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Molecular Diagnostics

What is molecular diagnostics?

Molecular diagnostics is a branch of diagnostics that exploits the tools and knowledge of fields such as molecular biology, genetics, microbiology and biochemistry to understand the basis of disease in patients. It is chiefly based on the ability to detect the presence of and/or read the sequence of genetic material i.e. the nucleic acids DNA and RNA, and is applicable to both broad categories of medical disorders

  • Infectious diseases: Detection, identification, and quantification of infectious disease agents like bacteria, viruses, fungi and determination of antimicrobial resistance status if necessary.
  • Non-infectious diseases: Detection of qualitative and quantitative changes in human genetic material either inherited (e.g. Disorders such as Sickle Cell Anemia and Thalassemia) or acquired (e.g. Cancers)

In addition to primary diagnosis of disease conditions (Prader Willi, Down Syndrome, Usher) and prenatal diagnostics (Thalassemia, Trisomies), other medical areas also fall under the broad category of molecular diagnostics.
These include

  • Guidance of therapy (e.g. detection of a particular mutation in a gene associated with neonatal diabetes can lead to change in treatment for the baby from two daily insulin injections to oral sulfonylurea therapy)
  • Monitoring of therapy (e.g. monitoring drop in viral loads after anti-viral treatment and monitoring of residual disease after bone marrow transplant)
  • Companion diagnostics / Pharmacogenetic testing: Genetic testing to determine eligibility for herceptin treatment in breast cancer or for determination of warfarin dosage in cardiac procedures
  • Predictive testing/ Prognostics (e.g. BRCA1/2 mutations are linked to high predisposition to breast and ovarian cancers, mutations in TOP2A determines survival rates in breast cancer)
  • Identity testing (e.g. matching of donor and recipient during organ transplantation)

What are the advantages of molecular diagnostics?

Molecular diagnostics directly looks for the causative agent (in the case of infectious disease) or variations in genetic patterns (in case of non-infectious diseases) rather than looking at the effects of the disease. This allows more sensitive, specific and rapid detection, and in some cases allows detection where none was possible before. This can be illustrated through these examples

For infectious diseases

Rapid identification of the causative agent of a disease whether it is a bacterium, virus, fungus or protozoan with an indication on the level of infection, and information on what drugs it will be sensitive and resistant to. This allows the doctor to act on that information within hours rather than days as they do currently. Particularly important in ICU infections where it can mean the difference between life and death, not to mention the cost of increased stay in the ICU.

For cancer

Detection of predictive risk (e.g in familial cancers which can then enable different levels of intervention based on the risk), selection of appropriate therapy and dosing based on the molecular type of the cancer and the genetic makeup of the patient (i.e. higher success of chemotherapy and lower side effects).

For transplantation

Rapid matching of donors to recipients. This can be done more accurately and within 2-3 hours as against the 3 days it takes currently. Better chance of survival with a better match, and the ability to utilize cadaveric donors who are currently being wasted.

For pre-natal and pre-implantation diagnostics

Diagnosis of amniotic or chorionic villus samples, or even non-invasive diagnosis of cell free fetal DNA from maternal blood, from pregnant women who are at high risk to have children with anomalies like Down Syndrome, etc; especially useful in families that have a genetic history of disorders, or who have lost a child or sibling or who are at a relatively advanced age at the time of pregnancy. Pre-implantation genetic diagnosis goes a step further by carrying out the fertilization in vitro (externally), checking for anomalies, and only implanting the embryo if no genetic defects are detected.

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