The advent of microarray technology has led to genome-wide interrogation of transcript abundance. Numerous studies have characterised variation in human gene expression associated with cell and tissue type, environmental conditions or disease and these have led to a better understanding of biological pathways. For clinical purposes, gene expression signatures have been useful to classify tumours [1,2], to identify diagnostic markers [3] or patient groups that benefit from therapies [4] and to understand infectious disease processes [5].
