There are many potential pitfalls that lie in the way of researchers on the route from the discovery of a mutation in human DNA that codes for a pharmacologically important protein to the development of a clinically useful pharmacogenetic test. Very few such tests have been developed as yet, but a considerable number seem likely to be found useful over the next decade in guiding the treatment of patients with cancer, asthma, depression, hypertension, and pain.
In the development of new pharmacogenetic tests, as for any other clinically applied test, assay sensitivity, specificity, and positive predictive value will have to be scrutinized rigorously. In addition, the reliability of DNA testing in terms of intra- and interday variability and the rigor of assays when applied to multiple DNA samples will have to be demonstrated almost more carefully than it would be for routine assays for serum chemistries or hematology. This is because there are significant societal pressures that insist upon the accuracy of a diagnostic test that informs a physician and a patient about an individual's genetic makeup. The requirement for robust tests has not prevented any other technology from entering clinical practice though, and already a number of array-based genetic tests are available that are able to diagnose genotypes simultaneously at a relatively large number of loci.
When the technical barrier of developing tests with adequate sensitivity, specificity, and reproducibility is overcome, it seems very likely that the practice of medicine will evolve so that individual patients can be treated for their diseases with appropriately individualized doses of medicines, or indeed different medicines directed at specific therapeutic targets, based on their genotype or phenotype.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.