis risk.

Item does not contain fulltextBACKGROUND: Folate is important in purine and thymidylate synthesis and, via homocysteine remethylation, facilitates S-adenosylmethionine-dependent transmethylation. Low folate availability leads to hyperhomocysteinemia, which is a risk factor for arterial vascular disease and venous thrombosis. Genetic variation in folate-metabolizing genes may affect folate availability and hence confer a greater risk of venous thrombosis. METHODS: We genotyped the thymidylate synthase (TYMS) 28-bp repeat and 6-bp deletion, and the reduced folate carrier (RFC1) 80G>A and AICAR transformylase/inosine monophosphate (IMP) cyclohydrolase (ATIC) 346C>G polymorphisms in population-based controls (n=431), and assessed their effect on plasma total homocysteine (tHcy), and serum and red blood cell (RBC) folate. We investigated the associations between these variants and disease risk in a retrospective case-control study on recurrent venous thrombosis (n=173) as well. RESULTS: None of the genotypes, alone or in combination, were associated with major changes in tHcy. However, the TYMS 28-bp repeat was associated with serum and RBC folate levels. We found no evidence that the genetic variants studied were associated with recurrent venous thrombosis risk. CONCLUSIONS: The TYMS 28-bp repeat and 6-bp deletion, and RFC1 80G>A and ATIC 346C>G polymorphisms are not associated with tHcy, but we did observe an association between the TYMS 28-bp repeat and serum and RBC folate in a general population. None of the polymorphisms was associated with recurrent venous thrombosis risk

Genetic determinants of plasma total homocysteine.

Item does not contain fulltextHyperhomocysteinemia (Hhcy) is an established risk factor for various pathologies including arterial vascular disease and venous thrombosis, congenital malformations and other pregnancy complications, and dementia. Homocysteine remethylation, transsulfuration, and export to the blood/extracellular compartment determine homocysteine concentrations. Any disturbance in these routes may lead to Hhcy and potentially increase risk of disease. In this report, we aim to review all known polymorphisms involved in homocysteine and B-vitamin metabolism that have been assessed for their effect on tHcy. In the last section, we summarize the polymorphisms, for which the obtained data provides evidence for their involvement in Hhcy at the population level, and discuss how to continue our search for genetic determinants of tHcy