Genetic Testing: Genomic Testing
This fact sheet explains a new form of genetic testing called genomic testing which is used to find
causes of genetic conditions.
What are chromosomes and genes?
Each body cell contains chromosomes,
genetic information. These genetic
determine our appearance and also
development of all organs, such as the
and kidneys and how they work.
which store
instructions
control the
brain, heart
Body cells usually contain 46 chromosomes,
arranged as 23 pairs according to their size. One of
each of these pairs is inherited from our father and
the other from our mother. The first 22 pairs of
chromosomes are similar in men and women. The
rd
23 pair is called the sex chromosomes. These are
called XX in women and XY in men.
The picture shows a cell containing chromosomes.
One chromosome is enlarged and shows that it
consists of DNA from which genes are made.
There are about 20,000 genes in each cell. All of
these genes make up the “genome” in the cell. Just
like the chromosomes, the genes also usually come in pairs, one from each parent. Genes contain
information for the cells of the body to function in the form of code words that the cell “reads”.
Each gene has a specific function, however the function of all genes is not yet known. Variations in the
information can occur which is why we are all unique. Some variations are harmless but others can
make a gene faulty. Variations that make a gene faulty are called mutations and these may be
missing or extra segments of DNA within a gene or a variation in the DNA code.
A mutation in one or more genes may directly cause a genetic condition as the genes do not function
as they usually would in the cell. Some mutations do not directly cause a genetic condition but, in
combination with environmental factors, may increase the chance of a genetic condition developing.
Identifying mutations may help to find the cause of the genetic condition in you or your family which
may be important for you, the affected individuals and other blood relatives. Genetic mutations can be
inherited from one or both parents or may occur for the first time in a person before or during their
conception.
Why is genomic testing done?
Previously, testing to look for mutations involved examining only one gene at a time. It could therefore
take many years to identify the cause of the condition, especially if the condition is one that may be
caused by mutations in one of several genes. It is now possible to test all 20,000 genes at the same
time by genomic analysis. This means that the cause of a genetic condition may be detected within a
shorter time period.
Which genes will be tested?
Firstly, the testing will look at genes that are already known to be involved in directly causing or
increasing risk for the specific genetic condition in you or your family (gene panel testing). If no gene
mutations are found, or if you and your doctor choose to go directly to testing all genes first, then
genomic testing of all the 20,000 genes will occur.
What are the possible outcomes of testing by genomic testing?
1. A gene mutation is found that is the cause of the genetic condition. Your doctor will discuss
these results with you and the meaning of the results for your blood relatives. It is your choice
whether you will inform your relatives to give them the opportunity to participate in genetic
testing, if appropriate. Your family will not be approached by your doctor or genetic counsellor
unless you give permission or it is required by urgent medical circumstances.
2. One or more gene variations are found where the significance is not immediately clear.
Additional testing of other blood relatives may help to determine if the result is relevant in
causing the genetic condition.
3. One or more genetic variations are found but they are known to be harmless and not to cause
genetic conditions. These will not be discussed with you.
4. Rarely, one or more genetic mutations that are not related to the genetic condition being
investigated are found by chance. These are called co-incidental findings. An example of this
could be a gene mutation associated with an increased risk of a serious health problem in you
or your blood relatives. These results will be assessed by an independent committee of
experts in collaboration with your doctor or genetic counsellor. They will discuss these findings
with you if the committee agrees that the results could have important consequences for you
or other family members.
5. No gene mutations are found that could explain the genetic condition. In this situation, more
testing may be available in the future. The timeframe for this is unknown.
The impact of increasing understanding of genetic information on the interpretation of genome
testing
Knowledge of the function of genes and genetic conditions is increasing rapidly and this may mean
that interpretation of results obtained today could change in time. It is possible that you may be
contacted in the future if additional information becomes available regarding the results of genomic
testing but the timeframe in which it could happen are uncertain.
What is required for the genomic analysis?
Your doctor will explain the testing and obtain written consent prior to any testing being done. A blood
sample of 5-20ml (1-2 tubes) will be required from the person being tested from which DNA will be
extracted. In some cases it may also be necessary to test blood samples from other blood realtives
e.g. parents of an affected child to help in understanding the results. You have the right at any time to
withdraw your consent, without affecting the quality of your treatment.
What will happen to the extracted DNA?
When the testing is completed your DNA is stored in the laboratory according to the current NSW /
Australasian guidelines. The DNA may be used for additional testing if it becomes available in the
future.
The use of genomic testing results for research
As well as aiming to provide information for you and your family, the information obtained from
genomic testing is important for increasing knowledge and understanding of genetic mutations and the
causes of diseases. It is therefore important for scientists and doctors to be able to learn about gene
variations that have been identified in your sample. A genome wide analysis of all or most of the genes
in your DNA sample will be performed as part of genomic research to study links to many diseases
and conditions.
In order to allow researchers to share test results, the National Institutes of Health in the United States
(NIH) and other central repositories have developed special data (information) banks that collect the
results of genome studies. The NIH and other data banks will store your de-identified genetic
information and make it available to other qualified researchers to study further. Research using
genome information is important and so the databank will provide study data for researchers working
on any disease. Qualified researchers who can access these databases can be from the government,
academic, commercial or non-commercial organizations. It is unlikely that there will be risks to your
privacy and confidentiality by sharing your genome analysis with these databanks; however, we
cannot predict how genetic information will be used in the future. The information would be deidentified and sent with a code number attached. Any identifiable information would never be given to
the database. There are many safeguards in place to protect your information while it is stored in
repositories and used for research.
There is a very small chance that your genetic information could be shared with others by mistake. In
the unlikely event that your information was mistakenly shared and if it were linked with a medical
condition, this could affect your ability to get or keep some life insurance products. There is also the
risk that data could be released to the public, employers, or law enforcement agencies. If family
members were to see this information it could also affect them and in some instances, this could hurt
family relationships. It is possible that you could be identified from the sample if someone has another
sample from you. The two samples could be matched to identify you from the sample given for this
study.
You will not receive any results from allowing your data to be placed in these databases unless it is
considered medically relevant. No direct benefit can be promised from your participation however the
inclusion of your genome data will contribute to scientific knowledge about genetic problems and
medical conditions.
You can withdraw your consent at anytime if you don not wish your data to be present in these
databases. There will be no consequences for withdrawing consent. However, data that has already
been sent to researchers cannot be retrieved from those researchers.
What if I have any other questions?
If you have any other concerns or questions, please contact your doctor or genetic counselor.