Overview

Genetic testing involves the determination of whether a particular DNA sequence is present or absent in a patient's sample. In some cases, tests are designed to determine the presence or absence of known mutations (mutation testing), whereas in other cases the sample is screened for any deviation from the normal DNA sequence (mutation scanning).

There exist a large number of approaches for both mutation testing and mutation scanning. The situation is further complicated by the existence of many different types of genetic mutation (point mutations, deletions large and small, gene rearrangements, duplications, triplet repeat expansions), each of which may require different testing or scanning technologies. There is no ''gold standard'' testing or scanning method which will detect all possible mutation types. Although many genetics tests are qualitative in nature (presence or absence of a DNA sequence), some are quantitative. These involve either the measurement of the number of copies of a gene or part of a gene (to test for duplications or deletions) or the measurement of the number of copies of the repeated sequence in short repeated stretches of DNA which may be located adjacent to or within genes. Preparation of certified reference materials for molecular genetic testing had until recently not been attempted, and there are as yet no CRMs available in this field. Currently, molecular genetics tests are validated using reference materials which are often derived from research laboratories. These materials are deemed to be valid on the basis that an expert laboratory has determined that the material contains (or does not contain) a particular mutation. The materials are usually distributed on an informed peer-to-peer basis in response to personal requests made to the expert laboratory. There are few instances of organized distribution of genetic reference materials which have been validated in a methodical way by more than one laboratory. One exception involves the materials distributed for the purposes of external quality assurance (EQA) schemes. These materials are routinely validated by two laboratories before distribution, and the consensus result obtained by scheme participants provides further validation. However, the amount of such materials remaining in participating laboratories after completion of EQA schemes is usually small, perhaps only sufficient for a few assays. For quantitative tests, this may be sufficient to calibrate in-house materials which can then be used as reference samples and run with each batch of tests. Qualitative tests, however, require positive and negative control material which can be run with each batch of test samples. It is not unusual for a laboratory to test many hundreds of samples without ever encountering a positive result.

Thus a continuing supply of reference material which is certified to give a positive result is required for each test. The material left over from EQA schemes cannot fill this requirement. Furthermore, many laboratories are beyond the reach of the EQA schemes which are currently in place and have no access to these materials. These laboratories are likely to be the ones most in need of external validation of their tests through the use of appropriate reference materials. The fact that many laboratories fail to provide correct mutation detection in the ongoing European EQAs[3] further stresses the need for the availability of certified RMs.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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