Genetics – frequently asked questions

The most direct way to access genetic services is to speak to your local doctor or GP about a referral.

Your GP will assess your need for genetic services and determine the best service for you to visit depending on your situation. In some cases, your GP may order the genetic test for you, without you having to visit a genetic service.

A geneticist is a doctor who has had specialised training in the field of genetics. They meet with patients to evaluate, diagnose and manage specific genetic conditions.

Usually patients see a geneticist if they have had a genetic test return an atypical result or if they have a condition that appears to have an underlying genetic cause. A geneticist can provide information about genetic testing, the reproductive and health implications of a diagnosis, and the management and treatment of the associated symptoms.

Genetic counsellors works with geneticists to help people understand what having a particular genetic condition means in terms of their health and planning for a family in the future. They are trained to provide information and support that is sensitive to people’s circumstances, culture, beliefs and feelings.

A genetic counsellor aims to equip people with the information they need to be able to make their own decisions, while providing emotional support throughout the process.

A geneticist is likely to ask thorough questions about your own and your family’s medical history. These questions can include aspects of your family’s health such as:

• how you are related to each family member, whether any relatives are adopted into the family, if you have any half- or step- relatives
• any major health conditions that affect family members, and the age of onset of those conditions
• any information available on miscarriages or terminated pregnancies
• the cause of death and age of any deceased family members, if thought to be relevant.

Try to have as much health information on your immediate and extended family as possible. Even facts that you might not think are helpful may still be important.

Write down any questions you have for the geneticists so that you remember to ask about everything you want to know.

Many conditions are inheritable; they can be passed from one generation to the another. Therefore, geneticists like to gather as much information as possible on your family medical history.

This information helps geneticists work out whether the condition may be genetic and, potentially, make a diagnosis.

Genetic conditions can only be definitively diagnosed with a genetic test.

Some genetic conditions have distinctive physical characteristics that clinicians can identify. This can help them to propose a diagnosis, for which they would then arrange genetic testing.

Currently genetic conditions do not have a cure. However, many conditions can be effectively managed by the use of:

• medications
• physical therapies
• teaching aids in schools.

Families and individuals may also find it beneficial to be put in contact with support network groups and other families who are living with the same condition.

Genetic testing examines an individual’s DNA for changes that could cause a condition. The results of a genetic test can confirm or rule out a suspected genetic condition.

Results from genetic tests can also provide families with insight about the risks of future family members inheriting the condition and if another member in the family is likely to develop symptoms.

There are different methods used for genetic testing:

• Molecular genetic tests can examine and study individual genes or small amounts of DNA for changes that could cause a genetic condition.
• Chromosomal genetic tests, including microarrays, are used to analyse whole chromosomes to see if there are large genetic changes that affect more than one gene. These tests can be used to diagnose conditions like Down syndrome, which is caused by a person having an extra copy of chromosome 21.
• Biochemical genetic tests can be used to measure the amount or activity levels of different proteins. Irregular results for certain proteins can indicate a genetic condition caused by a change in DNA.

Genetic testing requires a sample of the person’s DNA. Depending on the test type, doctors can ask for DNA from different sources. The most common samples used in genetic tests are saliva and blood, but hair and skin can also be used. All of these sample types are relatively easy to take. Some more specific prenatal tests can require a sample of amniotic fluid (the fluid that surrounds the fetus in the womb).

The DNA sample is then sent to a laboratory where it is tested for specific changes, depending on the condition the doctor thinks the person may have.

 

Non-invasive prenatal testing, or NIPT, is a test offered to pregnant women to assess the chance that the fetus will be born with certain genetic conditions. It is a screening test and can provide parents with an estimated chance of a condition. If parents want a definitive diagnosis, further testing is needed.

NIPT analyses small genetic fragments in the mother’s blood. Some of these fragments come from the placenta and contains the fetus’ DNA. This provides the opportunity for the early detection of a condition. NIPT poses limited risk to the fetus because the DNA sample is taken from the mother’s blood.

NIPT is commonly used to assess the chance of a fetus having a chromosomal condition that is caused by an extra or missing copy of a chromosome. NIPT looks for common trisomy conditions such as Down syndrome (trisomy 21), Patau syndrome (trisomy 13) and Edwards syndrome (trisomy 18), and missing or extra copies of the X and Y chromosomes.

NIPT may also be used to screen for other chromosomal conditions caused by the addition or deletion of sections of a chromosome. 

Newborn blood screening is a simple blood test taken from the heel of a child within three days after birth. It tests for three rare but serious medical conditions: phenylketonuria (PKU), hypothyroidism and cystic fibrosis. These conditions are life threatening if not treated but show minimal to no physical symptoms at birth. This blood test identifies these conditions early on and allows effective treatments to be implemented before symptoms progress.

Genetic testing for the purpose of a medical diagnosis is done through certified healthcare professionals. It is often requested by a doctor and completed in a certified clinical laboratory.

Genetic tests that can be ordered online (direct-to-consumer tests) are different. Those genetic tests are marketed directly to customers. They offer tests for a variety of purposes, ranging from health condition risks to ancestral information. There is currently very little regulation of direct-to-consumer testing, so it is important to assess the quality and validity of services before having any sort of testing. 

The out-of-pocket costs for genetic tests done in Victoria depend on the test and whether other family members have a genetic condition. 

If someone is diagnosed with a condition that is inheritable, at-risk family members may be eligible for testing that is subsidised by government funding. This is known as cascade testing. 

For more information about the cost of specific genetic tests, contact VCGS or your local health care professional. 

Your genome contains your complete set of genetic information (or genes). Whole genome sequencing (WGS) is a test used to determine the complete sequence (or code) of your DNA.

Your exome is the part of your DNA that codes for proteins. It makes up one to two per cent of your total genome. Whole exome sequencing (WES) is a tool used to examine your exome. It aims to identify changes in your exome that may help diagnose your medical condition and, in turn, help with its treatment. 

WES is a quicker test than WGS, as the amount of DNA that needs to be analysed is much smaller.

DNA stands for deoxyribonucleic acid. It is what your chromosomes are made of, and it is passed down through families. DNA is found in every cell of your body. Most DNA is located within the nucleus of the cell, but some is also found in the mitochondria (the cell’s ‘powerhouse’).

DNA is composed of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T). The order that these four bases are placed in determines the genetic code of that individual. This code provides all the instructions for development, survival and reproduction.

Genes are the blueprint for your body. They are made of DNA and you have around 20,000 to 25,000  of them in almost every cell in your body. Most genes come in two copies, one inherited from your mother, the other from your father. Some genes provide instructions for your body to make proteins. Proteins are molecules that provide the structure for your organs and tissues and enable them to function. They do most of the work in your cells.

A condition is inherited when it is passed down from parents to their children. Children inherit two copies of each chromosome, one copy from each parent. If a parent is carrying a changed copy of a gene on one chromosome, there is a fifty per cent chance of a child inheriting that changed copy. 

A genetic trait is a physical characteristic, such as eye or hair colour, or a genetic condition. When a trait is inherited in a dominant manner it means that one copy of the changed gene is enough to cause the condition or characteristic. If a parent has a dominant condition, then each of their children will have a fifty percent chance of inheriting that condition.  

A recessive trait is one that is only expressed when there are two copies of the changed gene present. So, to show symptoms of a recessive trait, an individual must have inherited two copies of the changed gene. Because of this, recessive traits can be ‘hidden’ in families. 

If a person inherits one changed and one unchanged copy of a gene for a recessive trait, they will not show any symptoms, but they will have a fifty per cent chance of passing that changed gene on to their children. 

An X-linked trait is a condition that is caused by a gene change on the X chromosome. X-linked conditions can be dominant or recessive. They are more commonly observed in males than females. 

Females typically have two copies of the X chromosome. Therefore, if they inherit one changed gene copy on one X chromosome, they have another regular copy on the other X chromosome to compensate for it.

Males typically only have one X chromosome, so if they inherit a changed copy, they only have that changed copy.