Molecular diagnostics
[1] From 2002 onwards, the HapMap Project aggregated information on the one-letter genetic differences that recur in the human population—the single nucleotide polymorphisms—and their relationship with disease.
[2]: ch 37 In 2012, molecular diagnostic techniques for Thalassemia use genetic hybridization tests to identify the specific single nucleotide polymorphism causing an individual's disease.
[2]: foreword Miniaturisation into a single handheld device can bring medical diagnostics into the clinic and into the office or home.
[18] Automation and sample barcoding maximise throughput and reduce the possibility of error or contamination during manual handling and results reporting.
[2]: ch 39 Because molecular diagnostics methods can detect sensitive markers, these tests are less intrusive than a traditional biopsy.
[24] Molecular diagnostic tests vary widely in sensitivity, turn around time, cost, coverage and regulatory approval.
[25] Benefits Conventional prenatal tests for chromosomal abnormalities such as Down Syndrome rely on analysing the number and appearance of the chromosomes—the karyotype.
[28] Advances in molecular biology have helped show that some syndromes that were previously classed as a single disease are actually multiple subtypes with entirely different causes and treatments.
Molecular diagnostics can help diagnose the subtype—for example of infections and cancers—or the genetic analysis of a disease with an inherited component, such as Silver-Russell syndrome.
[34] Genetic identification can be swift; for example a loop-mediated isothermal amplification test diagnoses the malaria parasite and is rugged enough for developing countries.
[36] Molecular diagnostics are also used to understand the specific strain of the pathogen—for example by detecting which drug resistance genes it possesses—and hence which therapies to avoid.
These technologies generally can be grouped into three approaches: polymerase chain reaction (PCR), hybridization, and next-generation sequencing (NGS).
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.
For instance, Qiagen therascreen,[49] Roche cobas[50] and Biomerieux THxID[51] have developed FDA approved PCR tests for detecting lung, colon cancer and metastatic melanoma mutations in the KRAS, EGFR and BRAF genes.
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.
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.
Their technology can inform patients to seek chemotherapy when necessary by examining the RNA expression levels in breast cancer biopsy tissue.
Currently, research in cancer diagnostics are developing fast with goals for lower cost, less time consumption and simpler methods for doctors and patients.
