Once an exciting new breakthrough and the subject of a Nobel Prize, PCR (polymerase chain reaction), is now used as routine technique in many laboratories. PCR, developed in 1983, amplifies DNA, allowing analysis of very small amounts of DNA, or damaged DNA samples. This post is a whirlwind tour of the uses of PCR – we will go into some of these in greater depth in future posts.
Diagnosis of genetic diseases
The use of PCR in diagnosing genetic disease, whether inherited genetic changes or as a result of a spontaneous genetic mutations, is becoming more common. Diseases can be diagnosed even before birth. Examples include:
- Genetic counselling – screening the parents for genetic disease before deciding on having children
- Preimplantation diagnosis – screening for genetic disease before implantation of an embryo in IVF (in vitro fertilisation)
- Screening for genetic disease before birth using tissue samples from the chorionic villus (the membranes found between the mother and unborn baby); foetal tissue from the amniotic fluid (the fluid around the unborn baby); or the small quantities of foetal DNA (DNA from the unborn baby) found in the mother’s bloodstream
- Diagnosing inherited or spontaneous diseases, either as a result of symptoms, or because of family history (e.g. Duchenne muscular dystrophy)
One of the most famous uses for PCR is in the creation of a genetic fingerprint (also known as DNA profiling) from a sample of blood or semen, or from a hair root. Much beloved by writers of detective fiction, genetic fingerprints are profiles of specific stretches of DNA (loci – commonly, 13 loci are compared) that vary from person to person. PCR also plays a role in mitochondrial DNA analysis, used for samples from hair shafts and bones when other samples are not available. The UK police has a National DNA Database.
Genetic analysis based on PCR is also used in paternity testing, and in tissue typing for organ transplantation.
Detection and diagnosis of infectious diseases
PCR can detect infectious disease before standard serological laboratory tests (tests to detect the presence of antibodies), so allowing treatment to start much earlier. Because of this, PCR is also useful for screening donated blood for infections, and is especially useful for infections that are difficult to culture in the laboratory, such as tuberculosis.
Detection of infection in the environment
PCR is used to monitor and track the spread of infectious disease within an animal or human population. PCR can also be used to detect bacterial and viral DNA in the environment, for example looking at pathogens in water supplies.
PCR is used in personalised medicine to select patients for certain treatments, for example in cancer when patients have a genetic change that makes a patient more or less likely to respond to a certain treatment.
PCR in research
PCR can be used to create copies of DNA for introduction into host organisms such as Escherichia coli in genetic engineering, and to amplify stretches of genetic material for Sanger sequencing – the Human Genome Project used PCR.
PCR can be used in analysis of gene expression, for example looking at levels of expression and when genes are switched on and off in physiological processes, including in health and disease.
PCR is used in archaeology, to identify human or animal remains, including insects trapped in amber, and to track human migration patterns; degraded DNA samples may be able to be reconstructed during the early cycles of PCR. PCR can be used to differentiate between similar organisms such as ticks, or work out relationships between different species.
Suzanne Elvidge is a freelance science, biopharma, business and health writer with more than 20 years of experience. She is editor of Genome Engineering, a blog that monitors the latest developments in genome engineering and that aims to educate (and sometimes to entertain!) and has written for a range of online and print publications including FierceBiomarkers, FierceDrugDelivery, European Life Science, the Journal of Life Sciences (now the Burrill Report), In Vivo, Life Science Leader, Nature Biotechnology, PR Week and Start-Up. She specialises in writing on pharmaceuticals, biotechnology, healthcare, science, lifestyle and green living, but can write on any topic given enough tea and chocolate biscuits. She lives just beyond the neck end of nowhere in the Peak District with her second-hand bookseller husband and two second-hand cats.