Common forms of cardiovascular diseases are exceptionally complex, where several genetic and life style/environmental factors are involved. The discovery of different risk factors will be crucial for prevention of these high mortality diseases. It has become clear that in case of complex phenotypes, analyzing the individual components of a system is probably not sufficient, because components interact with each other and these interactions differ in disease state. Thus, the system-based approaches, simultaneous analysis of different datasets in combination with computational and statistical tools, will probably have more potential to address complex phenotypes. In parallel with genomics and transcriptomics studies, metabolomic studies have broaden our understanding of cardiovascular phenotypes and have created possibility to find new biomarkers for disease risk prediction. The results obtained in recent study indicate a new metabolic pathway linking dietary lipid phosphatidylcholine intake, intestinal bacteria and liver metabolism to generate metabolite trimethylamine N-oxide (TMAO) that promotes the build-up of arterial plaque and cardiovascular disease. In this proposal we aim to study the role of TMAO in multiple traits related to cardiovascular diseases. We will measure the TMAO changes using a well-characterized cardiovascular targeted samples and detect phenotypes where the elevated level of TMAO could be used for prediction of disease risk. The second part of the project aims to identify genetic factors that are related to changes in TMAO level using the systems-based approach. We will integrate genetic, expression and metabolic information in order to define genes or genetic factors which are involved with the changes of TMAO concentration and hence in regulation of cholin metabolism. The proposed study will help to understand TMAO role in complex metabolic and cardiovascular disorders.