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Molecular diagnostics (MDx) is the rapidly developing and the products they encode. and platforms are playing a larger and more critical role in all areas of anatomic and clinical pathology. In the last decade or so, the clinical laboratory has seen an explosion in the available menu of tests based upon DNA and RNA analysis. The completion of the and the rapid advancement of technology to arise out of that effort has moved from the research bench to the clinical laboratory bench with swift success. For the first time in the history of the diagnostic laboratory, molecular pathology and diagnostics are extending the range of information available to physicians, pharmacists, geneticists, forensic scientists, research scientists and other healthcare professionals.

Historical and Current Examples of Molecular Diagnostics

While the ongoing SARS-CoV-2 / COVID-19 pandemic helped make molecular terms like ‘polymerase chain reaction’ (PCR), ‘false positive’ and ‘variant’ common, the field actually dates to 1949 with as a ‘molecular disease.’ However, it took decades for the scientific discipline of molecular biology to develop and become usable in the medical laboratory as a basis for disease diagnostics. MDx grew from the early days of . were critical for establishing basic knowledge on the primary sequence of various genes. DNA probes incorporating radioactive nucleotides allowed the analysis, via Southern blotting, of genomic regions, leading to the concept and application of to track variant alleles in the human genome. In 1976, were the first to make a prenatal diagnosis of α-thalassemia using MDx techniques. This diagnostic, alongside the use of RFLP to characterize sickle cell alleles, set the foundation for characterization of other genetic diseases (e.g., cystic fibrosis), as well as infectious diseases, using MDx platforms.
 
The development of led to the golden era of molecular biology and MDx, and the use of a thermostable DNA polymerase from Thermus aquaticus (i.e., Taq polymerase, ) quickly ushered this technique into the realm of laboratory medicine. With its powerful ability to exponentially amplify a target sequence, PCR allows the identification of a known mutation or sequence within hours. Not only did PCR bolster MDx in the clinical laboratory, it provided a foundation for the design and development of many variant detection schemes based on the amplification of DNA. It helped establish , depending on the basis for discriminating the allelic variants: (1) enzymatic-based methods (e.g., RFLP and oligonucleotide ligation assay), (2) electrophoretic-based methods (e.g., single-strand conformation polymorphism (SSCP), heteroduplex analyses (HAD) and denaturing gradient gel electrophoresis) and (3) solid phase-based methods (e.g., reverse dot-blot and allele-specific hybridization). While many of these methods are now infrequently used in clinical microbiology, they paved the way to current, more sophisticated methods.

After publication of the human genome draft sequence, the challenge to improve existing variant detection technologies to achieve robust, cost-effective, rapid and high-throughput analysis of genomic variation moved to the forefront of MDx. Important and critical advances continued in the world of MDx with the invention of and its numerous variations, and transcription profiling, microbiome sequencing (gut and other areas of the body), proteomics (detection of disease-specific protein profiles), pharmacogenomics, nutrigenomics, forensic medicine and CRISPR/Cas9 genomic editing.
 
Even with the advent and explosion of diverse variant detection assays, DNA sequencing is the gold standard for identification and surveillance of pathogens. This is especially true with breakthroughs in technology. However, the costs for the initial investment and the difficulties in standardization and interpretation of ambiguous results continue to place limitations on the use of NGS in clinical laboratories. Physicians and other health care professionals are now working with MDx credentialed professionals to understand the basis of One example is the use of 16S in-house assay sequencing to identify bacterial pathogens directly from tissue specimens when culture results are negative, but there is evidence of histopathologic pathogen damage.

Challenges in Molecular Diagnostics

Twenty-six years ago, the U.S. for infectious diseases. Since that time, the rapid advancement of molecular technology has been driven by : (1) automated extraction, amplification and detection platforms and (2) next-generation sequencing. As with any new advanced area, there are challenges and limitations that the laboratory medicine and public health fields must pay close attention to as these developments intersect with the care of patients and healthcare and public health policy.
 
The cost of if economic decisions limit the use of MDx to certain communities or populations. Another challenge of advanced and rapidly implemented MDx platforms is potential over- or underutilization. For example, rapid MDx platforms are often faster and more sensitive than traditional culture methods. However, the adoption of these MDx assays has been so quick that in some cases it outpaced evidence of clinical utility. The need for healthcare professional education (e.g., physicians, clinical pharmacy) is also a challenge to consider. Physicians must understand the limitations to and appropriate utilization of these technologies in order to provide cost-effective and well-informed care for their patients. 

The Medical Laboratory Needs MDx Professionals

The ability of a (or other appropriate laboratory professional) to perform molecular diagnostic testing has become critical to the laboratory medicine profession. Knowledge of methodology associated with , cancer biomarkers, inherited genetic disorders or other biomarkers is imperative for the current and future professional. The field is currently in need of well-trained medical laboratory professionals with strong biomedical science and medical laboratory science backgrounds and a thorough understanding of technologies used in assay development who can bridge the current state of practice with continuing developments in high complexity testing.
 

The best way to work in the field of MDx, command a handsome salary and learn to validate new molecular assays is to become a certified technologist in molecular biology. The American Society for Clinical Pathology (ASCP) Board of Certification (BOC) offers a . A bachelor's or master’s degree from a National Accrediting Agency for Clinical Laboratory Sciences ()-accredited program or Medical Laboratory Science (MLS) program is the fastest route to become eligible to sit for the exam. There are currently 8 NAACLS-accredited DMS programs offering a variety of options, ranging from certificates to undergraduate and graduate degrees. Although less applicable to those interested in infectious disease, there are also NAACL- accredited program in cytogenetics, and ASCP (BOC) offers a technologist in cytogenetics (CG) certification exam. Currently, there are only 4 NAACLS-accredited programs in the U.S. for cytogenetics. These degrees (DMS and CG) give graduates the skills to immediately start working in the field and validating new molecular assays to expand the molecular testing menu for more personalized patient care.

The issues surrounding the advancement of molecular diagnostics will continue to grow in the race to enhance care for individuals using genomic and metagenomic information. Those in the field need to be adaptable, analytical and ethically responsible to forge a new and exciting path of personalized medicine.