FAQs – Mackenzie’s Mission
What does it mean to be a ‘carrier’ of a genetic condition?
Every person has two copies of most genes – one from each parent.
A person is a ‘carrier’ when they have one copy of a faulty gene (a gene mutation) associated with a genetic condition, but their other copy of the gene is functioning normally. They won’t have the genetic condition themselves, but will be a ‘carrier’ of the condition.
A carrier can pass on this faulty gene or genes to their children. When a faulty gene associated with a genetic condition is passed on to a child by each parent – this means the child has two faulty genes and no healthy copy – the child will have the genetic condition.
It is estimated that all people are carriers of several recessive genetic conditions, without ever realising it. When two people who carry a fault in a gene for the same condition have children, for each pregnancy, there is a 1 in 4 (25%) chance that their child will inherit faulty copies of the gene from both parents, and have the genetic condition.
Image shared with permission of the Genetic Support Foundation.
Mackenzie’s mission will also screen for X-linked conditions.
Women have two X chromosomes and men have one X and one Y. If there is a faulty gene on the X chromosome it can cause a genetic condition. Usually boys and men are more severely affected by X-linked conditions than girls and women – women may be healthy carriers who do not show any signs of the condition.
Image shared with permission of the Genetic Support Foundation
So, what is carrier screening?
Carrier screening is a form of genetic testing used to see if a person is a carrier of recessive or X-linked genetic conditions that could be passed on to their children.
What is reproductive carrier screening?
When couples who are planning a family or are in the early stages of pregnancy have carrier screening, it is known as reproductive carrier screening. This means the test looks at the genetic information of both the mother and father together to see if, as a couple, they have an increased chance of having a child with a genetic condition.
Why is reproductive carrier screening important?
Recessive and X-linked genetic conditions are a major cause of death and chronic illness in children. It is estimated that more than one million people in Australia are affected directly or indirectly by a genetic condition. Carrier screening for those planning a family, or in early pregnancy, enables couples to make informed choices according to their own personal wishes and values.
Who should be offered reproductive carrier screening?
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists have recently published the following recommendation to provide guidance on who should be offered reproductive carrier screening:
“Information on carrier screening for the more common genetic conditions that affect children (e.g. cystic fibrosis, spinal muscular atrophy, fragile X syndrome) should be offered to all women planning a pregnancy or in the first trimester of pregnancy. Women wanting more information about carrier screening should be given the opportunity to have a more detailed discussion about carrier screening with an informed clinician. The benefits and limitations of testing, and any associated costs should be discussed.”
Do other countries have reproductive carrier screening programs?
Yes. Many countries have carrier screening in place for recessive conditions. In Australia, carrier screening for thalassaemia, a genetic blood disorder, is government funded and screening for other conditions including cystic fibrosis, spinal muscular atrophy and fragile X syndrome is available on a user-pays basis. Many countries have carrier screening programs for variable numbers of conditions with some being government funded and some being user-pays.
What conditions does this study screen for?
The project will screen for autosomal recessive and X-linked genetic conditions affecting children where those conditions are severe and life-limiting, and for those where early treatment can improve a child’s health.
It will include spinal muscular atrophy (SMA), fragile X syndrome (FXS), cystic fibrosis (CF) and around 500 other genes associated with severe, life-limiting conditions.
Why does the project screen for changes in around 500 other genes?
About 500 genes are being selected because this number is technically achievable and will make it possible to detect the great majority of couples who have an increased chance of having children with the recessive and X-linked conditions that affect Australian children.
Do couples have to participate in this study?
No, this is a research study and participation is optional. Couples will be provided with information and support to help them make an informed choice about whether or not to participate.
What do we mean by a pilot study?
Before reproductive carrier screening can be made widely available, a large pilot study needs to be done to answer some important questions like: How do couples feel about having carrier screening? What choices do couples make before and after having screening? What information do we need to provide health professionals to deliver screening? What resources does our health system need to ensure screening can be accessed by those who wish to have it? What infrastructure is needed for screening to be delivered at scale in the Australian population?
How many couples will participate?
Ten thousand couples will be screened as part of the study. We aim to enrol a broad sample of couples that reflects the diversity of the Australian population. This is important to ensure the outcomes of our research are applicable to the population as a whole.
What options are there for couples found to have a high chance of having a child with one of the conditions for which they are screened?
If a woman is pregnant at the time the couple is found to have a 1 in 4 chance of having a child with one of the conditions, there is the option of having testing of the pregnancy by chorionic villus sampling or amniocentesis (prenatal diagnosis). If the pregnancy is affected, termination of the pregnancy may be considered.
If not pregnant when identified to have a 1 in 4 chance of having a child with a genetic condition, then in addition to the option of prenatal diagnosis, couples could choose to have testing of embryos produced by IVF (preimplantation genetic diagnosis, PGD), use donor egg, sperm or embryo, adopt children or choose not to have children. One cycle of PGD will be available free of charge to all eligible couples identified through Mackenzie’s Mission.
For some conditions, early diagnosis can lead to more effective treatments. In addition to the options above, couples who are found to have an increased chance of having a child affected by such a condition may choose to test the child at birth.
How do couples participate in this study?
Couples can enrol in the study only through health professionals involved in the study. General practitioners, obstetricians, midwives, geneticists and genetic counsellors at specific sites around Australia will recruit couples for the study.
Couples planning a family, or who are in early pregnancy, will be asked by their participating health professional whether they wish to be involved in the study. The health professional will then provide the couple with further information about reproductive carrier screening and the risks, benefits and possible outcomes of their involvement in the study, and details on how to enrol. A telephone helpline will be available for couples considering enrolling in the study to talk to a genetic counsellor, should they have further questions.
When can couples participate in the study?
The project will start in Victoria, Western Australia and New South Wales. It is expected that couples in these states will be able to participate in the study from late 2019. The study will then open in all other states and territories through participating health professionals in late 2020. It is scheduled to finish at the end of 2021.
For more information about autosomal recessive and X-linked inheritance see:
Fact Sheet on Autosomal Recessive inheritance
Fact Sheet on X-linked Recessive inheritance
Mackenzie’s Mission is the first project to be funded from the $500 million Australian Genomics Health Futures Mission - part of the Australian Government’s Medical Research Future Fund.
For all enquiries relating to Mackenzie's Mission, please contact firstname.lastname@example.org