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For more than a quarter century, the polymerase chain reaction (PCR)—in which a specific region of DNA is amplified in a repeating cycle—has served as an invaluable technique for measuring gene expression. In particular, researchers are relying increasingly on real-time PCR, which detects the products of the PCR cycle as they occur. “Real-time PCR has proven to be sensitive and specific enough for testing clinical specimens,” says Shirley Welsh, senior director of PCR instruments at Life Technologies in Carlsbad, Calif. “PCR instruments are currently being used by researchers to better understand cancer.” The Oncotype DX breast cancer assay, for instance, employs real-time PCR to quantify the expression of 21 genes (16 cancer genes and five control genes).
In clinical science, real-time PCR continues to replace existing culturebased methods. “Moving to real-time PCR will provide clinicians with faster results and very specific information,” Welsh says.
Examples of researchers exploring real-time PCR in diagnostics already exist. For example, an e-publication in Physiological Genomics, posted on May 18, 2010, described how researchers used this technology to study microRNAs (miRNAs) related to chronic heart failure, and found that the “identified miRNAs might have a potential diagnostic and/or prognostic use in” chronic heart failure. Another e-publication in Diagnostic Microbiology and Infectious Disease, published online on May 10, 2010, documented the authors’ use of real-time PCR to detect Dientamoeba fragilis, which is a parasite that infects the large intestine of people around the world. The authors of the study concluded: “The evaluated real-time PCR assay represents an effective tool to obtain both an accurate diagnosis and a reliable epidemiologic picture of Dientamoebiasis.”
The key to utilizing such technology in the future depends on the development of easy-to-use and reliable instruments. As an example, Life Technologies recently introduced its research use– only ViiA 7 Real-Time PCR System. This system is sensitive enough to detect a single copy of starting genetic material. Such technology will simplify the measurement of a range of chromosomal features that are often explored in health research, including changes in the number of copies of a specific gene (better known as copy-number variation) and the detection of changes in single bases of DNA, or single nucleotide polymorphisms. To use this tool in clinical diagnostics, however, it must first gain regulatory approval.
PCR, a now common research tool, will surely add a higher level of specificity to a range of clinical tests in the future. Rather than sending out samples to be cultured, physicians will someday use real-time PCR to provide patients with accurate and fast answers about their health.