TYPES OF TESTINGS
There are many different types of genetic testing making this a very complex area that is also rapidly changing.
Confirm or refute a suspected genetic diagnosis
Traditionally genetic testing was used for either confirming or excluding a diagnosis that the doctors suspected in a patient. This type of testing could be to confirm or exclude a known chromosomal or single gene disorder. A more recent innovation is the introduction of ’gene panels’ where the genetic sequence of multiple genes associated with a specific disease (such as the large number of genes involved with cardiomyopathies or brain malformations) can be performed simultaneously and speed up the diagnostic process.
Genetic testing without a specific diagnosis
The second group of tests are performed to look for a genetic disease without knowing the exact diagnosis. This could involve a test for a chromosome abnormality (karyotype or microarray) or a gene level abnormality. The gene level abnormalities are detected by tests that are very complex and novel. These includes a test called whole exome sequencing (WES) that looks at at the DNA sequence of around 1% of our genome. In other words, the sequence of all the exons of the expressed genes of the body is sequenced and the data interpreted using computer software that looks for variations from the expected and determines the likelihood of a disease being caused by a specific DNA sequence change. Once a DNA alteration is found, careful clinical review is essential to determine if the anomaly is the likely cause of the problems in the patient.
A more complex test than WES is called whole genome sequencing where, as the name suggests, the DNA sequence of all the genes in a person is obtained. There is a higher chance of picking up an abnormality but errors caused by the large size of data generated are also possible. It is essential that expert review of the DNA data is made with the input of a clinical geneticist familiar with the patient.