Understanding Genetic Testing

Different types of genetic tests are used depending on whether an individual’s chromosomes, the protein-product of a gene, or the DNA itself are examined. Tissues tested include blood, skin, saliva and hair follicles and, prenatally, embryo, placental tissue and amniotic fluid.

For more information about genetic testing and how it is done read our fact sheet

DNA Genetic Testing - screening for genetic conditions and genetic susceptibility

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Prenatal Testing and Screening

Prenatal testing is the process of detecting and diagnosing fetal abnormalities before birth. Many, though not all, fetal abnormalities can now be definitively diagnosed through this process. The tests used to detect fetal abnormalities include ultrasound, CVS (chorionic villus sampling), amniocentesis and blood tests.

More information on prenatal testing

Fact Sheets

Prenatal Testing - Overview

Prenatal Testing – Ultrasound

Prenatal Testing - 1^st and 2^nd trimester screening

Prenatal Testing - CVS & Amniocentesis

Publications

Prenatal Testing: Special tests for your baby during pregnancy
Detailed information about testing available for you during pregnancy.

Prenatal Testing and Counselling
Information about special health tests for your baby during pregnancy, reasons why you might want to consider these tests and related counselling services available in NSW.

Screening Tests for Your Baby in Early Pregnancy
Tests available in the first 12 weeks of pregnancy which can check some aspects of your baby's health.

Publications can be ordered online or by contacting the Centre.

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Preimplantation Genetic Diagnosis (PGD)

PGD involves testing for certain genetic conditions in an embryo created using assisted reproductive technologies (ART) such as in vitro fertilisation (IVF), prior to transferring it to the uterus and allowing it to develop normally. After hormonal stimulation of the woman’s ovaries, some eggs are removed and then fertilised in the laboratory with sperm. One to two cells are removed from the embryo at the eight cell stage (after 3 days) or at blastocyst stage (after 5 days), for testing. Only those embryos that do not have the specific genetic condition that was tested for, will be transplanted into the woman’s uterus. Usually, no more than one or two embryos will be transferred to the uterus at any one time to avoid the possibility of multiple births (more than one baby in a pregnancy). Success rates for having a child from an IVF cycle followed by PGD varies from IVF centre to centre, but tend to follow standard IVF success rates. Like any IVF procedure, stress and often disappointment can accompany PGD. Couples will need to balance the financial and emotional burden of the IVF procedure followed by PGD with that of termination of an affected child conceived naturally.

In Australia, PGD is currently only offered in the private setting.

More information on PGD

Preimplantation Genetic Diagnosis

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Micro Array

As part of an investigation into the developmental or health concern about your child or yourself, your doctor or genetics specialist may suggest a genetic test that looks for extra or missing DNA segments. This test is called a micro array.

A micro array is done by examining the DNA to see if there is more or less DNA than would normally be expected. As there are usually two copies of each chromosome, there should be two copies of each segment of DNA. The test will first look for a variation in the number of copies of the segments (copy number variant). That is, are there more or less than the expected two copies of each DNA segment? When the test finds a copy number variant, the laboratory will check which genes it contains.

Understanding the genes that are present in extra copies or are missing can provide information about:

• The cause of the developmental or health concern

• How symptoms might develop over time

• The possibility of the condition affecting future children.

More information on micro array

Micro Array: Testing for extra or missing segments of DNA

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Paternity and Forensic Testing

The chance that two unrelated people have an identical total DNA gene sequence is at least 1 in 6 million. The closer two people are related to each other, the greater the chance will be that their DNA sequence will be similar. Identical twins have almost exactly the same DNA sequence. The small differences and similarities in the DNA sequence between people are used in genetic testing to determine the identification of individuals.

The tests do not look at the information in the genes but instead examine non-coding DNA that separates the genes along the chromosomes. Specifically, the DNA is examined where there are large numbers of repeated sequences of letters along its length eg. ATTCGATTCGATTCG. As each person has two copies of each chromosome, they will each have two copies of a specific number of repeats of sequences (usually three to five letters in length; called short tandem repeats - STRs).

The pattern of different numbers of STRs at certain sites on the chromosomes are used to create a DNA pattern or DNA fingerprint that is as unique as possible for each person. The number of repeats in each pattern for each person is measured and is used to create a numerical DNA profile for that person. Identification DNA testing using DNA profiling is used as an aid in identifying victims of crime, natural or other disasters such as the terrorist attacks, suspects in a crime and in determining paternity and kinship.

More information on paternity and forensic testing

DNA Genetic Testing – Paternity and Forensic Use

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When parents are relatives - Consanguinity

The term consanguinity describes a relationship between two people who share a common ancestor: a ‘shared blood’ relationship. The most common form of a consanguineous relationship or marriage is between first cousins and in some societies, can account for a large proportion of relationships. Traditionally, some cultures have practised and continue to practise marriage between relatives such as cousins as a means of strengthening family ties and retaining property within the family.

We all carry several harmful faulty gene copies on our chromosomes but have a working copy on the other partner chromosome to provide the information for our bodies. Usually two unrelated people will not carry the same faulty gene copy; therefore, children of unrelated parents are at low risk of inheriting from each of their parents a copy of the same faulty gene that could result in a genetic condition.

People who are blood relatives share a greater proportion of the same genes than unrelated people do because they have a common ancestor such as a grandparent from whom they inherited their genes through their parents. The closer the biological relationship is between relatives, the more likely that they will have the same faulty gene in common. Children of parents who are blood relatives generally have a small increased risk over that of unrelated parents of inheriting from each of their parents a copy of the same faulty gene that could result in a genetic condition.

In most families where the parents are close blood relatives, there will be no history of a specific condition and there are no tests that can usefully be carried out to see if the baby is at risk for being affected by a particular genetic condition. Where there is a family history, or where the parents’ ancestry suggests their risk for having a faulty gene for a condition is increased eg. thalassaemia, genetic testing may be possible to determine if the parents are carriers of the same faulty gene. It is important for couples who are close blood relatives and thinking about becoming parents, to seek Genetic Counselling to obtain current information and explore their reproductive options.

More information on When Parents are Relatives

When Parents are Relatives - Consanguinity genetic testing, screening and prevention.

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Important things to think about

Some ethical issues in human genetics

Ethical issues need to be considered if the benefits are maximised and the harms minimised from the increasing ability to use genetic testing to analyse an individual’s genetic information. Ethical issues that arise are generated from:

• The shared nature and ownership of genetic information. The doctor’s ethical responsibilities include balancing the privacy and confidentiality of the individual and prevention of harm to others (the duty of care). The individual tested also has family responsibilities and obligations including distribution of genetic test results within the family to enable informed decision-making by their at-risk relatives.
• Limitations of genetic testing. While in some cases, genetic tests provide reliable and accurate information on which people can make decisions, in other cases it may not be possible to obtain a definitive result. An individual is much more than the sum of their genes: the individual’s environment can modify the expression of genetic messages to the body and many factors are not genetic that make an individual who they are.
• Inappropriate applications of genetic testing such as for the sole purpose of family balancing (sexing of a fetus for this reason) or its use in paternity testing without the informed consent of all parties involved
• The potential for discrimination especially with the use of information generated by the use of predictive/presymptomatic testing results - generally for adult-onset conditions - in life insurance applications and employment
• Setting boundaries in applications of the genetics technology. This is one of the greatest challenges to find the way to implement regulations internationally such as in the areas of reproductive cloning and genetic testing for enhancement. It is also important to recognise and respect the moral, religious and cultural beliefs that underpin the decision-making by individuals, couples, families or communities
• Forensic DNA databanks. Ensuring that they are used for the purpose for which they were collected and protected from misuse. Also, where the public has also assisted the police by volunteering genetic samples to assist in the investigations of unsolved crimes, ensure that special protections are put in place for the DNA samples and the information generated
• Patenting of genes. Ensuring that commercial interests do not limit equity and access

For more detailed information

Some Ethical Issues in Human Genetics

Life Insurance Products and Genetic Testing in Australia (Fact Sheet 23A)

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How To Access DNA Genetic Testing

DNA genetic testing should always be undertaken by a specialist genetic service. The range and extent of genetics services available will vary throughout Australian States and Territories. Very often the service is based in a specialist paediatric or obstetric department of a hospital. While it is preferable to have a referral from a doctor or specialist in order to access genetic counselling services, an appointment can usually be made without any referral. Health care interpreter services are also available.

Select the area below to view Clinical Genetics Services in that State/Territory:

NSW - Clinical Genetic Services

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Australian Capital Territory - Clinical Genetics Services

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Northern Territory - Clinical Genetics Services

There are currently no clinical genetics services offered in the Northern Territory. Support and information may be available through other specialty services, and from a general medical practitioner.

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Queensland - Clinical Genetics Services

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Victoria - Clinical Genetics Services

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South Australia - Clinical Genetics Services

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Tasmania - Clinical Genetics Services

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Western Australia - Clinical Genetics Services

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New Zealand - General Genetics Services

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