PCR technology has become an essential research and diagnostic tool for improving human health and quality of life. PCR technology allows scientists to take a specimen of genetic material, even from just one cell, copy its genetic sequence over and over, and generate a test sample sufficient to detect the presence or absence of a specific virus, bacterium or any particular sequence of genetic material. Medical research and clinical medicine are benefiting from PCR technology mainly in two areas:
- Detection of infectious organisms, including the viruses that cause AIDS and hepatitis, and other microorganisms that affect women's health and cause tuberculosis.
- Detection of genetic variations, including mutations, in human genes
PCR and Infectious Disease
PCR technology facilitates the detection of DNA or RNA of pathogenic organisms and, as such, is the basis for a broad range of clinical diagnostic tests for various infectious agents, including viruses and bacteria. These PCR-based tests have several advantages over traditional antibody-based diagnostic methods that measure the body's immune response to a pathogen. In particular, PCR-based tests are able to detect the presence of pathogenic agents earlier than serologically-based methods, as patients can take weeks to develop antibodies against an infectious agent. Earlier detection of infection can mean earlier treatment and an earlier return to good health.
Capitalizing on its exquisite sensitivity, scientists have also developed PCR-based tests designed to quantify the amount of virus in a person's blood ('viral load') thereby allowing physicians to monitor their patients' disease progression and response to therapy. Viral load assessment before, during and after therapy has tremendous potential for improving the clinical management of diseases caused by viral infection, including AIDS and hepatitis.
PCR-based diagnostics tests are available for detecting and/or quantifying several pathogens, including:
- HIV-1, which causes AIDS
- Hepatitis B and C viruses, which can lead to liver cancer
- Human Papillomavirus, which can cause cervical cancer
- Chlamydia trachomatis, which can lead to infertility in women
- Neisseria gonorrhoeae, which can lead to pelvic inflammatory disease in women
- Cytomegalovirus, which can cause life threatening disease in transplant patients and other immunocompromised people, including HIV-1/AIDS patients
- Mycobacterium tuberculosis, which in its active state causes cough and fatigue and can lead to tissue damage of infected organs
PCR and Blood Screening
Since the 1970s serological tests have been used to screen donated blood samples for the presence of infectious agents. Nevertheless, a small risk of viral transmission remains primarily due to the failure of such screening tests to identify recently infected donors during the "window period" - the time delay post-infection in which the body develops an immune response to the infectious agent. Tests using PCR nucleic acid amplification testing (NAT) technology detect the actual virus. Experts believe that including such tests in blood screening programs could provide an added measure of protection by detecting viral infection at an earlier stage.
Highly sensitive PCR-based tests are available for detecting early markers of HIV-1, hepatitis B and hepatitis C infection, namely viral DNA or RNA, in blood. These tests are helping to narrow the "window period" resulting in improved blood safety. Benefits of using PCR technology to monitor the world's blood supply include:
- A decrease in the waiting period or "window period" during which the infectious agent is undetectable by traditional screening technologies that rely on the formation of antibodies
- The ability to perform comprehensive and combined blood screening for several pathogens, including hepatitis C, hepatitis B and HIV-1. Combination PCR-based tests incorporated into blood donor screening programs could dramatically reduce the risk of virus transmission1
1Blood Safety in the New Millennium, published by the American Association of Blood Banks, 2001
PCR and Genetic Testing
Because PCR technology can be used to easily distinguish among the tiny variations in DNA that make people genetically unique, the technology is leading to new methods for genetic testing. Available today for diagnosing a handful of disorders, including Cystic Fibrosis, in the future PCR technology may be used in predictive tests-methods for finding out who is predisposed to common disorders, such as heart disease and many cancers.
Roche is developing new molecular-based tests in disease predisposition, cancer screening and cancer therapy selection, and pharmacogenetics, a process that determines how a person responds to a drug based on his or her genetic makeup. Genetic analysis can provide information as to whether an individual has the correct metabolic pathway to metabolize a particular drug, or even produces the correct genetic target for the drug. As a result, physicians will not have to rely on trial and error when prescribing therapies to patients. Instead, doctors will have a clearer understanding of which treatments will work best for patients, contributing to better therapies, a substantial savings in the cost of medications, and in the enhancement or improvements in quality of life for patients.