Types of Genetic Testing

In the retina community we hear a lot more these days about genetic tests and their impact on all of the community including medical professionals, researchers and most especially, patients. The progress in this technology over the past twenty years has been remarkable and indeed it has advanced year on year and far more quickly than many other forms of technology, including information and mobile technology. From over a billion dollars in the late 1990s to just hundreds these days – tests are now more accessible than ever. However inequalities remain and access is not universal.
In a recent survey of patient members Retina International learnt that of 62% of respondents had a genetic test, 53% accessed their test through a research project. This is unfair as not all patients can participate in research studies and it is unsustainable for research institutions to be placed in a position where they are required to plug this gap in access. There are also challenges in accessing testing through medical insurance due to lack of systematic cover. In this case it is often only those who can afford genetic testing that gain access to these services.

Today genetic tests are faster and more accurate and they provide a wealth of knowledge leading to greater understanding of some of the most complex REDs and IRDs. Policy makers must understand the burden of uncertainty that is placed on patients when these tests are not available to all those who need this service.

 It is this inequality in access that is of great concern to Retina International and its member’s organisations. It is also something that is of concern to medical professionals and research scientists in the retina space. This is because when large portions of the population are not being tested their conditions will not be recorded in databases (registers) resulting in affected individuals not being included in clinical trials, scientists not having access to the global picture and fundamentally patients not being informed. As a community we must work hard to change this reality through better understanding of the testing and the impact it can have not only on the delivery of better healthcare and more targeted research but also and importantly for the patient themselves to make informed choices in their life.

Genetic tests examine human DNA, RNA, or proteins to detect abnormalities related to IRDs. Tests can directly examine for abnormalities of chromosomes (cytogenetic testing), examine the DNA or RNA for genetic defects, and they can examine the protein products of genes which is called biochemical testing.
It is very important to note that when considering genetic testing, physicians understand the difference between clinically available tests and “research only” tests.
Below we have listed further information that we hope will be helpful:

 

There has been a significant increase in our understanding of genetics and genetic testing over the past two decades. Scientists are discovering that many diseases have a genetic component and not just those that are rare.
With over 1,200 disorders and chromosomal abnormalities that can be diagnosed by looking for a specific change in a patient's DNA, medical genetics is more and more recognised as critical in the delivery of patient care. Medical geneticists must therefore have a clear understanding of the different types of diagnostic tests available to patients in order to prescribe the most appropriate test for tier patients.

For approximately 80-90% of hereditary disorders, the genetic cause remains untreatable. This makes sense when we consider the significant increase in our understanding of genetics taking place in a more accelerated pace only in the past two decades along with the significant complexity as well as prohibitive costs involved in accessing genetic testing until recently. As technology has evolved so too have the mechanisms for testing and now there is more than one approach that can yield the results for the empowerment of the patient and the development of greater understanding of disease.  

A Diagnostic Panel covers genes known to be associated with the relevant disease. These genes are sequenced in parallel using Next Generation Sequencing or NGS as it is commonly known. Gene sets in a diagnostic panel are curated selections of genes that are based on the phenotype which refers to the clinical symptoms of the patient.
Each genetic lab has its own panel. It is necessary to choose the panel that suits best each patients particular search.

DNA sequencing is the technique that determines the order of DNA building blocks (nucleotides) in a person’s genetic material. It is one way to test for genetic disorders and it has advanced the study of genetics enormously.
The original sequencing technology was called Sanger sequencing and was named after the scientist who developed it, Frederick Sanger. This was a breakthrough that has helped scientists to determine the human genetic code. However the Sanger sequencing method is relatively time-consuming and expensive. This method is still used in laboratories today but it would take years to sequence all of a person's DNA or genome. 

NGS can be used to sequence all the exons of all genes, the information from that is called ‘Whole Exome Sequencing’ (WES).
With next-generation sequencing all the pieces of an individual's DNA that provide instructions for making proteins can be sequenced. These pieces are called exons, and are thought to make up one percent of a person's genome. Together, all the exons in a genome are known as the exome, and the method of sequencing them is known as whole exome sequencing. With this technology variations in the protein-coding region of any gene can be identified not just a select few. Because most known mutations that cause disease occur in exons, whole exome sequencing is an efficient way to identify possible disease-causing mutations.

Next-generation sequencing technique can also sequence a whole genome, which is called Whole Genome Sequencing (WGS).
Scientist have discovered that DNA variations outside the exons can affect gene activity and protein production and these can lead to genetic disorders. These variations would not be detected by whole exome sequencing. Whole genome sequencing, determines the order of all the nucleotides in an individual's DNA and can determine variations in any part of the genome. This process is fast; a human genome may be sequenced in weeks.
More and more genetic changes can now be identified with whole exome and whole genome sequencing than with select gene sequencing, yet it is important to understand that not all genetic changes affect our health. It is difficult to know whether identified variants are involved in the condition you are concerned with. Sometimes, an identified variant is associated with a different genetic disorder that has not yet been diagnosed and this is referred to as an incidental or secondary finding.
Continued study of exome and genome sequences can help determine whether new genetic variations are associated with health conditions and this can only improve diagnosis in the future.

 

NGS can be used to sequence all the exons of all genes, the information from that is called ‘Whole Exome Sequencing’ (WES).
With next-generation sequencing all the pieces of an individual's DNA that provide instructions for making proteins can be sequenced. These pieces are called exons, and are thought to make up one percent of a person's genome. Together, all the exons in a genome are known as the exome, and the method of sequencing them is known as whole exome sequencing. With this technology variations in the protein-coding region of any gene to be identified not just a select few. Because most known mutations that cause disease occur in exons, whole exome sequencing is an efficient way to identify possible disease-causing mutations.

Next-generation sequencing technique can also sequence a whole genome, which is called Whole Genome Sequencing (WGS).
Scientist have discovered however that DNA variations outside the exons can affect gene activity and protein production and these can lead to genetic disorders. This variations would not be detected by whole exome sequencing. Another method, called whole genome sequencing, determines the order of all the nucleotides in an individual's DNA and can determine variations in any part of the genome. This process is fast; a human genome may be sequenced in weeks.
More and more genetic changes can now be identified with whole exome and whole genome sequencing than with select gene sequencing, yet it is important to understand that not all genetic changes affect our health. It is difficult to know whether identified variants are involved in the condition you are concerned with. Sometimes, an identified variant is associated with a different genetic disorder that has not yet been diagnosed and this is referred to as an incidental or secondary finding.
Continued study of exome and genome sequences can help determine whether new genetic variations are associated with health conditions and this can only improve diagnosis in the future.

The main differences between genetic testing in a clinical setting and research testing is down to the purpose of the test and who receives the results.
Research testing includes finding unknown disease-associated genes, learning the function of the protein product of genes, understanding disease pathways, developing tests for future clinical use, and helping to advance our understanding of genetic conditions. The results of testing done as part of a research study are not always available to patients or their healthcare providers. Clinical testing, on the other hand, is done to identify an inherited disorder in an individual patient or family. People receive the results of a clinical test and can use them to help them make decisions about medical care or reproductive issues.

It is important for people considering genetic testing to know whether the test is available on a clinical or research basis. Clinical and research testing both involve a process of informed consent in which patients learn about the testing procedure, the risks and benefits of the test, and the potential consequences of testing.

Clinical tests are undertaken to provide results to the patient and their medical care provider and so are for the purpose of determinig the diagnosis or treatment of an individual patient.
Clinical test laboratories must be approved to recognised standards. Unlike with research tests, clinical tests will have a charge associated with tem and the cost varies depending upon the test. In the case of clinical tests, the diagnosis is then passed on to the patient.
In general the time between specimen submission and reporting of results varies between laboratories and may be based in part upon the complexity of the testing.

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