Assessment of SNP-SNP interactions by using square contingency table analysis.

The evolution of SNP-SNP interactions has become an interesting field in genetic epidemiology. Most of the studies, aimed to analyze the relationship between genetic factors and disease of interest, are focused on single SNP associations. However, for quantitative traits, influenced by the interplay of environmental and more than one genetic factors, interaction between the multi factors should be taken into consideration. In this study, symmetry models for square contingency tables are applied to the cross-classified SNP-SNP interactions data. Results from a genome-wide association analysis of blood pressure are used as a prior evidence for the interacted SNPs.

Computation of the quasi-independence model for the analysis of triangular contingency tables.

Triangular contingency tables are a special class of incomplete contingency tables. Association and independence models are used to analyze such tables. This paper presents and compares some methods including the uniform association model and the quasi-independence model. These models can be described in terms of the association parameters for the analysis of triangular contingency tables having ordered categories. A computer program is developed for the analysis of quasi-independence model for positive (negative) likelihood dependence. The sign test, which is a nonparametric test of the independence against the likelihood ratio dependence, is also examined. These methods are applied to the disability ratings of stroke patients data. Effects of the structural zeros on the results are also discussed.

Effect of intravenous nitroglycerin therapy on erythrocyte antioxidant enzymes.

Intravenous nitroglycerin (GTN) has been used as an anti-ischemic agent for the therapy of unstable and post-infarction angina. Nitric oxide (NO) and S-nitrosothiols constitute the biologically active species formed via nitroglycerin bioactivation. Increased levels of reactive oxygen species can diminish the therapeutic action of organic nitrates by scavenging donated NO and oxidizing tissue thiols important in nitrate biotransformation. Studies reported here show that the red cell activity of antioxidant enzymes, catalase and glutathione peroxidase, are significantly decreased after intravenous nitroglycerin treatment. Catalase activity (739.6 +/- 92.3 k/gHb) decreased to 440.1 +/- 111.9 and 459.8 +/- 130.7 k/gHb after 1 and 24 hr GTN infusion, respectively. Similarly, glutathione peroxidase activity (5.8 +/- 1.8 U/gHb) decreased to 3.2 +/- 1.7 and 3.8 +/- 1.1 U/g Hb after 1 and 24 hr GTN infusion, respectively. The reported decrease in antioxidant enzyme activities can lead to an oxidant milieu and contribute to the generation of nitrate tolerance.