The human body is made up of molecules that fit generally into the categories of DNA, RNA, proteins, sugars, salts, fats and water. These last four groups are generally governed by the proteins in the human body and become imbalanced as a result of protein dysfunction. Technological strategies, developed as a result of the Human Genome Project, can rapidly and almost comprehensively scan through the DNA, RNA and protein molecules of the human body in order to identify differences between individuals with a disorder versus those without. These strategies are collectively known as the “-omics.”
Transcriptomics refers to the comprehensive scanning of the nearly fifty thousand currently known genes that are transcribed into RNA molecules from the three-billion-letter human genome. Each cell utilizes (expresses) different genes at different times in its development and under different physiological conditions. In general, tissues express similar sets of genes that can be used to identify those tissues in the absence of any other information. For example, the brain expresses about thirty percent of all of the known genes; those specific transcripts are different from the transcribed genome in the heart. We can therefore define molecular signatures based on expression profiles, and these profiles can then be used to automatically separate normal cells or tissues into their correct category.