Twenty years ago, the Human Genome Project was initiated aiming to uncover the genetic factors of human diseases and to develop new strategies for diagnosis, treatment and prevention. The successful sequencing of the human genome and the following coordinated efforts, such as the HapMap project (1), genome-wide association studies (2) and the cancer genome projects (3), have resulted in the discovery of many disease-associated genes. However, our understanding of molecular mechanisms is still largely incomplete for the majority of diseases, which are multi-factorial diseases resulting from the combination of various genetic and environmental factors. There must be inherent relationships among these factors for the etiology and pathogenesis, and they may be characterized by considering the molecular networks involving these factors. The analysis of network–disease associations, in addition to gene–disease associations, would better clarify the molecular mechanisms of diseases and help develop new drugs and treatments.
