Biomarker discovery and validation.

Currently available biomarkers, such as those used to diagnose myocardial infarction (e.g., cardiac troponins), were identified in the course of targeted physiologic studies. Similarly, basic investigation of diseases has largely been characterized by studies of isolated molecules in cellular systems. Advances in genomics technologies, however, are beginning to permit characterization of global alterations associated with disease conditions and, in the process, identification of novel biomarkers and pathways. Laterza et al.(1) used such a global survey, and in this issue of Clinical Chemistry they describe their discovery of potential new markers related specifically to brain injury. Now begins the long road toward validation of these markers in clinically relevant human cohorts. Although no serum biomarkers of brain injury for conditions such as stroke are in clinical use, they could ultimately prove to be of enormous clinical usefulness to complement physical and radiologic examinations, both of which can be ambiguous during acute presentations. Of the multiple genomics applications, perhaps none has garnered more recent attention for biomarker discovery than proteomics. Proteomics offers unique insight into disease because proteins and their bioenzymatic functions largely determine the phenotypic diversity that can arise from a set of common genes. Posttranslational modifications help regulate structure, function, localization, maturation, and turnover of proteins. Because the entire complement of expressed proteins in their various forms can rapidly change in response to environmental cues, the proteome represents the unique ensemble of proteins that reflects the state of the cell or group of cells at a given time, in a particular context under particular stimuli. Thus, the proteome is highly dynamic, in contrast to the stability of the genome. The one gene–one protein dictum, now no longer tenable, had led few to anticipate the immense magnitude and complexity of the resulting proteome. This complexity, however, is the basis of …