One of the fastest growing techniques in modern medicine is the use of polymerase chain reactions (PCRs) to diagnose diseases. This method is currently being used to diagnose cancer, hereditary diseases and some infectious diseases. It was first developed in 1983, by Dr Kary Mullis, and went on to win the Nobel Prize for his discovery and work in this area. Although the technology was extremely basic to start off with it has come a long way since. The basic reaction requires no more than a heat source, a sample container and the proper primers, but the advent of the Information Age has led to the development of numerous automated and electronic PCR machines.
PCR takes a few pieces of DNA and replicates it millions of times using thermal cycling and primers. The method causes a chain reaction of replication within the original DNA, which results in it multiplying at a huge rate; as many as 40 thermal cycles may be used. PCR can also be used to analyse extremely small amounts of DNA and this has enabled the procedure to find a home in forensics, archaeology as well as medicine.
The primers which are added to the PCR sample determine what section of the DNA gets amplified. Cancer diagnosis is one of the primary uses of PCR; to diagnose leukemia, for example, the technician will mix a sample of DNA from the patient with a primer that will amplify the DNA of any leukemia cells which are present. If the DNA shows up in the results, the patient has cancer; if they do not, he or she is cancer-free. It is estimated that PCR diagnosis is at least 10,000 times more effective at early diagnosis of cancer than all other methods currently available.
This same procedure works for the diagnosis of hereditary diseases. The DNA primer which is inserted into the sample will target the specific area of the genetic code that is responsible for the suspected disease and amplify it if it is present. When it comes to detecting viral and bacterial infections, the technician will use a tissue sample from the patient and mix it with a primer that targets the viruses or bacteria which are thought to be present. PCR is so sensitive that it can detect a viral infection before the patient becomes symptomatic.
Developments and advances, in the PCR field, are occurring all the time. There are already numerous variations on the primary method and more are in testing. The primary stumbling block in expanding the use of PCR is the development of the proper primers. At the moment most diseases and conditions require specific primers. Researchers are currently working to develop primers to detect a host of problems from cancer to the genes which predispose a person towards diabetes and other problems.