Molecular diagnostics
Molecular diagnostics is a collection of techniques used to analyze
By analysing the specifics of the patient and their disease, molecular diagnostics offers the prospect of personalised medicine.[4] These tests are useful in a range of
History
The field of molecular biology grew in the late twentieth century, as did its clinical application. In 1980,
During the 1990s, the identification of newly discovered genes and new techniques for DNA sequencing led to the appearance of a distinct field of molecular and genomic laboratory medicine; in 1995, the Association for Molecular Pathology (AMP) was formed to give it structure. In 1999, the AMP co-founded The Journal of Medical Diagnostics.
As the commercial application of molecular diagnostics has become more important, so has
Techniques
Development from research tools
The industrialisation of molecular biology assay tools has made it practical to use them in clinics.
Laboratory processes need to adhere to regulations, such as the
Automation and sample barcoding maximise throughput and reduce the possibility of error or contamination during manual handling and results reporting. Single devices to do the assay from beginning to end are now available.[15]
Assays
Molecular diagnostics uses in vitro
Because molecular diagnostics methods can detect sensitive markers, these tests are less intrusive than a traditional
Benefits
Prenatal
Conventional prenatal tests for
Treatment
Some of a patient's
Infectious disease
Molecular diagnostics are used to identify infectious diseases such as
Disease risk management
A patient's genome may include an inherited or random mutation which affects the probability of developing a disease in the future.
Cancer
Cancer is a disease with excessive molecular causes and constant evolution. There's also heterogeneity of disease even in an individual. Molecular studies of cancer have proved the significance of driver mutations in the growth and metastasis of tumors.[45] Many technologies for detection of sequence variations have been developed for cancer research. These technologies generally can be grouped into three approaches: polymerase chain reaction (PCR), hybridization, and next-generation sequencing (NGS).[22] Currently, a lot of PCR and hybridization assays have been approved by FDA as in vitro diagnostics.[46] NGS assays, however, are still at an early stage in clinical diagnostics.[47]
To do the molecular diagnostic test for cancer, one of the significant issue is the DNA sequence variation detection. Tumor biopsy samples used for diagnostics always contain as little as 5% of the target variant as compared to wildtype sequence. Also, for noninvasive applications from peripheral blood or urine, the DNA test must be specific enough to detect mutations at variant allele frequencies of less than 0.1%.[22]
Currently, by optimizing the traditional PCR, there's a new invention, amplification-refractory mutation system (ARMS) is a method for detecting DNA sequence variants in cancer. The principle behind ARMS is that the enzymatic extension activity of DNA polymerases is highly sensitive to mismatches near the 3' end of primer.[22] Many different companies have developed diagnostics tests based on ARMS PCR primers. For instance, Qiagen therascreen,[48] Roche cobas[49] and Biomerieux THxID[50] have developed FDA approved PCR tests for detecting lung, colon cancer and metastatic melanoma mutations in the KRAS, EGFR and BRAF genes. Their IVD kits were basically validated on genomic DNA extracted from FFPE tissue.
There are also microarrays that utilize hybridization mechanism to diagnose cancer. More than a million of different probes can be synthesized on an array with Affymetrix's Genechip technology with a detection limit of one to ten copies of mRNA per well.[22] Optimized microarrays are typically considered to produce repeatable relative quantitation of different targets.[51] Currently, FDA have already approved a number of diagnostics assays utilizing microarrays: Agendia's MammaPrint assays can inform the breast cancer recurrence risk by profiling the expression of 70 genes related to breast cancer;[52] Autogenomics INFNITI CYP2C19 assay can profile genetic polymorphisms, whose impacts on therapeutic response to antidepressants are great;[53] and Affymetrix's CytoScan Dx can evaluate intellectual disabilities and congenital disorders by analyzing chromosomal mutation.[54]
In the future, the diagnostic tools for cancer will likely to focus on the Next Generation Sequencing (NGS). By utilizing DNA and RNA sequencing to do cancer diagnostics, technology in the field of molecular diagnostics tools will develop better. Although NGS throughput and price have dramatically been reduced over the past 10 years by roughly 100-fold, we remain at least 6 orders of magnitude away from performing deep sequencing at a whole genome level.[22] Currently, Ion Torrent developed some NGS panels based on translational AmpliSeq, for example, the Oncomine Comprehensive Assay.[55] They are focusing on utilizing deep sequencing of cancer-related genes to detect rare sequence variants.
Molecular diagnostics tool can be used for cancer risk assessment. For example, the BRCA1/2 test by Myriad Genetics assesses women for lifetime risk of breast cancer.[22] Also, some cancers are not always employed with clear symptoms. It is useful to analyze people when they do not show obvious symptoms and thus can detect cancer at early stages. For example, the ColoGuard test may be used to screen people over 55 years old for colorectal cancer.[56] Cancer is a longtime-scale disease with various progression steps, molecular diagnostics tools can be used for prognosis of cancer progression. For example, the OncoType Dx test by Genomic Health can estimate risk of breast cancer. Their technology can inform patients to seek chemotherapy when necessary by examining the RNA expression levels in breast cancer biopsy tissue.[57]
With rising government support in DNA molecular diagnostics, it is expected that an increasing number of clinical DNA detection assays for cancers will become available soon. Currently, research in cancer diagnostics are developing fast with goals for lower cost, less time consumption and simpler methods for doctors and patients.
See also
- Molecular medicine (the broader field of the molecular understanding of disease)
- Molecular pathology
- Laboratory Developed Test
- Pathogenesis
- Pathogenomics
- Pathology
- Precision medicine
- Personalized medicine
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